MOTORCYCLE OPERATION and SERVICE Jay Webster and Robert Putnam Digitized by the Internet Archive in 2010 http://www.archive.org/details/motorcycleoperatOOwebs MOTORCYCLE OPERATION AND SERVICE MOTORCYCLE OPERATION AND SERVICE Jay Webster California State University Long Beach Robert Putnam R A RESTON BOOK Prentice-Hall Englewood Cliffs, New Jersey 07632 Library of Congress Cataloging in Publicaiion Data Webster, Jay. Motorcycle operation and service. "A Reston book." — 2. Motorcycles Maintenance and Putnam, Robert E. II. Title. TL440.W38 1986 629.2'275 85-19591 ISBN 0-8359-4669-X 1. Motorcycles. repair. © I. 1986 by Prentice-Hall Englewood A Cliffs, N.J. 07632 Reston Book Published by Prentice-Hall A Division of Englewood Simon & Cliffs, N.J. Schuster. Inc. 07632 No part of this book may be reproduced in any way or by any means without permission in writing from the publisher. All rights reserved. 10 98765432 1 Printed in the United States of America '.^ 7 PREFACE UNIT 1 1 ix 1 Motorcycle Basics Types of Motorcycles Components Basic Motorcycle UNIT 2 Safety In the Motorcycle Job Competency Objectives Personal Safety CONTENTS 1 1 2 Shop 5 5 Hand Tool Safety 7 Power Tool Safety 10 Compressed Air and Parts Cleaning Fires and Fire Prevention Gasoline and Liquid Flammables Battery Safety 1 1 12 13 Shop 14 Discussion Topics and Activities 15 Riding a Motorcycle in the Key Terms 14 Checkup 14 UNIT 5 Assembling and Fastening Devices Job Competency Objectives UNIT 3 Tools Fasteners with Threads 17 Job Competency Objectives Screwdrivers Wrenches Pliers Thread Repair 17 Key Terms 1 Checkup 19 Hammers 47 52 58 59 Discussion Topics and Activities 24 47 47 59 26 Service Manuals 27 Key Terms 28 Checkup 30 UNIT 6 Engine Fundamentals Job Competency Objectives 61 61 Basic Engine Parts and Operation UNIT 4 Measuring 61 Two-Stroke Cycle Engine Operation Four-Stroke Cycle Engine Operation 63 66 Engine Size and Performance Measurements Key Terms 72 Checkup 72 31 Job Competency Objectives Metric Measuring System Metric Units of Measure 31 31 31 English (Customary) Measuring System 32 Discussion Topics and Activities 69 73 Converting Between Metric and English Measurements 32 Using Measuring Tools UNIT 7 Upper-End Parts and Construction 34 Key Terms 44 Checkup 44 Discussion Topics and Activities Job Competency Objectives 45 Cylinders 75 75 75 1 vl 1 CONTENTS 79 Piston Rings Piston Pin 81 Cylinder Head Valves Lower-End Troubleshooting Lower- End Servicing 160 Key Terms 176 Checkup 76 75 Pistons 81 59 1 82 176 Discussion Topics and Activities Valve Guide Valve Seat 1 83 83 84 Valve Springs, Retainers, and Seals Camshaft UNIT 12 Lubrication System Operation and Servicing 177 85 Key Terms 85 Checkup 86 Job Competency Objectives Discussion Topics and Activities 87 UNITS Friction and Lubrication 177 177 Four-Stroke Lubricating Oil 178 Two-Stroke Lubricating Oil 178 Four-Stroke Lubrication Systems 178 Two-Stroke Upper-End Troubleshooting and Servicing 89 Two-Stroke Lubrication Systems 182 Job Competency Objectives Troubleshooting Top-End Troubleshooting Top-End Servicing 93 Key Terms 110 Checkup 1 10 89 186 187 Key Terms 192 Checkup 192 89 Discussion Topics and Activities Discussion Topics and Activities 1 192 10 UNIT 13 Cooling System Operation and Servicing 193 UNIT 9 Four-Stroke Upper-End Troubleshooting and Servicing 111 Job Competency Objectives Top-End Troubleshooting 1 Top-End Servicing 115 Key Terms 148 Checkup 148 UNIT 10 Engine Lower End Discussion Topics and Activities 149 Job Competency Objectives 149 205 207 Four-Stroke Exhaust Systems Two-Stroke Exhaust Systems Turbocharging 207 207 210 Key Terms 214 Checkup 214 155 155 Discussion Topics and Activities Discussion Topics and Activities 159 UNIT 15 Fuel System Operation 217 Job Competency Objectives 217 Carburetor Fundamentals A 159 215 158 UNIT 11 Lower-End Troubleshooting and Job Competency Objectives 198 148 Key Terms 156 Checkup 157 Servicing 193 Key Terms 204 Checkup 204 149 Connecting Rods 193 193 Cooling System Troubleshooting and Servicing 149 Chrankshaft Air Cooling Systems UNIT 14 Exhaust Systems and Turbocharging Job Competency Objectives Chrankcase Job Competency Objectives Liquid Cooling Systems 1 1 1 Discussion Topics and Activities Bearings Lubrication System Servicing Basic Carburetor 217 218 Carburetor Metering Systems 219 207 CONTENTS 224 Constant- Velocity Carburetors Carburetor Size Wiring Diagrams 225 292 Using Basic Test Instruments 226 Air Intake vii 293 Key Terms 296 Checkup 296 Key Terms 226 Checkup 229 Discussion Topics and Activities Discussion Topics and Activities 296 231 UNIT 20 UNIT 16 Battery and Charging Servicing 297 System Operation and Fuel System Troubleshooting and Servicing 233 Job Competency Objectives Job Competency Objectives Battery Construction and Operation 233 Fuel System Troubleshooting Fuel System Servicing Charging System Operation 233 The Alternator 302 The Rectifier 303 The Voltage Regulator 236 Key Terms 248 Checkup 248 248 Discussion Topics and Activities 297 297 301 303 Charging System Servicing 308 Key Terms 313 Checkup 313 UNIT 17 Discussion Topics and Activities System Operation Ignition Job Competency Objectives 249 Ignition 252 Systems Capacitor Discharge Systems Ignition Timing Spark Plugs UNIT 21 Starting and Accessory Systems Job Competency Objectives 315 The Starting System 315 Accessory Systems 320 Key Terms 324 Checkup 324 249 Battery Coil Ignition Systems Magneto 254 256 256 Key Terms 261 Checkup 262 Discussion Topics and Activities 264 UNIT 18 Ignition 313 249 Discussion Topics and Activities 315 325 UNIT 22 System Troubleshooting and Servicing 265 Job Competency Objectives Job Competency Objectives 265 Primary Drive Troubleshooting the Ignition System Primary Drive and Clutch Operation and Servicing 327 265 Clutch System Servicing Key Terms 284 Checkup 284 Ignition 327 330 330 Primary Drive Troubleshooting and 268 Servicing 333 Clutch Troubleshooting and Servicing Discussion Topics and Activities 284 Discussion Topics and Activities UNIT 19 Fundamentals of Electronics 285 Electricity Job Competency Objectives Electricity Electronics 290 287 346 and UNIT 23 Transmission and Final Drives Job Competency Objectives 285 Electrical Terms Magnetism 289 285 335 Key Terms 343 Checkup 344 Transmission Final Drives Key Terms 347 353 366 347 347 vlll CONTENTS Checkup 366 Brake Servicing 404 Key Terms 367 Discussion Topics and Activities Checkup 418 418 Discussion Topics and Activities UNIT 24 Frame and Suspension Job Competency Objectives Frame 369 UNIT 26 and Wheel Operation and Servicing 369 Tire 369 Suspension Job Competency Objectives 374 Key Terms 391 Checkup 391 Tires Discussion Topics and Activities Job Competency Objectives Drum Brakes Hydraulic Disc Brakes 421 Discussion Topics and Activities 395 395 395 399 421 Wheel Assembly 425 Wheel Hub Assembly 430 Key Terms 439 Checkup 439 394 UNIT 25 Brake System Operation and Servicing Mechanical 420 INDEX 441 440 421 — Motorcycle Operation and Ser\'ice training needs of purpose of the text is designed to meet the student motorcycle technician. tiie The motorcycle instructor to help the is present basic principles that are valuable in the instruction of students various levels of training. at The text can be used to train entry-level motorcycle technicians and to re- and upgrade train skills of practicing motorcycle techni- cians. Motorcycle Operation and Service provides students with a foundation in the basics of motorcycle mechanics with special emphasis in hands-on training. The principles PREFACE of operation of motorcycle components are followed by the principles of maintenance, troubleshooting, and service. A motorcycle technician with a thorough understanding of operational concepts and service techniques will be better prepared to service the high technology motorcycles of the future. The book is organized into 26 units. Units provide the student with basic work successfully 1 through 5 information required to in the shop. Units are devoted to motor- cycle basics; safety; tools; measuring; and assembling and 10 focus on the two- fastening devices. Units 6 through and four-stroke motorcycle engine. The fundamentals of engine operation are presented first, followed by upper-end and construction. As soon as the student understands parts the parts and operation, units are presented on trouble- shooting and service. There are troubleshooting and servic- The enfollowed by a unit Each unit has a set of "Key Terms" ing units for both four- and two-stroke upper end. dents' learning. gine lower end is presented in a on lower-end troubleshooting and signed to help in the job of vocabulary development. Each The engine units are followed unit, "Checkup" unit ends with a set of service. by engine accessory units. Units 12 through 21 present the operation, troubleshooting, de- questions to help the student and the instructor determine if the student under- stood the content of the unit. A set in each unit for the student of "Discussion Topics and servicing of the accessory systems necessary for en- and Activities" gine operation. There are units on the lubrication system; who cooling system; exhaust system and turbocharging; fuel on a topic. Job Sheets have been developed for each troubleshooting and servicing unit. The purpose of the job sheets is to system; ignition system; battery and charging systems; and and accessory systems. starting When is the study of the engine and its accessory systems complete, the transmission of power from the engine to wheel the rear is presented. The transmission of power is presented in Units 22 and 23. First the primary drive and clutch operation and service transmission and final drive. and 26 are devoted There and A a unit is tires to presented, followed by the The last three units, 24, 25, the motorcycle chassis systems. on frames and suspension; brake systems; and wheels. special effort has eration is and Sen'ice an been made to make Motorcycle Opeffective learning tool. Illustrations developed from the simple to the complex follow- is provided ahead of the rest of the class or who is interested in further study help the instructor guide the student through the shopwork activities. Each job sheet specifies what reading the student should do before the job and provides blanks to garding the motorcycle and the time Each job sheet lists it ations. in re- the special tools, equipment, parts, and for the student to write in turer's fill do the job. takes to materials necessary to complete the job. There shop manual. the student provide direct visual correlation to the text material. Topics are is A any reference to a specification section is is provided so must look up and record any necessary The procedure a space manufacspecific- section gives the basic steps for the completion of the job. There are checkpoints for the structor to student to in- check the students' progress and blanks for the fill in the results of tests or measurements. Each begins with "Job Competency Objectives." These unit are Jay Webster measureable objectives designed to guide the stu- Robert Putnam ing techniques that have been tested in the shop. specific IX MOTORCYCLE OPERATION AND SERVICE word motorcycle is a combination of the words moThe first motorcycles were just that bicycles on which a backyard mechanic installed a small motor. The motorcycle has come a long way since those days, having evolved into a complex machine with many sysI he — tor and bicycle. tems and thousands of parts. Today's motorcycles are extremely powerful, more able, and easier ago. New to control than those of technology in motorcycle engine development, suspension design, and electronics has resulted els reli- even a few years in new lev- of performance and reliability. The only negative effect of these developments complex than cian must it was is that the motorcycle in earlier times. now have a A is much more motorcycle techni- good understanding of basic motor- cycle systems and a good deal of experience servicing those systems. The purpose of this book is to help the be- ginning motorcycle technician understand the basic operating principles and servicing techniques of the motorcycle. TYPES OF MOTORCYCLES Over the years the number and types of motorcycles on and off the roads have increased. Today, there is a type of motorcycle for just about everyone. The moped has become an increasing popular and fuelway to get around. The term moped is a combined form of motor and pedal. The moped (Figure 1-1) is a cross between a motorcycle and a bicycle, combining some efficient of the better features of each. Like a bicycle, able, easy to operate, highly maneuverable, transportable by car. Like a motorcycle, it is it pedal- is and handily motor driven, features handlebar acceleration, offers headlights, and turn signals, and demands the operator. Mopeds low center of gravity little effort on the horns part of often have a no-shift transmission; a for easier, safer balance; and a handy step-through design for easy mounting. They usually have a very small engine that is able to squeeze about 150 miles out of a gallon of gasoline. However, the rider often has to help the machine by pedaling on the steeper grades. UNIT 1 : Motorcycle Basics Figure 1-5. Today's street bikes have hightechnology engines and are extremely aerodynamic. (Kawasaki Motors Corp.) Figure 1-3. The three-wheel machine is a (Kawasaki Motors development. recent Corp. U.S.A.) Figure 1-4. The four-wheel all-terrain machine IS a variation of three-wheel bikes. (U.S. Suzuki Motor Corp.) reduction as through the possible air. The in the drag created Figure 1-6. any number A of motorcycle can be fitted with accessories for touring. (Har- ley-Davidson Motors, Inc.) by pushing level of technology of these machines increases with each yearly model. Street machines can be equipped with any number of ac- cessories for comfort and touring (Figure 1-6). To many people, the joy of motorcychng resides in comfortable, long-distance travel. Some quently, and riders like both off-road many street riding. Conse- bikes are manufactured with off- road sus- pensions but are equipped with lights and other accessories for street riding (Figure 1-7). BASIC MOTORCYCLE COMPONENTS All types of motorcycle have the and systems. When you Figure 1-7. This bike has maximum suspension travel for off-road riding but lights and exhaust for street operation. (Kawasaki Motors Corp. U.S.A.) same basic components understand the basic operating principles behind these systems, you will be able to diag- nose problems and make repairs on them. niting Engine ful The motorcycle engine (Figure 1-8) verts heat energy to a and burning of an air-fuel mixture to produce heat. air caused by the heat produces use- The expansion of the is a machine that con- form of power. All motorcycle en- gines operate on the principle of combustion, i.e., the ig- power. There gines. and are, of course, We their many shall consider both many types and designs of en- two- and four-stroke engines design variations. BASIC MOTORCYCLE COMPONENTS Figure 1-8. The engine supplies the power. (Kawasaki Motors Corp. U.S.A.) Figure 1-10. The fuel system provides air. (Kawasaki Motors Corp. U.S.A.) fuel and Figure 1-9. Exhaust system. (Kawasaki Motors Corp. U.S.A.) Figure 1-11. The tems. A gine's moving parts in order to prevent the metal-to-metal moving lows the parts to move more easily because between them. The lower the engine, the more power An system. (Kawa- lubrication system circulates oil between the en- contact which causes wear. Oil between friction ignition saki Motors Corp. U.S.A.) In order to function, an engine requires a set of subsys- it it parts al- lessens the internal friction of an can develop. exhaust system (Figure 1-9) provides a smooth flow maintaining of exhaust, maximum engine performance while minimizing the noise. A fuel system for several to the engine, amounts for An (Figure 1-10) is used to store enough hundred miles of operation, and mix to efficient fuel to deliver the fuel the fuel with air in the proper burning inside the engine. ignition system (Figure 1-11) is used to provide a high-voltage spark in each of the engine's cylinders so that the air-fuel mixture will explode. The Figure 1-12. The ignition system dis- electrical system. (Kawa- saki Motors Corp. U.S.A.) tributes the high voltage to each of the cylinders at just the right time for a power stroke. The electrical system has several subsystems. The charging system restores the chemical energy used by the Electrical system The system of a motorcycle (Figure 1-12) pow- battery. electrical ers all the electrical components of the machine. It consists of a battery that provides a source of stored energy that operates the electrical the engine is components of the motorcycle when not running. It develops all the power required to the motorcycle's electrical system once the engine ning. The operate is run- electric starting system allows the rider to use the energy stored in the battery to power a starter motor to crank the engine. Electrical accessory systems include headlights, turn signals, brake lights, and horns. 4 UNIT 1 Motorcycle Basics : Figure 1-13. Drive train. (Kawasaki Motors Corp. U.S.A.) Figure 1-15. The brake system. (Kawasaki Motors Corp. U.S.A.) Figure 1-14. Frame and suspension. (Kawasaki Motors Corp. U.S.A.) Figure 1-16. Tires and wheels. (Kawasaki Motors Corp. U.S.A.) TIRES AND WHEELS Brake system Drive train The purpose of After the engine develops to the rear its power, the power is delivered wheel of the motorcycle by an assembly of called the drive train (Figure 1-13). parts The components of the motorcycle brake system (Figure 1-15) down the rotation of the wheels to allow rider to slow down or stop the bike. Motorcycles may a mechanical drum brake or a hydraulic disc brake. is slow to the use the drive train are a set of primary gears: the clutch, used to connect and disconnect the engine's power from the Tires and wheels drive train; the transmission, which provides the rider with a selection of different gear ratios to match engine power output with motorcycle speed; and a final drive that delivers the power to the rear wheel through a chain-and- sprocket or shaft assembly. The tire-and- wheel move down The motorcycle frame provides which the engine and drive the basic foundation onto train, as well as all the other components, are mounted. The frame works with the susride. it and wheel provide directional control, while the rear tire and wheel deliver the road. power to the road to push the motorcycle for- ward. pension system (Figure 1-14) to provide the rider with a smooth The front tire to the engine's Frame and suspension assembly of the motorcycle (Figure 1-16) supports the weight of the motorcycle and allows Each of the major motorcycle components is important and safe riding of the motorcycle. Accordingly, our study of motorcycles begins with units on safety and the use of tools and fasteners. From there, we proceed to a consideration of each of the above systems in detail. to the operation In working on motorcycles, you number will be using a of tools and materials that can be hazardous if they are not handled properly. In various areas of work every year, more than two million people are injured and about 13,000 are killed because of occupational hazards. To many are not just numbers, however, to the people of those statistics peo- might seem to be just numbers. They ple, these statistics — who are part people who, for example, have lost an eye or a limb due to an on-the-job accident. Since safe work habits prevent accidents, it is important that you follow good work habits and be familiar with common safety practices in the shop. Remember: Safety is everybody's business! It's your life. JOB COMPETENCY OBJECTIVES When you be able finish reading and studying you should this unit SAFETY IN THE MOTORCYCLE SHOP to: 1. Demonstrate your knowledge of personal safety by working safely in the shop. 2. Demonstrate the safe use of common hand tools. Recognize the possible hazards when using power 3. tools. Demonstrate the safe use of compressed 4. and parts- air cleaning equipment. Recognize the hazards 5. in handling batteries. Describe the safe handling of gasoline and 6. tinguish a gasoline Explain 7. how how to ex- fire. to ride a motorcycle safely in the shop. PERSONAL SAFETY Safety begins with you! Your personal appearance and be- havior can prevent accidents from happening to yourself or to those around you (Figure 2-1). You must learn to prac- way you look, when you perform motorcycle repair work. tice personal safety in the Personal appearance it and act an important part of personal you wear your hair long, you should be aware safety. If that is dress, only takes an instant for it Figure 2-1. Safety is everybody's business. Motor Corp.) to get entangled in rotat- (U.S. Suzuki ing machinery and yanked out by the roots. If you do have long hair, it should be either tied back or contained by a cap or bandana to prevent it from falling into your eyes and work. What you wear is close-fitting clothing also important to your safety. and keep it zipped up. Loose clothing, such as shirt tails, ties, lapels, cuffs, or scarves can easily get caught or machinery and cause serious bodily injury. few moments to keep neat. Take the time. Wearing jewelry can also be dangerous. wear any at Wear tucked in and buttoned or work. Jewelry can catch wrapped up It in only takes a And remember that metal jewgood conductor of electricity. Always wear eye protection when you are doing any kind of job that may endanger your eyes. Always wear eye protection while using a grinder of any kind. Even if the bench tool grinder has its safety guard in position, wear just as loose clothing can. elry is also a eye protection. Wear eye protection when working around caustic fluids, such as battery acid or cleaning fluid. Your shop will have protective glasses or face shields (Figure It is in rotating best not to machinery. 2-2). It is a good idea to wear the eye protection time you are in the shop. all the UNIT 6 2: Safety In the Motorcycle Shop Figure 2-2. Eye protection should be used when working Safety glasses or a safety shield is worn. (Florin Limited) Foot protection is also a must. Heavy in hazardous areas. tools and motorcy- can easily be brushed off the work bench. Safety cle parts shoes with steel-capped toes can save a great deal of pain or even broken toes. Always wear safety shoes in the shop. Gloves may be needed for inserting parts into a cold tank and then removing them, and for handling storage batteries. Proper behavior can also help prevent accidents. Horseplay is not fun when it sends someone to the hospital. Such things as air nozzle fights or practical jokes do not have any place in the motorcycle shop. Remember, you are at work, and both work and safety are serious business. To prevent injury to yourself or to your fellow workers, never use power machinery or attempt a repair job until you have received proper instructions from the appropriate authority. If you are in doubt, or if you are unfamiliar with a power tool or a repair process, ask for help. Never risk going ahead You until you are sure. should also always pay attention to specific and carrying rules. Lift with Figure 2-3 shows the recommended You may lifting your legs, not with your back! lifting techniques. be as strong as an ox, but be careful when you Even if your back muscles were made of steel, there would be a limit to the strain they could stand. Size up the load before you try to lift it, and get help if necessary. If lift. Figure 2-4. Keep your work area clean and Motor Corp.) well organized. (U.S. Suzuki you must lift Lift straight the load alone, use your legs, not your back. up by straightening your not to twist at your waist when legs. Also, take care lifting. Twisting while lift- ing can cause a severe injury to your back. Personal housekeeping is very important. Always keep your personal work area clean and well organized (Figure Figure 2-3. Lift heavy objects with your legs, not your back, (Ford Motor Co.) 1-^). Have a place for each tool, and keep not in use. Clean up all oil spills it there when immediately, especially . HAND TOOL SAFETY those on the floor. Do not allow machine parts, fasteners, or other dehns to clutter up your work surface or to accu- mulate on the floor. Do not keep any oily cleaning rags around your work area because they are a pose of oil> rags in a tire hazard. Dis- CORRECT; covered metal contamer provided for that purpose. Be aware of your surroundings. Locate your work in relation to key emergency points. est first-aid kit is located. If your instructor. Usually, a it is list cluded inside the cover of the Know where and even. tell kit's contents is in- kit. Facilities Find out where the nearest fire WRONG: for flushing the exdnguisher is Make extinguisher, i fire wrill mar fire you know how to use the fire extinguisher, and make sure you use the correct class of fire sure Classes of Oversize screwdriver tip work and may damage the screw head. located! prominent red sign should mark the location of each extinguisher. ^ area eyes should also be in or near the shop area. .A must fit the bead must be flat the near- not properly stocked, of the Screvddriver tip of the screw. Tip of screwdriver WRONG: Rounded tip will damage the screw head. extinguishers will be covered WRONG later.) Find out where the nearest telephone sure that the telephone pital, the fire number of is located. .Make Figure 2-6. Use a correct-size screwdriver ,oc {Stanley Works) a doctor, the nearest hos- for -.ne department, the police department, and any other numbers you might call in an emergency are posted next to the telephone. to If the numbers are not posted, talk your instructor. HAND TOOL SAFETY all your hand tools for cracks, chips, burrs, broken teeth. and other dangerous conditions before you use them. If any defective tools are found, take them to your instructor so that no one can be injured using them. The basic rule is; Use the tool to do the job it is designed for. good motorcycle technician has a place where every for tool use Hand sound, clean, workable A condition. Greasy hand tools can easily slip out of your tool hands, causing skinned knuckles or broken finsers. Check time tools should always be in a when stored is if it is Vou not in use. you have a well-organized should be will save a lot of tool chest. Each tool clean, and ready for use (Figure in its place, 2-5). Follow these basic rules for safe hand tool use. 1. When using any hand tool, keep your hands and the Grease and tool clean. can cause the tool Any 2. slip oil on the to slip or tool or your your hands hands to slip off. can cause injury When using a screwdn\er to tighten or loosen a screw, make fits snugh sure that the blade of the screwdriver in the screw head slot. .\ blade that is too damage and disthe screwhead slot. .-^ screwdriver of the wrong can slip out and cut you. The top drawing of small will twist, and consequently tort, size Figure 2-6 show tip. s the use of the proper screwdriver In the center drawing, the screwdri\er tip wide and w ill the screwdriver is 3. Figure 2-5. Keep your tools clean and organized. (Ford Motor Co.) will happen when a used. Always use a screwdriver with lar to the slot it and cause damage. The bottom drawing shows what tip is too not held straight up, the blade tip will slip out of the screw slot rounded is scar the area around the screwhead; its length perpendicu- of the screw (Figure 2-71. This allows the tip to be fully seated, lessening the chance ot slipping. . UNIT 8 2: Safety in Shop the Motorcycle Figure 2-8. Never hammer on a hardened surface, such as another hammer. (Snap-On Tools Corp.) Figure 2-7. Hold the screwdriver straight up from the screw. Steady the tip with one hand and make sure the shank is perpendicular to the screw head. (Hand Tool Institute) 4. Use a pry or pinchbar screwdriver. not bending A —with may not use a designed for turning, is pressure, a screwdriver shank will bend. Also, since the hardened to keep Do for prying. screwdriver it of the screwdriver blade tip from wearing, it is brittle is and break, increasing the possibility of eye injury. If you must use a screwdriver for light prying, be sure you select one that is heavy enough to take the strain, and always wear safety glasses. 5. Do not carry screwdrivers, chisels, or open sharp- Figure 2-9. Use the hammer correctly. Grasp at the end of the handle as shown and hit squarely. (Ford Motor Corp.) edged tools in your pockets. If you carry sharp tools in your hand, carry them with their cutting edges downward. Do not run while carrying any kind of tools. In fact, 6. never run in the shop! Before using any hammer, make sure that the head securely attached to the handle. head can 7. Never fly off its A loose Never is hammer handle and cause serious injury. 10. hammer another strike and will splinter into ily put out an eye or steel particles that inflict To use a hold properiy. Grasp the its it hammer is brit- could eas- you must learn how hammer handle and place the head of the hammer on Tap you the object once or twice lightly, and then, are sure of your aim, hammer on the object square with the full striking force of the 9. hammer (Figure 2-9). Always hit with the striking face of the hammer. fit the bolt bones. the the object. Hit to skinned or bruised knuckles, and possibly broken to when wrench wrench for inch-size bolts and nuts; use a metric wrench for metric fasteners. If the wrench slips, you face the danger of personal injury in the form of near the end of object you want to strike. This will help your aim. select the correct-size wrench with an opening considerably larger than you stand a good chance to round off the comers of the nut or bolthead. Use an inch-size some other wound. Wear efficiently, Always the nut, eye protection when hammering. 8. hammer a any hammer with (Figure 2-8). Hardened steel tle side (cheek) of the or nut you are working on (Figure 2-11). If you use strike a hardened-steel surface with a steel- headed hammer, and never strike with the (Figure 2-10). 1 1 When using open-end wrenches, always pull the load (Figure 2-12). Pulling slips or breaks, because usually it is away from some is much safer when you pull if a obstruction. If something wrench often toward an obstruction which could your hand and knuckles 2-13). if the wrench it is you push it, jam slips (Figure HAND TOOL SAFETY Figure 2-13. If you push a wrench, espetowards an obstruction, you may jam your fingers. (Sears, Roebuck and Co.) cially WRONG Figure 2-10. Never cheek of the strike with the side or hammer head. (Hand Tool Insti- tute) WRONG RIGHT Figure 2-11. Use the correct size wrench: jaws must fit the nut or bolthead exactly. (Sears, Roebuck and Co.) Figure 2-14. Correct method of pushing on a wrench. (Ford Motor Co.) Figure wrench 2-12. Pulling on an open-end safer than pushing it. (Ford Motor is RIGHT Co.) 12. If you must push an open-end wrench toward an obdo not wrap your fingers around the han- WRONG Figure 2-15. Use an adjustable wrench so that the pull is on the fixed jaw, not the movable jaw. (Sears, Roebuck and Co.) struction, dle. Use the heel of your hand, as shown in Figure 2-14. 13. When snugly against the flats of the nut or bolthead, and then pull the wrench toward you, with the fixed jaw using adjustable-end wrenches, observe the same precautions you would observe when using dinary open-end wrenches. Adjust the jaws to orfit doing the pulling. able jaw, and if If you the pull try to pull is with the adjust- too heavy, you off the adjustable jaw (Figure 2-15). may snap 9 UNIT 10 2: Safety in the Motorcycle Shop Do well as for bare wires. and never use electrical on a wet or damp 2. not use a defective tool, power tools while standing floor. Before turning a machine or electrical tool on, check to see that all safety guards are in place adjusted. 3. Figure 2-16. Pliers bolthead. (Sears, will damage a Roebuck & let it Co.) down sure the switch with the power nut or tie and properly or block a safety guard! Before you plug in any machine or electrical tool, make NEVER Never come ments. to a is off. If the off. Make machine or all adjustments tool is running, dead stop before making any adjust- When you are through, turn are doing any power grinding, chipping, or it off for the next person. 4. If you sanding, always wear eye protection. In general, wear eye protection around machines and power tools. 5. HAND IMPACT POWER When using power equipment on a small part, never hold the part in your hand because ways use locking Figure 2-17. Socket wrenches: left, impact; center, hand; right, power. (Snap-On Tools 6. Corp.) When pliers or a operating a to be drilled. Use drill press, either a it could slip. Al- clamp. firmly secure the item clamp or a vise (Figure 2-18). 14. Never use a pair of pliers as a wrench, because you damage the bolt head or nut (Figure 2-16). Sometimes, with caution, you can turn a bolt or nut 7. Do not use more extension cords than necessary; use will without damage 15. 16. if it is Always replace sockets When you sockets on use socket loose. that show cracks or wear. wrenches, never use hand '-<-^ power or impact wrenches. Figure 2-17 shows the difference between hand sockets and power and impact sockets. Hand sockets are nickel plated; power and impact sockets are made of black metal. Select the right-size socket for the job, and select only heavy-duty impact sockets for use with air or electric impact wrenches. 17. When using files, VICE USED TO SECURE OBJECT always use a handle on the end. This gives a good grip and avoids end into your hand. Never pry with a and breaks tail jamming the file: it is brittle easily. POWER TOOL SAFETY Power tools are tools ity, air, which get their power from electricUse power tools only after you or hydraulic fluid. have received proper instructions on their use from the apFollow these rules when using power propriate source. tools. 1. If you that are using an electrical it is properly grounded. power Some tool, make sure electrical tools are double insulated and do not require separate grounding. Check the wiring for cracks in the insulation, as TWO C CLAMPS USED TO SECURE OBJECT Figure 2-18. Always secure the object to drilled, especially a small object. (Top: Hand Tool Institute. Bottom: Sears, Roebuck be and Co.) . FIRES the electric outlet nearest the work sure that they working and correctly positioned. are 9. string When working you Always grasp FIRE PREVENTION the air hose firmly —sometimes 11 may it kick or shake around. Never kink an air hose to cut off Always use machine guards, and make 8. Never area. pathways. electric cords across AND with a hydraulic press, make pressure. When using compressed air to inflate a face and body sure that are applying hydraulic pressure in a safe manner. Stand to the side, and remember to wear eye protec- away from event that the tire turn your tire, the tire to protect yourself in the explodes. Special safety inflation tire containers or cages are available to hold tires while they are being inflated. tion. Do 10. not touch any moving machinery parts. Remem- FIRES ber that loose clothing can be dangerous around run- ning machinery or tools. Never 1 1 try to down slow part or tool with your stop of If the 12. its own or brake a moving machine hand or other device. Let it machine or power it tool starts to smoke or make off immediately. FIRE PREVENTION know all else, occurs where the fire fires fire they will put out. Figure 2-19 shows some typical signs that are used to hoses, and location of portable fire extinguishers, By alarms. fire Also, signs and printed in red. fire law, such signs need to be fire equipment must be prominently located and easily accessible. Some shops have Never walk away from a running machine or power tool. Always turn it off when leaving the area or the people in the area, pull the alarm box, and call the fire when department. Because of the existence of combustible liq- the job is completed. uids, such as oil COMPRESSED AIR CLEANING AND PARTS serious. solvents to clean parts. gasoline because of the danger of fire Never use or explosion. When using cold or dip tank cleaning solutions, be sure to wear eye protection, gloves, and a shop apron. Compressed air is a very common source of injury. Always check the hose before using compressed air, because a badly worn air hose will burst under pressure. Replace a worn hose to prevent accidents. Check the air gauge; compressed air fire. Never You when the gun is if it is Class A: Using compressed may dangerous. For example, if pointed directly bearings is extremely compressed air, you will spin it ten times faster than it would ever rotate inside the hub. This can cause the bearing to shatter and fly apart like shrapnel. Bearings should be cleaned in solvent and placed on a clean shop psi of towel to air-dry. Avoid using compressed thing clean. If you do use respirator. Whenever air, air to possible, use a solvent uum instead of blowing parts clean. Do not use compressed air to clean performing a brake job. There is blow any- wear eye protection and a wash or vac- brake parts when always the possibility that harmful asbestos dust will be blown out. Always use a washer or vacuum to clean brake assemblies. the shop can be be evacuated, leave they are not blocked off by any Act immedi- fire! Class A fire extinguishers are for ordinary wood fires. The fire extinguisher HOSE clogged. Never you spin a wheel bearing with fire exits if fire in to warn FIRE be forced into your skin or eyes. air to spin-dry shop needs paper and use compressed air to clean your clothes or parts of your body. Foreign matter and gasoline, any fire, All portable extinguishers are marked by class as fol- should especially never look into the discharge nozzle in order to find out alarm box. In case of lows. should never be over 30 pounds per square inch pull the trigger fire (Fire exit signs are printed in black.) ately to contain (psi). toward anyone. a In case the through the marked the Use only recommended 30 before a extinguishers are and what types of identify the accord. a strange sound, turn 13. Before AND Te^J UNIT 12 2: Safety the Motorcycle in Shop ^ ^ FOR USE ON ^TEXTILES ETC { FOR USE ON J FOR USE ON FOR USE ON FOR USE ON ^^WOODPAPER-^a iTEXTILES ETC.^ LS'GREASESI PAINTS-l ^^ELECTRICAL^ SHOWN IN •GREASESj l-PAINTS- ggELECTRICALES ELECTRICALl EQUIPMENT^ MiEQUIPMENTgJ^y USE Figure 2-20. Fire extinguishers are always marked by class: Class A, B, C, or a combination of classes. A Class B fire extinguisher is shown at left. (Industrial Safety and Security Co.) must cool and quench the Class B: "A" an is B Class The marking fire. in a triangle. extinguishers are for fires caused fire by flammable liquids such as line. The fire smother the oil and gaso- extinguisher must blanket or The marking fire. is a "B" in a rectangle. Class C: C Class by extinguishers are for fires caused fire faulty electrical equipment. The 'Mi fire extin- guisher must use a nonconducting agent to put out the "C" in a of the above kinds of fires The marking fire. a is I circle. In the motorcycle shop, all are possible. Normally, therefore, all three classes of fire Figure 2-21. extinguishers are available. Figure 2-20 shows the class markings used on You extinguishers. fire oughly familiar with these so that there A multipurpose Class extinguisher is commonly used cycle shop. (Walton Kidde, Kidde, Inc.) should be thor- can never be any ABC fire the motorDivision of in doubt as to which extinguisher to use. A multipurpose class ABC fire extinguisher is shown motorcycle shop because they can handle of fire that may occur In case of a 1. 2. Pull the fire alarm, none, 7. if call the fire there is one in the shop; 8. if If the fire is small, try to put it 9. out with the appropri- Never use water or a class 5. B or C fire fire hose on a extinguisher If the fire is large, is fire leave the shop by the exits if they are not closed by for which a required. fire. fire In any case, evacu- firefighters requested. do not In case of a large fire, Never return ventilate the area. Close fire from spreading. to a burning building for anything. Your too valuable! Ventilate the area after the fire is out. GASOLINE AND LIQUID FLAMMABLES Never put water on a gasoline fire. marked if life is there department. Help the Direct firefighters to the area. doors and windows to prevent the in the ate fire extinguisher. 4. 6. only follow these steps. not attempt to fight a large fire with portable fire extinguishers. there. Immediately warn other workers and students shop of the fire. is 3. fire, three classes all Do ate the area immediately. in Figure 2-21. These extinguishers are recommended for the Instead, use a class smother the flames. ment first A B good and then attempt fire. or Water ABC rule is fire just spreads the extinguisher to to call the fire depart- to extinguish the fire. But if it BATTERY SAFETY gets too hot or too smoky, get Never go back out! 13 into a burning building for anything. If you have to fight a gasoline fire, guisher low at the base of the until you are positive that reignite very quickly if is it aim the fire extin- and stay with the fire out. Gasoline vapors can fire you do not get the fire thoroughly snuffed out. The important remember about gasoline fact to liquid gasoline itself is is that not the real danger. Gasoline va- pors are. So to avoid gasoline fires and explosions in the shop, you have to prevent gasoline vapors from escaping. The vapors are heavier than air and settle in low spots on where a lighted match or cigarette, or even an from an electric switch or motor can ignite them. Figure 2-22. Gasoline should be stored a safety can. (Eagle Manufacturing Co.) the floor, arc Gasoline vapors may by the movement of in be carried a considerable distance air. Vapors are often ignited by a source such as a space heater or a pilot light on a water heater located at some distance from the gasoline source. Avoid the buildup of gasoline vapors in the shop, even if you think there are no sources of ignition. Follow these rules when handling gasoline or other flammables. 1. Of primary importance, gasoline should be used only as a source of energy for a gasoline engine. should It never be used for any other purpose. 2. Never use gasoline to clean anything, including Figure 2-23. Oil, gasoline, and solventsoaked rags should be stored in a metal oil waste can with a lid. (Eagle Manufactunng your hands. Kerosene or high-flashpoint solvents designed Co.) for cleaning parts should always be used to clean and tools only. Vaporized gasoline can parts and 3. flash ignite back to the container you are using. Clean up gasoline immediately. spills If 8. gasoline line is ance pilot smoking or spark, including the use of electric switches, until you get up with Small rid of the vapors. rags, spills can be wiped which then should be disposed of approved container. Large spills should be in 9. an pump cut electric fire island, shut off the power department. at the Do 5. Perform fuel such as at the When in a well- draining the carburetor or a to dry away from any source of igThe vapor can catch fire and the liquid can cause skin 7. irritation. Store gasoline only only in and solvents, in all no approved metal cabinets heat. Never pour flam- down the drain! When oily rags are lying about, they could help start a oily rags fire. Also, can ignite by themselves by spontaneous BATTERY SAFETY The storage battery is potentially one of the absolutely necessary and an approved safety can (Figure 2-22). most danger- ous items around the shop. Normally, but especially when being charged, batteries give off explosive hydrogen gas that can be ignited by a flame or spark (Figure 2-24). Moreover, battery electrolyte when Obey signs. combustion. and allowed nition. cigarette, appli- Store oily and gasoline-soaked rags in an approved left department. Gasoline-soaked clothes should be removed immediately lit electric switches. metal container (Figure 2-23). to fuel line, catch the gasoline in a container. 6. 10. call the local system work only outside or ventilated area. gaso- emergency switch pumps, and fire and away from any source of not flush gasoline into the street without approval of the ignition, including a lights, that gaso- allowed to vaporize around mables or combustible liquids If there is a large gasoline spill, line if Store flammables other than gasoline, such as paints, thinners, thor- oughly flushed with water. 4. can be dangerous any source of open the doors and windows get plenty of ventilation. Avoid any source of fire spilled inside the shop, to Never smoke around gasoline. Remember is an acid solution that can cause damage to eyes and skin, as well as to clothing. The primary rule is to avoid any source of fire around batteries. . 14 UNIT Safety 2: In the Motorcycle Shop ^/^ Keep open flames and sparks away from a not smoke when charging a battery. 12. battery. Do Turn off the charger before disconnecting 13. its leads (wires) to the battery. Replace the 14. RIDING A cell covers before moving a battery. MOTORCYCLE You must take extreme care the shop. You must when riding a motorcycle in be particularly careful about other workers (and customers) Ride slowly, care- in the shop. and get someone to guide you fully, THE SHOP IN if you cannot see a certain area or spot. Never take it them before test Figure 2-24. Storage batteries give off a highly explosive hydrogen gas, especially when being charged. Keep all fire or sparks away from the battery area. (U.S. Navy) very which you cannot see, smell, or taste. It does not take much carbon monoxide to kill you. Whenever you have an engine operating inside the shop, be sure cigarette, cigar, or pipe, an open flame, and to attach flexible exhaust hose to the bike's exhaust The exhaust hose should pipes. lit Always starting a customer's motorcycle. Exhaust gases contain a deadly poison, carbon monoxide, one end of a including a for granted that the brakes work. lead outdoors or to the shop's ventilation exhaust system. Even if you are working sparks from grinding or welding. Follow these precautions outdoors, you shouldn't work around the exhaust pipe for when any length of time while the engine 1. servicing batteries. Wear chemical goggles and neoprene gloves when servicing batteries. arm's length when removing battery caps. 2. Stand 3. Handle the battery and at its acid with care. Wash im- mediately any part of your body or clothing that comes in contact with battery acid or corrosion. If you get acid in your eyes, they should be washed with water for 15 minutes and you should immedi- Do Compressed air: air under pressure, used power tools, and to spray paint. Eye protection: tect the mechanical connections. the battery as to fill tires, to safety glasses or a face shield used to pro- eyes from hazardous substances or objects. Fire extinguisher: a portable device designed to put out a fire. when making electrical or Keep your head and body much as possible in case of not lean over batteries away from operating. KEY TERMS ately consult a physician. 4. is explosion. Hand tools: tools that are Power guided and operated by hand. powered by tools: tools electricity, compressed air, or hydraulic fluid. Safety shoes: protective shoes with steel-capped toes. 5. Use proper instruments 6. Avoid for testing a battery. overfilling a battery, especially if it Storage battery: a device that uses chemicals is to be to create and store electrical energy. charged. 7. Use water and baking soda (a neutralizer) to clean off the top of a battery. 8. Wash your hands immediately after handling a bat- CHECKUP 1 9. 10. Wear a face shield Provide good when using ventilation a battery charger. when using a Remove 2. 3. protective clothing should you wear for general Why is it a good idea to wear eye protection shop? the cell covers before charging a battery, unless the instructions for the covers say otherwise. What safety in the shop? battery charger. 11. Describe two items of personal appearance which can affect safety. tery. 4. Why should hand tools be kept clean? in the DISCUSSION TOPICS AND ACTIVITIES 5. when using a screw- hammer never be used to strike a har- List three precautions to follow driver. 6. Why should a Explain Class A, B, and 14. List nine steps to follow in case of fire. 15. List ten precautions to follow dened-steel surface? 7. Why is it Why safer to pull rather than push on an open- 9. Describe three precautions to follow 16. What are the two main dangers when handling bat- when using 17. Explain how to safely ride a motorcycle in the shop. when using DISCUSSION TOPICS AND ACTIVITIES equipment. 10. List two dangers involved 11. Why should compressed 12. when handling gaso- tools? electrical parts extinguishers. teries? should you wear eye protection power fire line. end wrench? 8. C 13. 15 in using compressed air. 1. Develop a safety checklist all when doing What can happen dirt off air not be used to clean tor. a brake job? 2. if you use compressed your clothing? air to blow for your shop area. Call unsafe conditions to the attention of your instrucCorrect any hazards you find. Make a safety inspection of your and correct any hazards you find. home work area iT^lmost all motorcycle repair operations require the use of hand or power-operated tools. Expert motorcycle crafts- men know their tools. as they do, know They know how and why they work how to take care of them. In common tools used on most shows a set way the correct and know to use them, this unit we shall describe the repair operations. Figure 3-1 of basic hand tools cycle maintenance and repair. commonly used The many in motor- special tools re- quired for specialized service jobs will be described in the sections on the TOOLS specific servicing procedures. JOB COMPETENCY OBJECTIVES When you be able 1. 2. finish reading and studying this unit, you should Describe the types and uses of screwdrivers. and Identify explain the of uses Recognize and describe the uses for the of 4. Explain the operation of a parts cleaning tank. 6. Demonstrate the the ability to find specifications in a common SCREWDRIVERS common types The purpose of pliers. a screwdriver loosen and remove, Describe the correct hammer to use on shop service manual. wrenches. 3. 5. to: different ser- is screws. screwdrivers are required for vicing procedures. to drive and tighten, or to Many sizes and types of the many types of screws found on motorcycles. ADJUSTABLE NEEDLE NOSE PLIERS LOCKING DIAGONAL JOINT PLIERS PLIERS SLIP NOSE PLIERS PLIERS ^^t^^ SCRAPER METRIC SOCKETS ,.^^^=^ _-£^^g^ SOCKET EXTENSION UNIVERSAL SOCKET SPEED HANDLE FLEX HANDLE '^^ d ADAPTER RATCHET ~-ic FEELER GAUGES h BOX END WRENCHES ^ *^ ^ hi B y PUNCHES il o CHISELS Sf Tf inii UUMBINATION WRENCHES SLOT SCREWDRIVERS PHILLIPS ALLEN (HEX) WRENCHES Figure 3-1. Hand tools commonly used in motorcycle work, (Stanley-Proto In- dustrial Tools) 17 UNIT 18 3: Tools Standard screwdriver Special-purpose screwdrivers The standard screwdriver is used on screws and bolts with slotted heads. The part you grip and turn is the handle. The At steel part the extending beyond the handle end of the shank is screwdrivers, the blade is the shank, and the blade (Figure 3-2). In standard is ground flat. Some screwdrivers have a round shank, others a square shank. The convenits wood or plastic handle and slim tional screwdriver, with shank, steel ing force — is designed to withstand a great deal of twist- but only in proportion to its first glance, ilar to Phillips cross-slot screws are sim- find that they are different and require a different type of Reed and Prince screwdriver. For one thing, the deeper and the walls separating the ure 3^ driver. compares a Reed and Prince with a Phillips screwto Clean the slots when using Reed and into fit deeper screw head. The screw heads are shown usual slots are slots are tapered. Fig- Note the sharper point designed in the figure. size. Standard screwdrivers are sized by shank diameter and Reed and Prince screws, but, on close examination, you will the at the left and use more pressure than Prince screwdrivers. length. A commonly used standard screwdriver in motorcycle work has a Vie" blade and a 4" shank. The square-shanked screwdriver is sometimes used with a wrench or locking pliers for additional leverage. The wrench or locking pliers are fitted to the square shank and used to help turn the screwdriver. Take care not to use excessive force in turning since the fastener or the screwdriver blade may be damaged. You should never use an ordinary pair of pliers since they will slip and mar the PHILLIPS screwdriver shank. REED AND PRINCE SHANK BLADE Figure 3-2. Parts driver. (U.S. Navy) of a standard HANDLE Figure 3-4. screw- Reed and Prince compared to a The Reed and Prince has a much sharper point. (Hand Phillips (top) (bottom). Tool Institute) Clutch screwdrivers are made for turning screws of the Phillips screwdriver clutch-bit type (Figure 3-5). These screws are also known as "figure-eight" or "butterfly" screws. Like Phillips and The Phillips screwdriver shaped slots is designed to fit into the cross- of a Phillips screw. Figure 3-3 shows a Phil- lips screwdriver. The cross-shaped screwdriver tip its head. The a screw with an x-shaped slot in into fits Phillips screw was developed to prevent a screwdriver from slip- ping out and scratching a polished metal or painted sur- For face. this reason, many motorcycle components are come tached with these screws. Phillips screwdrivers sets, grouped by length and size of blade. The blades Reed and Prince screws, clutch-type screwheads signed to keep the bit are de- from slipping off them. There are many variations on the Prince, and clutch screwdrivers. Many Reed and Phillips, manufacturers use one or more of these different types of screws in parts that they do not want the consumer to tamper with. You have at- in are sized on a numbering system from zero to six, zero being the smallest Phillips and Numbers two and three commonly used in motorcycle six the largest. screwdrivers are work. 4" CLUTCH HEAD (NEWSTYLE, TYPE Figure 3-3. Phillips screwdriver phillips-head screw. (U.S. Navy) fits into a CLUTCH HEAD A) (OLD STYLE, TYPE G) Figure 3-5. Clutch-type screwdriver screws. (Hand Tool Institute) and WRENCHES REED & PRINCE PHILLIPS TORQUE SET TORX POZIDRIV HEX SOCKET SLAB BRISTO 19 (ALLEN) Figure 3-7. An impact driver is used to loosen or tighten very tight screws. (Snap- On Tool Corp.) wrenches are the most conmion tools found motorcy- in a cle technician's tool box. CLUTCH HEAD SCRULOX (NEW STYLE, TYPE (ROBERTSON) Wrenches CLUTCH HEAD A) (OLD STYLE, TYPE G) to (Hand Tool Institute) have a special screwdriver for these special screws. A selection of these different types of screwdrivers with their shown in Figure 3-6. There are many screws on the typical motorcycle engine which are too tight to be removed by any of the foregoing special screwheads screwdrivers. An is impact driver (Figure 3-7) addition to a motorcycle mechanic's tool is is a valuable This device used with screwdriver sockets. The correct-size socket installed is on the end of the impact driver, and the screw- driver tip is kit. is placed in the screw slot. A ball pein hammer A cam then used to strike the end of the impact driver. action device inside the impact driver causes a turning tion when the hammer strikes the made and in different sizes to nuts. The size of a fit the different wrench usually is stamped on the wrench end or handle. A fraction is stamped on if the size of the wrench is given in the inch Figure 3-6. Different screw designs require different screwdrivers. are sizes of bolts mo- system; for example, V\6 indicates V\6". number, such as is A whole digit wrench 12, indicates that the size of the given in metric: 12 indicates a size of 12 millimeters. Some metric wrenches will have indicating 3-8 has 14 stamped on the that "mm" by the "millimeters." The wrench shown it. number, in wrench measures 14 millimeters across the flats and it will fit on a bolt head or nut that measures 14 milli- meters across the flats. 14 MILLIMETER DISTANCE ACROSS FLATS impact driver. The tool can be adjusted to loosen or tighten a screw. The combination of impact and twisting will usually loosen the 14mm most stubborn screws. WRENCHES Wrenches are used to hold, grip, and turn nuts and There are many different types of wrenches. In Figure 3-8. The wrench size is stamped on In this case a 14 represents 14 millimeters, the distance across the flats of the handle. bolts, fact, Figure This means that the opening of the jaws. UNIT 20 3: Tools Open-end wrench The open-end wrench (Figure 3-9) has an opening at each end of the handle which fits over a bolt or nut. The opening is usually at an angle of 15 degrees to the handle, which makes turning in a tight space easier. Open-end wrenches are made in many different sizes and shapes; most have two open ends of different sizes. Figure J-9. An open-end wrench. (Snap- On Tool Corp.) Figure 3-12. Sets of wrenches. The socket sockets or socket on a handle for fits turning. (Klein Tools, Inc.) ing them tight. At the other end, there is an open-end wrench for fast turning. Each end is at a 15-degree offset to the handle, allowing the wrench to clear obstructions POINTS (12) when end its is box end is used. The 15-degree angle on designed for turning in the open tight spaces. Socket wrench Figure 3-10. A box-end wrench with a 15degree offset and 12 gripping points. (Snap- Box-end wrench term socket wrench The box-end wrench, or simply, box wrench (Figure 3-10) is made to fit nuts and bolt heads so that they will not slip off. These wrenches are usually two-ended, with size openings different- on each end. Frequently box wrenches are or 15-degree offsets. Figure 3-10 made with 10-degree shows a wrench with a 15-degree openings have 12 gripping This is degrees slots, offset. Box wrench or points, for the nut. an advantage, since a handle movement of only 30 is needed to get a The socket wrench (Figure 3-12) is an improvement over the box wrench in that it will not slip off nuts or bolts and it can also be turned much faster with the aid of several types of handles. Socket wrenches are made in many different sizes to fit the many sizes of bolts and nuts. The new bite when turning. Combination wrench The combination wrench (Figure 3-11) has two types of openings, both of the same size. At one end of the handle, there is a box wrench for breaking tight nuts loose or pull- Sn,} p. is often shortened to socket in common usage. Sockets are attached to their handles by a square hole one end (Figure 3-13). These drive holes are made ferent sizes. For small bolts and nuts, socket sets at in dif- with a V*" square drive are useful. For general-purpose work, a %" drive set socket set; is popular. Heavier and there are even for very large nuts Sockets are and work %" and requires a Vi" drive 1" drive sets, made bolts. made with different numbers of points. Fig- ure 3-14 shows sockets that have six, eight, and 12 points. The more points a wrench has, the easier it is to slip it on a bolt or nut. More points also give a better grip when turning. The fewer the points, the more metal there is in the socket to support the bolt, and thus the stronger the socket is. Sockets with fewer points do not grip as well, i© Figure 3-11. Combination wrench. (Snap-On Tool Corp.) WRENCHES 21 Socket drivers Various handles or drivers are used They drive size to turn the sockets. and with different- are available in different lengths ends. Handles with and Vs", 'A", drive Vi" ends are commonly used. commonly used Ratchet handles (Figure 3-16) are drive sockets. The to drive end of the ratchet snaps into the As mentioned, drive end of the socket. different-size drive ends are available. The ratchet handle moves back and forth to drive the socket. SOCKET END When the ratchet catch one direction, pulling the handle in is snapped will result in a tighten- ing action and pushing the handle will simply return DRIVE END Figure 3-13. Socket wrench— 12 points are shown on the socket end (left): a handle fits into the square hole of the drive end (right). starting position without putting force its the socket snapped from the nut or bolt. When to it on or removing the ratchet catch be in the opposite direction, the result will is re- versed: pushing the ratchet handle will loosen the nut or and pulling the handle bolt position. This action Figure 3-14. Sockets can have a different number ets of points; 6-, 8-, are shown. however, and require bite. (Stanley-Proto a greater handle Most sockets have back to its starting 3-17. and 12-point sockIndustrial Tools) new it ^:b==?ii 12PT. 8 PT. 6 PT. will bring illustrated in Figure is movement DRIVE END Figure 3-16. The ratchet handle is a common socket wrench driver. (Snap-On Tools to get a Corp.) eight or 12 points; six-point sockets are used for heavy duty. Sockets are available in long or short lengths. Long sockets are used for removing long, threaded parts such as PULL spark plugs. Most standard bolts and nuts can be loosened with a short or shallow socket. A deep and a shallow socket are compared in Figure 3-15. Some CATCH sockets are designed to be used with air or electric power. Sockets designed for use with impact wrenches are made of heavier material than those operated by hand. RATCHETING Only those special impact sockets can be safely used on power equipment. They can usually be identified by their dull gray finish in comparison to the bright chrome used on hand wrenches. DEEP SOCKET WRENCH RATCHETING V RATCHETING Figure 3-17. Ratchet (Ford Motor Co.) Ratchet handles Some come handle in a variety operation. of sizes and lengths. are available with a swivel end to help get into ob- structed areas. A selection of ratchet handles is shown in Figure 3-18. A large number of socket wrenches. shown in crank and SHALLOW SOCKET WRENCH Figure 3-15. Shallow wrenches. (U.S. Navy) and deep socket A other handles Figure 3-19. is is available to drive typical collection of attachments A speed handle is shaped is like a used to speed up the process of removing or installing a nut or a bolt. The breaker bar has a hinge that will permit driving at different angles. Its long handle lets the mechanic use a good deal of force to loosen a tight nut UNIT 22 Tools 3: ^ 351^^3 «Sfc 5P ^^^^ 3 ALLEN HEAD SCREWDRIVER SWIVEL Figure 3-18. Different styles and sizes ratchet handles. of (Snap-On Tools Corp.) ADAPTOR EXTENSION BREAKER UNIVERSAL Figure 3-20. Tools that can be driven by socket wrench handles. (Snap-On Tools BAR^g?^^^ Corp.) ^ SLIDING T-HANDLE %' Figure 3-19. Socket drivers ments. (Snap-On Tools Corp.) and attach- TORQUE SCALE The or bolt. to slide to An sliding T-handle will allow the socket driver any position along the handle. extension is also shown Figure 3-19. Extensions in are used to lengthen the distance the socket wrench. One end of They between the handle and the extension driver, the other to a socket wrench. are also is amount beam deflected. is used to connect sockets with attachments of dif- nician that the bolt or nut shown in head and screwdriver sockets are availsocket handles. The universal joint attachment permits a socket to be attached and driven is to at an angle Another type of torque scale allows the motorcycle technician to adjust the to a certain torque setting. where space used of torque. ratchet drive head. Its adjustable handle and An is Torque ferent sizes. Allen able for the wrench has a Figure 3-20. collection of these is amount (Stanley-Proto Industrial Tools) The extension allows Other tools besides sockets can be driven by socket driv- adaptor tighten parts to the correct where an ordinary handle would not have enough room to turn. Extensions shown in Figures 3-1 and 3-12 (bottom). A Figure 3-21. A torque wrench connected to a handle or is the socket to be used in an area ers. HANDLE are available in different lengths. most is measured common A is wrench clicking signal tells the tech- tightened to that torque. several different systems. in The English system units are foot-pounds and inch-pounds. There are 12 inch-pounds in a foot-pound. In most common torque measurements Newton-meters or meter-kilograms. Figure 3-22 shows the metric system, the limited. are Torque wrench torque wrenches with different scales. Recently, computer technology has been applied to the Torque Many is the word applied motorcycle parts must be tightened to exactly the correct amount of torque. The wrench used to the correct torque One common 3-21, to a turning or twisting force. is is to tighten parts called a torque wrench. type of torque wrench, shown beam on the wrench bends in Figure as the resis- tance to turning increases. The pointer lines up with different readings on a torque scale to show is It a torque wrench with a the torque, or the built-in microprocessor memory. has a pressure-sensitive keypad and a digital on the As a fastener window. There mode in readout. equipped with a beam-and-pointer assembly. Dur- ing tightening, the torque wrench. The electronic torque wrench (Figure 3-23) is tightened, the torque are three operating which the torque is in which lected torque is a (LCD) displayed modes: a display shown, a memory mode which the highest torque applied mode is is in shown, and a signal buzzer sounds automatically when the se- reached. WRENCHES Figure 3-22. Inch-pounds or foot-pounds are used on English-system torque wrenches; Newton-meters or meter-kilograms are used on metric-system torque wrenches. (Sears, Roebuck and Co.) HEX (ALLEN) WRENCH AND SET SCREW HEX WRENCH SET (ALLEN WRENCHES) 3-23. Electronic Figure (Sears, Allen Some Roebuck and torque (ALLEN WRENCHES) wrench. 3-24. Allen-head or hex key Figure wrenches. (Top: Sears, Roebuck and Co. Bottom: Stanley-Proto Industrial Tools) Co.) wrench parts of a motorcycle are connected with Allen head screws. Special Allen wrenches are provided to deal with them. The head of the screw has a hexagonal (six-sided) hole. Allen or hex wrenches are also hexagonal, with one in Figure 3-24 (top). long arm and one short arm as shown More leverage wrench is into the obtained by inserting the short arm of the screw head, but you must be careful not to strip the threads or break the or hex keys often come in screw of the wrench. Allen a set, as shown in Figure 3-24 (bottom). Both metric and English system screws and wrenches are used. Try different wrenches until one fits. Adjustable-end wrench The wrench shown in Figure 3-25 is called an adjustableend wrench. The jaws of this type of wrench are adjustable Figure 3-25. Adjustable-end wrench. (Top: L/.S. Navy. Bottom: Hand Tool Institute) 23 UNIT 24 3: Tools within their designed limits. When using adjustable-end wrenches, you must be careful to observe the same precautions you would observe when using ordinary open-end wrenches: (1) adjust the jaws to fit snugly against the flats of the nut or bolthead, and (2) pull the wrench toward you, with the fixed jaw doing the pulling. Once the nut or bolt wrench you is turning, to continue the turning. flop the wrench around the nut or to bolt. you may "flop" the Keep checking each time be sure that the jaws Remember with the adjustable jaw, and the pull that if is still fit you snugly try to pull too heavy, you may snap off the jaw. Adjustable wrenches vary from about 4" to about 20" The longer length. to opening. the the wrench, the larger For example, a is in the adjustment typical 6" adjustable wrench opens about y/ wide, while a 12" wrench opens about I'/ie" wide. WRONG CORRECT Air impact The Figure 3-27. Combination or wrench Sears, impact wrench, or simply, impact wrench (Figure 3-26) is used to loosen large nuts and bolts which are very air tight. Hand (Top: ers. Tool Roebuck and slip-joint Institute. pli- Bottom: Co.) Impact wrenches are power driven, usually by com- pressed air, although some are electrically driven. They brate or impact up and a control on the down driver, the as they loosen. By wrench can be used vi- reversing for tighten- heavy-duty impact sockets must be used with impact wrenches. The torque on some impact wrenches can be increased or decreased at will. Impact wrenches can ing. Special save time but can also cause damage to parts if they are allowed to overtighten them. Impact wrenches are best used for disassembly of large components. PLIERS Pliers are an extension of a technician's fingers. many There are types of pliers, and each has a special purpose. They should never be used in place of a wrench to loosen or tighten a nut. A which purpose some other craftsman knows which pliers to use for —and tool will Combination The pliers he or she never uses pliers when do the job better. pliers most commonly used in motorcycle work are the 6" combination pliers (Figure 3-27). joint or fulcrum to allow the jaws to They have a slip open wide enough to grip large diameters and are consequently called slip-joint pliers. Two different adjustments are possible (Figure 27), bottom). objects. Use the 3- large adjustment for holding larger Some combination pliers have a side-cutter ar- rangement for cutting wire or cotter pins. The better grades of combination pliers are made of drop-forged steel and can take a lot of hard usage. Adjustable-joint pliers Adjustable-joint or channel lock pliers (Figure 3-28) have Figure 3-26. Air-operated impact wrench. jaws that (Ingersol-Rand) They are useful for grasping and holding larger objects. can be adjusted to several different openings. PLIERS Figure 3-28. Adjustable-joint pliers. (Hand Figure 3-31. Needle-nose or long-nose Tool Institute) ers. (Hand Tool pli- Institute) with side cutters, while others are bent As hard-to-get-at places. 25 the angles for at right jaws become longer and sUm- mer, more care must be used in handling them. Snap-ring pliers The two major types of snap-ring outside varieties (Figure have jaws (like Figure 3-29. Diagonal cutting pliers. ers (Hand Tool Institute) that close 3-32). pliers are the inside Inside snap-ring and pliers and grip when the handles are closed an ordinary pair of pliers), and outside snap-ring have jaws that open when the handles are drawn how these common: the jaws pli- to- have gether. Regardless of pliers operate, they one thing of each are designed to in safely engage the snap ring to be Snap rings or lock removed or installed. rings are expandable rings which lock parts to shafts. Essentially, they are very powerful springs. If not handled with the proper tools and with adequate care, they can fly off their retaining grooves (or whatever else there is to retain even personal injury. them) and Always use inflict severe damage or remove the right tool to or install any part that has the potential for getting out of control. Figure 3-30. End cutting pliers. (Hand Tool Institute) Diagonal pliers Diagonal pliers (Figure 3-29) are made for the express purpose of cutting wires. For that reason, they have hard cutting edges. End-cutting pliers Often grouped with the diagonal pliers are the end-cutting pliers (Figure 3-30). These pliers permit you to cut ^ >.,.f' ^i* 3,% very close to whatever object the wire extends out of. Needle-nose pliers Needle-nose or long-nose slender, tapering jaws pliers (Figure which are useful 3-31) have long, objects. In selecting needle-nose and long-nose pliers for your kit, it is most important perfectly aligned. Some EXPAND EXTERNAL RINGS for gripping small that the tips of the jaws be needle-nose pliers are equipped COMPRESS INTERNAL RINGS Figure 3-32. Inside and outside snap ring (Top: Ford Motor Co. Bottom: Lisle pliers. Corp.) 26 UNIT Tools 3: (Figure 3-33) are compound-lever pliers Locking pliers that are clamped ferent sizes, work. They can be adjusted to dif- and once clamped, they remain locked to the to the CHEEK work after one's hands are removed. The adjustable lower jaw is retracted by an over-center spring when the locking handle is released. Adjustment of the size of the jaw opening is made by turning a screw at the end of the primary handle. Remember that locking pliers do not take the place of wrenches. However, they are often used to hold nuts which have had their comers rounded off by the misuse of over and go wrenches. at its Figure 3-33. Locking pliers. (Hand Tool In- drive on other tools such as punches and chisels. intended quickly be on motorcycle drive to damaged by using the parts. up above the surface with the face of the hamflatten it somewhat. Then turn your hammer —just to The ball pein They it is Parts properly rounded hammer The hammer soft-face (Figure 3-36) has a softer head than hammer. Soft-face to can absorb the force of the impact instead of transmitting can it to the material. The most common wrong type of hammer. soft-face hammers and brass. Use brass and are torted has a face that is square by steel hammers. Rubber mallets made from hammers plastic for tapping and aligning parts that will be hammer hammer the pin until Soft-face plastic, rubber, Ball pein work on head. are by many mechanics. For example, hardened-steel hammers are designed not sticking mer hammers are used to align or adjust parts that might be damaged by a hardened-steel hammer. The important thing to remember is that sometimes you must use a hammer made of material softer than the material you are working with. A hammer made of material softer than the material it is hammering will not damage that material because it HAMIVIERS are often used incorrectly FACE Figure 3-34. Ball-pein hammer. (U.S. Navy) the hardened-steel head of the ball pein stitute) Hammers HANDLE -BALLPEEN Locking pliers harmed or (at right angles) to the end of the handle, with the opposite end of the hammer head (the ball pein) rounded (Figure 3-34). The face of the hammer can be used for normal or light hammering operations. The ball pein is used to form and shape sheet metal or to pein over the end of a pin to form a rivet head, as shown in Figure head from a straight pin, 3-35. strike the Cutting sheet metal with To form end of the pin hammer and a rivet that is chisel Figure 3-35. Using the ball-pein hammer. Works) Support materials to be riveted. Flatten head with hammer Round head with the ball peen. face. (Left: U.S. Navy. Right: Stanley dis- are the softest of SERVICE MANUALS 27 RUBBER MALLET PLASTIC TIP HAMMER SOFT FACE HAMMER Figure 3-37. Solvent parts washer, (Graymills) SERVICE MANUALS The DEAD BLOW HAMMER Figure 3-36. Soft-face hammer. (Stanley- hammers, with the possible exception of leather or raw- The dead-blow hammer, shown ert a filled is is one of the most important tools used doing motorcycle repair, in A service — vicing is necessary on the part. Service manuals also pro- vide step-by-step procedures for doing motorcycle repair. hide mallets. tom), manual manual is used to locate specifications or "specs'" the parts measurements recommended by the motorcycle manufacturer. The technician checks parts measurements against these specifications to determine what kind of ser- Proto Industrial Tools) all service by the technician a type of soft-face hammer good deal of force on an in Figure 3-36 (bot- that allows object. you to ex- The hammer head is The motorcycle mechanic can find specifications and reprocedures in two types of service manual: the owner's manual and the shop service manual. pair with shot to increase the driving force and eliminate rebound. The dead-blow feature makes this hammer espe- Owner's manual cially useful for loosening engine flywheels. An PARTS CLEANING EQUIPMENT owner's manual (Figure 3-38) with any new motorcycle. It ate the motorcycle. In addition, Parts cleaning is an important part of almost every motor- plain the basic is a book usually explains that how comes to oper- many owner's manuals ex- services that should be performed peri- cycle repair job. Parts must be cleaned to determine wear odically typically provide accurately and to prevent dirt from damaging the repair troubleshooting procedures and specifications for common job. maintenance procedures. Most motorcycle components are cleaned in a solvent cleaner like the one shown in Figure 3-37. The cleaning tank is filled with solvent which is pumped through and then out of a nozzle. The nozzle stream is a oil, and sludge. the bike. They also Service manual filter directed over the parts. The cleaning solvent thins and washes away grease, on Manufacturers' service manuals are provided by motorcycle manufacturers primarily for motorcycle technicians service motorcycles. The service who manual covers one model UNIT 28 3: Tools GROUP INDEX Figure 3-38. The owner's manual provides maintenance procedures, and troubleshooting help. (Yamaha Motor specifications, Corp. U.S.A.) of motorcycle in great detail, providing specifications, rec- ommended The maintenance, and service procedures. manual step in using a shop service first is to be sure that you have the correct manual for the motorcycle year and model you are working on. Usually, the paint and trim on the fuel tank will identify the model of the motor- some cycle. In cases, you will have to check the engine or number. The shop service manual will de- frame serial scribe where these numbers and how are located to inter- pret them. Next, turn to the index (Figure 3-39), which lists the areas covered by the manual. If you want information on periodic inspection and adjustment, you turn to Section 2. If you need Of manual differ. to Sec- course, the contents and organization of each Periodic maintenance information the you turn electrical service information, tion 6. form of a chart like the is one shown often organized in in Figure 3^0. The side. The work to be done on it is described under "Remarks." The number of kilometers (or miles) between each service interval is charted to the right. For example, cylinder com- item to be maintained is pression should be checked ters listed along the first (initially) at and every 6,400 kilometers left 3,200 kilome- thereafter. Specifications are also often organized into tables. A engine part tightening torque is specification shown in Figure along the part shown are for 3^1. The left side name torque. table part to be tightened is listed of the table. The thread diameter and shown next, followed by the tightening For example, the cylinder head on the engine in the figure uses a 6-millimeter (mm) bolt which should be tightened to 1.0 meter-kilogram (m-kg), or 7 foot-pounds. It is guide a good idea to use a ruler or piece of paper as a when reading across the chart. Also, write down the Unit: Item km (mi) UNIT 30 3: Tools or nut; also called a socket, this wrench can be attached Pliers: a tool designed to grip objects. to or Phillips screwdriver: a screwdriver with a point blade or tip Torque wrench: a wrench designed used for driving Phillips screws. cycle technician; includes specifications and repair procedures. DISCUSSION TOPICS AND ACTIVITIES 1 Socket handles and attachments: tools used to drive socket wrenches. 2. fits all the way around a bolt Try to identify each of the can find in the shop. Make list a shown by writing the names in 1. 1 2. 3. J-Sl 10 5. 6. 11 7. 8. 9. 10. 11. 12 12. 13. 14. 15. tools you of the most important hand tools for a the spaces provided. 4. common hand motorcycle technician to have. CHECKUP Identify each of the tools to tighten bolts or nuts to a certain tightness or torque. Service manual: manufacturer's manual used by the motor- Socket wrench: a wrench that detached from a handle. on the 13 16. 17. 18. 19. 20. 16 I he motorcycle is manufactured to very precise ances that have to be maintained when it toler- One repaired. is of the most important parts of any motorcycle repair or maintenance job mine wear and is to measuring. Measuring is done to deter- A check parts against specifications. mo- torcycle technician must be able to understand measuring systems and use a number of measuring tools to make accurate measurements. In this unit, we shall describe the English and metric measuring systems and the use of English and metric measuring tools. JOB COMPETENCY OBJECTIVES When you be able 1 finish reading and studying this unit, you should MEASURING to: Describe the units of measurement used metric in the measuring system. 2. Describe the units of measurement used in the English (customary) measuring system. 3. Explain how measuring to convert trie between metric and English units. 4. Demonstrate how 5. Demonstrate how Identify The most common unit of measurement used in motorwork is length. In the metric system the basic unit of length is called a meter, from the Greek word metron, meaning measure. Meter is symbolized by the lowercycle service to use a metric to and English rule. measure with a metric and En- case letter m. glish Vernier caliper. 6. the parts of, how and explain to measure with, a metric and English outside micrometer. Different sizes of units in the metric system are related by multiples of ten (Figure 4—1). This means ters 7. Recognize and describe the uses of an inside micrometer, 8. telescoping gauge and small-hole gauge. Demonstrate how luminous intensity, and sub- temperature, current, stance. to use a feeler meters) equals 1 hectometer, and 10 hectometers (1,000 meters) equals a kilometer. gauge to measure the space between two parts. me- that 10 equals a unit called the decameter, 10 decameters (100 larger units Still and smaller units are defined in relation to the basic meter. for the different units are formed by a prefix The names word to the meter. METRIC MEASURING SYSTEM For motorcycle service, you will measure and centimeters. The millimeter common is symbolized by the lowercase customary system is '/loo Currently, there are two measuring systems in use. In the United States, the English or which began in England has a long history and tradition. ters of a meter and cm. From these is is '/i.ooo letters in millimeters of a meter and mm. The definitions, shown world. Historically, motorcycles manufactured in England mark millimeter. For and the United States use English customary measure- racy, half-millimeter divisions are ments. Those from Europe and Japan use metric measure- the ruler. ments and metric ters only, since that is is the system in use in most of the tools. In order to standardize the measuring systems of all in- As at the top represents Most metric Australia, and other English-speaking countries are switch- mea- suring system will be in use. Until that time, the motorcycle technician must be able to use both measuring systems. METRIC UNITS OF MEASURE In the metric system, as in every system, there are seven common areas of measurement: length, mass, time, elec- MULTIPLE OR in Figure 4-2, 1 each more accushown at the bottom of today are marked in millime- considered to be the standard unit. a motorcycle technician, you will dustrialized countries, the United States, England, Canada, ing to the metric system. Eventually, only the metric rulers 1 let- 10 millimeters equals centimeter. In the steel ruler The metric system centimeter symbolized by the lowercase work in millimeters UNIT 32 >I>|||rmii FASTENERS WITH THREADS ® m BOLT HEXAGON SQUARE TRUSS ROUND OVAL FLAT BOLT PARTS A SET SCREWS / Figure 5-2. A machine screw threads threaded hole. CONE CUP into TRUSS PLAIN OR SLOTTED THUMB FLAT SQUARE ALLEN HEAD HEAD SCREW HEAD Common types of machine FILLISTER PHILLIPS ALLEN THREADED HOLE 49 a Figure 5-3. screw heads. (Ford Motor Co.) FULL DOG FLAT OVAL HANGER HALF DOG SETSCREW POINTS COMMON SQUARE SLOTTED V ALLEN KNURLED WING f HEADLESS THUMB SETSCREW SHAFT Figure 5-4. Top: set screw types. Bottom: cross-sectional view shows how a set screw is used to hold a part to a shaft. (U.S. Navy) Studs Studs are fasteners with threads the stud fits other motorcycle part are at both ends. One end of An- into a threaded hole in a motorcycle part. fits over the stud, and the two parts clamped together with a nut as shown in Figure Studs are often used where the positioning of a part 5-7. is im- portant. Nuts Figure 5-5. Bolts are used with a nut to fas- more parts together. None of the parts have threaded holes. (U.S. Navy) ten two or Nuts are used to secure bolts that go through two or more motorcycle parts, none of which is threaded. Nuts are also used on studs to mount parts or components. The com- monly used nuts are shown in Figure 5-8. The hex nut is UNIT 50 5: Assembling and Fastening Devices "LENGTH NUT DIAMETER STUD THREADED HOLE NUT PARTS Figure 5-7. Studs ends, (U.S. Navy) HEXAGON c^ are HEXAGON WASHER FACED threaded both at SQUARE (CHAMFER) (CMi PLAIN io SQUARE Machine bolts and screws are Figure 5-6. Measuring machine bolts and screws, (U.S. Navy) common most blies. Some HEXAGONAL CASTELLATED JAM measured from end to under head. Slant head bolts and screws are measured to the top of the head. the HEX. CAP WING THUMB CAP Figure 5-8. Motor Co.) Common types of STOP nuts, (Ford type of nut used in motorcycle assem- nuts (and bolt heads) have a flange to increase their bearing surface (Figure 5-8, bottom). If the nut is subject to vibration, as it is in a motorcycle wheel assembly, a castellated nut and cotter pin may be used. After the castellated nut stud, a metal cotter pin is is tightened onto the bolt or inserted through its slots and also through a hole that has been drilled in the stud ter the cotter pin is installed, bent around the nut as shown in it is Figure 5-9. A castellated nut cotter pin, (U.S. is used with a Navy) or bolt. Af- Figure 5-9. The cotter pin prevents the nut from working loose. The washer helps spread out scratched as the bolt head or nut Under severe Washers the clamping force over a wider area and also prevents machined surfaces from being is tightened. vibration, nuts or screws can work them- selves off the bolts or out of their threaded holes. This is prevented by the use of lock washers. Lock washers are Washers (Figure 5-10) are often used with bolts, screws, studs, and nuts. A flat washer is often used between a nut and a motorcycle pan or under the head of a screw or bolt. designed to "bite" into both the nut and the surface the nut bears against. Shakeproof washers do the same and consequently also prevent the nut from loosening. FASTENERS WITH THREADS 3 FLAT WASHER Common Figure 5-10. fL/.S. Navy) MARK AND EMBOSSED AT TOP OF HEAD ]" HEX. BOLT SHAKE PROOF LOCK WASHER SPLIT 51 WASHER SEMI-SPHERICAL EMBOSSMENT types of washers, CROSS SCREW Fastener size and thread types SEMI-SPHERICAL DIMPLE Motorcycles which are manufactured using the metric sys- NUT tem have metric threads. Motorcycles manufactured using the English system use English thread types. The fasteners Figure 5-12. ISO fastener marks, (Honda Motor Co., Ltd.) identification of one system cannot be mixed with those of the other system. Metric system threads Bolts in the metric system have threads cut to millimeter A common metric system bolt might be 1.75 (Figure 5-11). the fas- specifications. M12x tener has metric threads. The M indicates that The first number is either the out- ISO system fasteners are often identified with marks, as shown in Figure 5-12. Be sure you have the correct metric fastener for the job. Do not use JIS wrenches on ISO threads or ISO wrenches on JIS threads: you may damage the threads. English system threads side millimeter diameter of the bolt, screw, or stud or the inside diameter of a nut. Here, number, pitch the distance is in millimeters. it is 12 multiplication sign, after the The mm. The is between each of the threads, larger the pitch second The measured the pitch. number, the wider the under the head the metric bolt or screw to the end and use a thread designation system called the Unified System. The Unified System has two general types of is given is measured from The older system UNF threads, for Unified is tighten a coarse-threaded damage threads will aluminum screw into a hole with parts because they provide greater holding in has been replaced by the newer ISO (International Stand- strength in soft materials. Fine threads are used in ardization Organization) system used in other metric sys- harder materials, such as cast iron and tem countries. The differences thread (Unified National Extra Fine) bolts and ISO bolts are dimensions of JIS in the thread pitch, the width across and the thickness of the head. Because of the second item, metric wrenches are not interchangeable between the the used size of a threaded English nated in the same The many two systems. way DIAMETER (Figure 5-13). 12 mm number of refers to the and the UNF '/2-inch Unified National is not is desig- system fastener. A typical designation represents '/: V2 inch; when threads be designated a is bolt, applied to fits. The threads in every inch of length, denotes Unified National Fine threads. All (20) Coarse thread fastener Figure 5-11. Measurements on a metric system bolt, A hex-head bolt, M 12x1 75 is shown, (Ford Motor Co.) but refers to the size of the bolt that the nut it number of LENGTH M 12x 1.75 made system fastener The screw, or stud thread diameter of 20 many A UNEF different sizes of bolts, screws, studs, and nuts UNF '/2-20 a nut. also as that of a metric are given in fractions of an inch. THREAD PITCH 1.75 (THREADS IN ONE MILLIMETER) is steel. motorcycle manufacture. in The flat, fine the threads. Coarse threads are used termed JIS, for Japanese Industrial Standard. This system in the The for Unified National Fine. coarse thread has fewer threads per inch (larger pitch) than the fine thread and can be easily recognized. Trying to in millimeters. Japanese motorcycles have been manufactured using two different pitch dimension standards. UNC coarse and fine, denoted, respectively, by National Coarse and spacing between the threads. The length of Motorcycles manufactured using the English inch system '/:-13 Fine fasteners have the same per inch. that is UNC. It A Unified V2 inch in National diameter would would have only 13 threads per inch. A distinction to the location letter A to is made between bolts and nuts in regard of their threads. Bolts are designated by the denote that they have external threads; nuts or UNIT 52 5: Assembling and Fastening Devices THREAD PITCH (THREADS IN The strength of a threaded fastener is indicated by a marking system on the screw or bolt head and nut. The marks made are called grade markings. Metric fasteners 20 ONE INCH) use numbers to indicate their strength. The higher the num- DIAMETER 'h INCH ber, the stronger the fastener Grade markings on for English '/j Vz letter B therein. describes a bolt because The 2 preceding the A of the A the quality bolt with A dots, the stronger the nut is. Identifying fasteners contained refers to the class of fit: threads in general use are normally designated by a 2. A UNF-2B describes a nut or threaded B designates internal threads. bolt screw or stud may be given in the The many different types of threaded fasteners used ferent manufacturers' motorcycles make it on dif- difficult for the designation of Vz-lO motorcycle technician to select the correct fastener. hole; again, the letter pitch gauge (Figure 5-16) The length of a designation of a bolt As inch long. in the — for example, '/2-13 UNC-2Axl case of metric bolts, the lengths of fastener threads. blade. on a base of the head. are UNF and UNC bolts and nuts look the same The slight difference however, make them incompatible. as their metric counterparts. and pitch, Most threaded The gauge has a number of blades with The thread size is written on the By matching fastener, made the teeth for both metric shows how the initial selection of fasteners for a given application. the pitch gauge To Taps A inside or internal threads. well as the correct nominal diameter, thread pitch, length, pair screw threads and metals and plastics. 10 used. and screw or bolt extractors. assure continued satisfactory motorcycle performance, re- ARABIC is parts are often damaged by wear or abuse. You will consequently have to be able to use some thread repair tools such as taps, dies, helicoils, placement fasteners should be of the correct strength, as 9 gauges and hardness. These specifications are carefully considered in ARABIC size. Pitch and English threads. Figure 5-17 Threaded fasteners on motorcycle mechani- given in the specifications. on the blade with the threads you can determine thread THREAD REPAIR fasteners are selected according to motorcy- cal properties, such as tensile strength, yield strength, finish, A a useful tool in identifying in size Fastener strength or grade markings cle engineers' specifications that define required is different-sized teeth. English bolts and screws are measured from the end to the Visually, no of the lowest quality. Six marks are is to denote that they have internal threads. Thus, a designation of Vi-lO UNF-2A show motorcycle parts. Nuts have a dot marking system. The more threaded holes are designated by the Figure 5-14. the heads of bolts used for a grade-eight boh, the highest quality bolt used on UNF 20 be. Typical metric in system fasteners (Figure 5-15). marks on the head Figure 5-13. An English-system bolt, {fo!d Motor Co.) Metric bolts are always and strength numbers are shown bolt LENGTH - 20UNF - 2A is. numbered, while nuts may or may not tap (Figure 5-18) is up a cutting tool used to Hand to 25 A make or repair taps are used to cut or re- mm (I inch) in diameter in soft hand tap looks like a fluted screw; Figure 5-14. Metric bolt and nut strength identification numbers. (Ford Motor Co.) THREAD REPAIR 53 GAUGING EXTERNAL THREADS GRADE 5 DOTS 3 GAUGING INTERNAL THREADS Figure 5-17. Using the pitch gauge checking threads. (U.S. Navy) GRADE 6 8 for DOTS Figure 5-15. Grade system for English threaded fasteners. (Ford Motor Co.) TAP WRENCH TAP Figure 5-18. Taps are used to make or pair internal threads. (U.S. Navy) A Figure 5-16. tify it will cut pitch gauge is used re- to iden- threads. its own threads in a hole of the correct diameter. There are many different sizes of taps. The size is indi- cated by numbers on the shank of the tap which show the diameter and pitch of the thread the tap will cut. To repair an internal thread, select a tap with the same diameter and thread pitch as the damaged thread. Then clamp Now end of the tap shank the square in a tap wrench. place the tapered end of the tap in the hole, so that the tap is in line with the hole (Figure 5-19). Start the tap- ping by turning the wrench about a quarter of a turn Figure 5-19. Using the tap bored hole. (U.S. Navy) clockwise for a right-hand thread and counterclockwise for a left-hand thread. Then back the tap off about a third of a turn. Now back off a quarter of a turn. This procedure provides a it turn the tap forward about half a turn, and skill and practice. The rod correct diameter. If is to be threaded the proper dimension, the end Some Dies nal threads. A die is is held in a handle called a die stock. easier than tapping, but it still requires is of to thread on the rod. dies are adjustable so that correct, slightly over- and slightly undersized threads can be justment is done by means of Once made, it will stay that sized, Cutting with dies you are going should be tapered, but only slightly. This allows the die to get a start Dies (Figure 5-20) are used for cutting or repairing exter- in the must be of the tapped hole. Assuming that the rod a sloppy from the metal to be removed from the bottom of the which does the actual cutting. fit a thread a little undersized, the resuh will be firm grip for the tap and allows the metal chips that are cut tap, to is When you way a screw. until it is cut. The ad- the adjustment purposely changed. are ready to start cutting a thread, mount the UNIT 54 Assembling and Fastening Devices 5: y&s-^ DIE Figure 5-20. A die in a die stocl< is used to cut or repair external threads. (U.S. Navy) The required die in a die stock of the correct size. marked on sizes are Figure 5-21. Using the die to cut threads on a rod or re-form damaged bolt threads. (U.S. Navy) and the die and correspond to the diameter thread pitch of the thread to be cut. When you look you at the die, ing at the center of one face opening is The at the The other side. one with which you the die-cutting procedure Be dure. will notice that the open- just slightly larger than the is larger of the start the is two openings threading operation. similar to the tapping proce- sure the rod to be threaded a right angle to is at the die. Start the die squarely over the rod, give turn forward and back it a quarter off about one-eighth of a turn. it Keep on turning and backing off, a little at a time, until you have cut the amount of thread you need (Figure 5-21). Dies are sometimes used to repair threads on a damaged bolt. Screw thread If inserts (helicoiis®) an internal thread too badly damaged, is can be it A paired with a screw thread insert (Figure 5-22). thread insert or helicoil® wound into the hole to coil® tap The is A is is special heli- used to prepare the hole for the thread helicoil® sert tool which a steel wire coil is form a new thread. re- screw insert. then threaded into place with a special in- (Figure 5-23). The machine screw or then be installed by using the helicoil® for new bolt can threads. Screw and stud extractors Broken screws, studs, motorcycle repair. If a and bolts are surface, you can usually grip screw (Figure 5-24). If it surface, it will be common problems it it it much more difficult to remove. If is If hammer you can to turn the bolt or stud. no part remains above the surface, or insert or helicoil. (Heli-Coil) only by using a punch (Figure 5-25). Hit the punch with a ball pein 5-22. Badly Figure damaged internal threads can be replaced by a screw thread with locking pliers and un- breaks off flush or below the a small stub remains above the surface, sometimes turn in screw or stud breaks off above the hole in the exact center of the broken fastener (Figure 5-26). drill. if the fastener frozen in the hole, you must begin by drilling a small You If then enlarge the hole by using a slightly larger necessary, do stud or screw is left. it again, until only a thin shell of Finally, force an extractor (Figure THREAD REPAIR 55 BorTlled »^^' HOLE ^ t INSERTING TOOL EXTRACTOR Figure 5-23. Screw thread insert tools. Figure 5-26. Navy) Drill out the broken fastener. (U.S. Figure 5-24. Using locking pliers screw a broi^en bolt. (U.S. Navy) to un- 11^ A bolt or screw extractor remove broken bolts, studs, Figure 5-27. used to is or screws. Different-size extractors are available. (U.S. Navy) TURN COUNTERCLOCK WISE EXTRACTOR Figure 5-25. Using a punch and hammer to unscrew a broi threaded hole. Nut: a small fastener with internal threads used with bolts and studs. Pitch gauge: a tool used to measure the thread size of a threaded fastener or hole. Identify each of the measurements on the fastener shown below. Set screw: machine screw that threads through one part to hold it 11. to another part. Sruip ring: an internal or external ring used to hold motor- cycle components together. 12. 13. Splines: teeth cut into a shaft or gear so that they will fit and hold together. 11 Stud: a fastener with threads at B^«^ both ends. Tap: tool used to cut threads in a hole. Washer: a fastener used with bolts, screws, to distribute the clamping force in order teners from coming loose due studs, and nuts to prevent fas- 13 to vibrations. 12 CHECKUP Identify the thread-repair tools Identify the types of screws trations shown in each of the shown below. illus- 14. below. 15. C 14 1 Identify the types of nuts shown in each of the illustrations 15 below. 4. DISCUSSION TOPICS AND ACTIVITIES 5. 1. 6. Make a list of all the types of fasteners you can find on a shop motorcycle. 2. 6 Measure a collection of shop fasteners and see if you can tell the difference between metric and English threads. Use a pitch gauge to check your results. I he motorcycle engine machine a is that converts heat energy into a form of power. All motorcycle engines oper- on the basic principle of combustion: when fuel is mixed with air and burned, heat is produced. This heat de- ate velops useful power. In this unit, we look at the basic parts of the two- and four-stroke motorcycle engine and work together they to how develop power. JOB COMPETENCY OBJECTIVES When you be able and studying finish reading this unit, you should to: Identify the basic parts and describe the operation of 1. an internal combustion engine. ENGINE FUNDAMENTALS Describe the parts and operation of a two-stroke cycle 2. engine. Explain the operation and identify the parts of a four- 3. stroke cycle engine. Define the terms used to describe an engine's size and 4. COMBUSTION CHAMBER performance. BASIC ENGINE PARTS AND OPERATION On motorcycle engines, combustion takes place inside all the engine. This ternal is is why motorcycle engines are called combustion engines. An internal combustion engine which we put really just a container into PISTON in- air and fuel and then start them burning. The container used gine is the cylinder, for burning the air which one end. The plug that There is fits and fuel in an en- simply a metal tube closed is inside the cylinder is INTERNAL COMBUSTION ENGINE at Figure a piston. tfie 6-2. Combustion down piston pressures force the cylinder. (U.S. Navy) a small space between the piston and the top of where the burning takes place. This space is known as the combustion chamber. The basic parts required for internal combustion are shown in Figure 6-1. Let's put several drops of gasoline into the space above the cylinder the piston. As we move gasoline-air mixture pressed. When the piston in the the mixture up it, force, as When compressed as tightly as we start it burning with an electric spark. This ber and pushes the piston com- is we combustion increases the pressure in the cylinder, the combustion chamber is can get shown down in the combustion cham- the cylinder with great in Figure 6-2. the piston moves down duced. Our problem is end, a connecting rod the cylinder, to harness that is power is pro- power. Toward that connected to the bottom of the is forced downward, the rod moves downward. This downward movement is changed to circular movement at the crankshaft, which is a shaft with its middle offset and its ends mounted so that it can piston, COMBUSTION CHAMBER and as the piston turn freely. Since the lower end of the connecting rod CYLINDER- is connected to the crankshaft and the upper end is connected to the piston (through a piston pin), the connecting rod can PISTON follow the crankshaft's motion. The parts that connect the piston to the crankshaft are shown in Figure 6-3. If down have more than one piston movement the cylinder, we have to bring the piston back up the we want cylinder. Thus, Figure 6-1. Basic parts bustion. (U.S. Navy) for internal com- flywheel. the end to we need one more The flywheel is basic part, called the a heavy wheel of the crankshaft, as shown in that is mounted on Figure 6-^. 61 UNIT 62 6: Engine Fundamentals CYLINDER COMBUSTION CHAMBER PISTON PISTON PIN CONNECTING ROD CONNECTING ROD CRANKSHAFT CRANKSHAFT CUTAWAY VIEW OF PISTON Figure 6-3. The piston is connected nected to a crankshaft. (U.S. Navy) to a connecting rod which in turn, is, con- TOP DEAD CENTER CYLINDER BOTTOM DEAD CENTER Figure 6-5. Piston movement from BDC Figure 6-4. The flywheel keeps the crank- or moves from the piston the flywheel does not slow is forced down, both the crankshaft and go around. Since the flywheel down easily. The momentum of is heavy, the to TDC is it moving BDC back to TDC, another stroke has oc- A series of strokes cycle engine. is Engines used to develop power that causes the piston to go back up to the top of the cylinder. series of events that movement cylinder, called in a cylinder When is very important to en- moves from the top of the top dead center (TDC), to the bottom of the piston that is in a develop their power strokes are called two-stroke cycle engines. Piston to curred. flywheel thus keeps the crankshaft turning, which in turn gine operation. TDC a stroke. the cylinder, called bottom dead center (BDC), we say that one stroke has occurred (Figure 6-5). When the piston shaft turning. As BDC motorin (A cycle two is a repeated over and over.) Engines develop their power four-stroke cycle engines. in four piston strokes are called The next two sections deal with the operation of two- and four-stroke engines. TWO-STROKE CYCLE ENGINE OPERATION 63 — movements or strokes one movement up and one movement down to complete the cycle. — Two-Stroke: basic parts Regardless of whether a motorcycle engine four-stroke cycle engine, it is a two- or has the same two main sections (Figure 6-7): upper end (cylinder) and lower end (crankcase). The upper end houses the piston, the cylinder, and the top of the cylinder, called the cylinder head. The lower end supports the crankshaft. Since the engine is used to drive the rear wheel of the motorcycle, a clutch and transmission are necessary. The parts of the transmission and Figure 6-6. This competition dirt bike is with a two-stroke cycle engine. (U.S. Suzuki Motor Corp.) clutch equipped into the lower end housing. The two-stroke cycle engine uses the same basic parts described previously. As shown Figure 6-8, there in cylinder and a combustion chamber. TWO-STROKE CYCLE ENGINE OPERATION Many fit der is A is a piston in the cylin- connected to a crankshaft by a connecting rod. A is mounted to or combined with the crankshaft. flywheel types of motorcycle are equipped with engines that operate on the two-stroke cycle principle. These engines are often called m'o-cycle engines or two-strokers. Many small street motorcycles and most off-road motorcycles There are two holes or ports in the cylinder: the exhaust burned air-fuel mixture out, and the intake the fresh air and fuel in. A transfer passage port, to let the port, to let connects the crankcase section to the cylinder section. The principle of two complete piston (Figure 6-6) use two-stroke cycle engines. the two-stroke engine is that takes it SPARK PLUG UPPER END EXHAUST PORT CONNECTING ROD LOWER END (CRANKCASE) CRANKSHAFT TRANSMISSION Figure 6-7. Three a motorcycle Corp.) mam engine. engine sections of Suzuki Motor (U.S. Figure 6-8. Basic parts cle engine. (U.S. Suzuki of a two-stroke cy- Motor Corp.) UNIT 64 Engine Fundamentals 6: SPARKPLUG IGNITES SPARKPLUG AND FUEL AIR AIR/FUEL MIXTURE MIXTURE BEING COMPRESSED PISTON MOVING UP EXHAUST GAS EXITS WHEN PISTON ENTERS CRANKCASE AIR/FUEL UNCOVERS THE EXHAUST PORT /o_ MIXTURE VACUUM IN CHAMBER COMPRESSION AND CRANKCASE INTAKE POWER AND CRANKCASE TRANSFER AND EXHAUST COMPRESSION Figure 6-9. Two-stroke cycle. Compression and crankcase intake phase (left). Power and crankcase compression phase (center). Transfer and exhaust phase (right). (U.S. Two-Stroke: how Suzuki Motor Corp.) works it cape out of the crankcase anywhere except through the transfer passage, so Compression and Crankshaft Intake Phase When the piston moves up in the cylinder, the vacuum the piston gets bigger, resulting in a case. An air-fuel mixture same at the is crank- pulled into the crankcase, and, time, the piston covers the intake and exhaust and fuel above the piston are thus trapped. The piston then compresses the mixture in the combustion ports. Air chamber. Figure 6-9 shows (left) this moves down far As the piston moves down, it of this port as soon as it is uncovered. The piston then un- covers the transfer passage, and a fresh charge of fuel enters shows the combustion chamber. Figure 6-9 this transfer Note upward stroke, we is introduce The burning causes piston down, thereby and (right) and exhaust phase. On On one stroke the second stroke it pushed down the cylinder. The crankshaft turns one complete turn or revolution (360 degrees) during these two The two a spark to start the mixture burning. strokes. the expanding gases to force the engine develops power. power to the crankshaft. moves down, the crankcase area becomes smaller and the air-fuel mixture in the crankcase is compressed. The mixture would escape, except that the piston has covered over the intake port. So the mixture is compressed more and more tightly in the crankcase. Figure 69 (center) shows this power and crankcase compression air that while there are several phases of two-stroke the piston compresses the mixture. Power and Crankcase Compression Phase its to un- uncovers the exhaust port. cycle operation, there are only two strokes. the piston approaches enough Since the burned gases are under pressure, they flow out compression and crankcase intake phase. As goes up the transfer passage and cover the passage. space below in the it stands by until the piston strokes are repeated over and over as the transferring the piston's As the piston phase. Transfer As and Exhaust Phase the piston moves down ture in the crankcase makes is As we have seen, intake the air and fuel gases flow through ports. Different engines use different methods of The three main types of system are called piston port, rotary valve, and reed valve systems. controlling the flow of gases through these ports. Piston Port the cylinder, the air-fuel mix- compressed because the piston the crankcase area smaller. Two-Stroke: port control The mixture cannot es- The piston port system to control air is the most common method used and fuel flow. This system was described the discussion of two-stroke cycle operation. in The lower TWO-STROKE CYCLE ENGINE OPERATION 65 AUXILIARY TRANSFER PORT MAIN TRANSFER PORT PORT CLOSING PORT OPENING LOOPS INTAKE PORT AUXILIARY TRANSFER PORT MAIN TRANSFER PORT LOOP ROTARY VALVE MAIN TRANSFER PORT AUXILIARY TRANSFER PORT ^CRANKSHAFT INTAKE PORT (OPEN) DISC Figure 6-11. Operation of a rotary valve control an intake port. of the crankshaft revolution vacuum of fuel to enter the it is to open, allowing the crankcase. As air and the crank- shaft rotates further, the larger part of the valve covers over the port and seals the crankcase (Figure 6-11). INTAKE PORT Reed Valve Another method used valve arrangement. that works plate, as to control the intake port is a reed reed valve is a thin piece of metal like a hinge. Usually, several small reed valves are used together Figure 6-10. Loop scavenging on a piston port engine. (Yamaha Motor Corp. U.S.A.) A shown in and mounted on a plate called the reed Figure 6-12. A leaf-type spring is used to hold the valve in the closed position. edge of the piston used to open and close the intake port is and transfer passage. Most piston port systems arrangement that is make use of a cylinder porting designed to get the exhaust gases out completely without contaminating the incoming fuel charge. Such a technique is In a loop scavenging system, a series of fer ports are located air and called loop scavenging. main and trans- around the cylinder. The main and on opposite sides are used to transtwo streams of air and fuel into the cylinder. The two main streams of fresh fuel meet at the cylinder wall opposite the exhaust ports and deflect upward. Then the streams auxiliary transfer ports fer deflect downward, forcing out exhaust ports. As shown in the burnt gases through the Figure 6-10, the streams create a loop as they flow through the cylinder. Rotary Valve Some engines use a rotary valve instead of the piston to control the flow of air and fuel into the crankcase. valve is an irregular-shaped disc that crankshaft. The shape of the valve is is A rotary mounted to the such that during part REED PLATE Figure 6-12. A reed plate with eight reed valves. (U.S. Suzuki Motor Corp.) UNIT 66 6: Engine Fundamentals Figure 6-14. Large street motorcycles are equipped with a four-stroke cycle engine. (Harley-Davidson Motors, Inc.) often Figure 6-13. An open reed valve allows air fuel to pass through holes in the piston to the crankcase. (U.S. Suzuki Motor Corp.) and When there is a vacuum in the crankcase, the reed valves hinge open because of the low pressure on the crankcase side. The air-fuel mixture through the open valve, and holes is then pulled in in the side of the piston allow the mixture to flow through the piston and into the shown moves down, pressure crankcase, as in Figure 6-13. up starts to build When the piston in the crankcase. This pressure pushes the hinged reed valve closed, and the mixture is trapped in the crankcase. The main advantage of a two-stroke cycle engine is its The two-stroker requires fewer parts to develop power than the four-stroker; it can therefore be lighter than the four-stroke engine. The two-stroke engine works best at high rpms and with unrestricted or unmuffled exhaust. The firing impulse of every crankshaft revolution results in simplicity. the characteristic high-pitched buzzing noise two-stroke engines make. These characteristics make it a natural for off-road riding and competitions. has power in four piston strokes. These engines are sometimes called four-strokers or four-cycle engines. Four complete up and down, are required complete the cycle. Most of the larger street transfer ports, intake ports, and exhaust ports lo- above the piston head (Figure 6-16). ports located its One motorcycle engines use an engine that develops strokes, its of the ports is called the intake port. Many movements or having cated in the cylinder and crankcase, the four-stroke engine the cylinder FOUR-STROKE CYCLE ENGINE OPERATION piston Figure 6-15. This small four-wheel quad runner has a four-stroke cycle engine. (U.S. SuzuiKi Motor Corp.) to motorcycles used to let The other in a air component called and fuel and in port, called the is exhaust port, provides a passage for getting rid of the exhaust gases left after is combustion. Opening and closing the ports accomplished with valves. In most engines, there are two valves above each piston (Figure 6-17). and fuel is The valve used to control the inlet of air referred to as the intake valve. The other, use four-stroke cycle engines (Figure 6-14), but the engine known as the exhaust valve, controls the escape of burned can also be used on small off-road machines (Figure 6-15). gases. The valves have a face, which matches a carefully ground seat in the head. A strong spring called the valve spring holds the valve on its Four-Stroke: basic parts seat for an airtight seal. The valves The four-stroke cycle engine has the carefully ground taper called a same basic parts as the two-stroke engine: a cylinder, piston, piston pin, con- necting rod, crankshaft, and flywheel. However, instead of are opened by a camshaft and rocker arm sembly. The camshaft (Figure 6-18) is as- a shaft driven by which it is connected by a chain. Figure 6-16 shows the camshaft and chain. The camshaft has ec- the crankshaft, to FOUR-STROKE CYCLE ENGINE OPERATION CAMSHAFT 67 ROCKER SHAFTS ROCKER ARM INTAKE VALVE INTAKE PORT VALVE SPRING PISTON CONNECTING ROD VALVE FACE VALVES Figure 6-17. Two valves are located above thie piston to control ports. intake tfie (Yamaha Motor Corp. and exfiaust U.S.A.) ROCKER ARM ROCKER SHAFT CRANKSHAFT CAMSHAFT Figure 6-16. Basic parts of a four-stroke cycle engine. (Honda Motor Corp., Ltd.) Gentries or lobes, one for each intake valve and VALVE SPRING one for A rocker arm is mounted on a rocker above the camshaft. Figure 6-17 shows the rocker each exhaust valve. shaft arms and VALVE SEAT Figure 6-18. Thie camshiaft and rocker arms the valves. (Yamaha Motor Corp. shafts. The rocker arm is essentially a lever with its on the camshaft lobe. As the high part of resting shaft lobe rotates under the free arm moves up. by the rocker The center of shaft, which end cam- free the end of the rocker arm, the the rocker arm is open supported acts like a fulcrum or lever As the free end moves up, the other end of the rocker arm moves down, pushing on the end of the valve and thereby causing it to move off its seat and open the point. port. Further rotation of the camshaft allows the low side of cam to contact the rocker arm end, so that the arm is no longer being pushed down. The valve spring, which the was compressed when the valve opened, closes the valve and pushes the end of the rocker arm (over the valve) back up. U.S.A.) intake and the exhaust valves closed; the piston in the cylinder as the crankshaft permit it is as far up and connecting rod will to go. Intake Stroke The intake stroke (Figure 6-19, left, number 1) begins when the piston begins to move down the cylinder. This rapid movement of the piston creates a low-pressure area above the piston. If we open the intake valve piston, a mixture of air and fuel filling it. The piston has is above the forced into the cylinder, now completed one stroke from the top to the bottom of the cylinder, and the crankshaft has turned one-half turn, or 180 degrees. Four-Stroke: We are now how it works Compression Stroke ready to describe the action that occurs during one complete cycle of operation. We start with both the As the piston starts up for the compression stroke, the take and exhaust valves are closed. The piston travels in- up UNIT 68 6: Engine Fundamentals 3 1 COMPRESSION: AIR/FUEL MIXTURE INTAKE IS COMPRESSED Figure 6-19. Four-stroke cycle. air and (1) Intake stroke: piston fuel to enter the cylinder thirough the stroke: the piston mixture. (3) Power 4 EXHAUST POWER moves up open moves down, causing Compression compress the air-fuel intake valve. (2) with both valves closed to stroke: a spark from the spark plug ignites the air-fuel mix- ture, forcing the piston down the cylinder. (4) Exhaust stroke: the piston moves of the open exhaust valve. (Kawasaki Motors back up, forcing burned gases out Corp. U.S.A.) as far as it can go, compressing the air-fuel mixture combustion chamber former volume (Figure 6-19, number air are in the into a space about one-eighth of thus forced lightly together. its The molecules of The crankshaft has 2). turned another 180 degrees, completing one revolution. During this phase, the intake and exhaust valves remain closed. Exhaust Stroke The exhaust stroke (Figure 6-19, right, as the piston again starts to number move upward This time, however, the exhaust valve is 4) begins in the cylinder. opened. Burned gases trapped in the cylinder are pushed out the exhaust port as the piston moves upward. The piston completes an- other stroke from the bottom of the cylinder to the top, while the crankshaft has turned another one-half turn or 180 degrees. In Power Stroke As its topmost point on the compression from an ignition system is used to ignite the piston nears stroke, a spark the air-fuel mixture. causing a rapid rise Once ignited, the fuel bums down the cylinder When the piston reaches the • on the power stroke is over. bottom of the cylinder, the The crankshaft turns another 1 remain closed. The power stroke 3). is shown in and fuel trapped Power: air-fuel 80 de- Figure 6-19 the top of the cylinder and fuel are pulled in through an Compression: The piston moves up, compressing the air • A in the cylinder. spark from the ignition system ignites the mixture, causing a rise in pressure which pushes the piston down. grees during this stroke, and the exhaust and intake valves (number The piston moves from open intake valve. stroke and causes the crankshaft to rotate. power Intake: the four strokes of the engine are: to the bottom; air quickly, pressure in the cylinder. This rise in in turn forces the piston • summary, • Exhaust: The piston moves up, pushing burned gases out of the cylinder through an open exhaust port. ENGINE SIZE AND PERFORMANCE MEASUREMENTS These four strokes make up one complete cycle which is 69 CAMSHAFT SPROCKET repeated over and over to develop power. Each cycle re- quires four strokes of the piston and two revolutions of the - crankshaft. CAM CHAIN Valve Operation The operation of Intake: • The the valves in the four-stroke cycle intake valve CAMSHAFT is: pushed open by the cam- is shaft. Compression: Both valves are held closed by the valve • springs. Power: Both valves remain closed, held by the valve • springs. Exhaust: The camshaft pushes the exhaust valve open. • The valves must open at just the right time in the four- stroke cycle. In order to time the valve openings so that they coincide with the piston strokes, the camshaft is driven by gears or a chain directly from the crankshaft. Since a valve must be open only during two strokes, intake and exhaust, the camshaft needs the crankshaft speed. to rotate at only one-half The gear or sprocket on the camshaft thus twice as large as that on the crankshaft. Timing is marks on the two gears or sprockets are used the camshaft A cam and crankshaft are to make sure in the correct relationship. chain and sprocket assembly are shown in Figure 6-20. It Figure 6-20. The camshaft is driven at half crankshaft speed by a sprocket and chain assembly. (Yamaha Motor Corp. U.S.A.) should be obvious that the four-stroke engine has more parts and ever, a is heavier than the two-stroker. number of characteristics choice for a street motorcycle: (1) a two-stroke engine. (2) much longer. (3) It stroke engine. (4) It It which make It is can run much at a howa good has, it quieter than lower speed for uses less fuel than the same size two- It can be made to develop a great deal MEASUREMENTS Many and arrangements of these in a later unit. Motorcycle engines are characterized by a number of measurements and performance measurements, among which are bore, stroke displacement, torque, and horsepower. ENGINE SIZE AND PERFORMANCE inder. shall describe the designs size of smooth, quiet power. The engines so We engines Bore and stroke far described have a single piston and cyl- motorcycles have a single-cylinder engine. Other motorcycles have engines with two (twin), three, or four cylinders. These multiple-cylinder engines may oper- on either the four- or two-stroke principle. When the engine has more than one cylinder, the crank- ate The bore of an engine its powerful the engine ton is a cylinder (Figure 6-21). moves from from the top the to the is. measurement of the diameter of The larger the bore, the more The stroke are occurring in each cylinder. In a four-cylinder engine, may be moving down on intake, compression, another down on power, and another up on powerful the engine another up on millimeters, with the bore written A power stroke is much more smoothly and can shaft. These engines operate develop much more power than a single-cylinder engine. is the distance between and the centerline of the connecting rod where mined by taches to the crankshaft. exhaust. to the top, or is. mensions are always given is it at- The longer the stroke, the more The bore and stroke are given in first. and stroke specifications may be 57 where the motorcycle deter- the centerline of the crank- shaft always pushing on the crank- the distance the pis- bottom. The size of the stroke shaft is designed so that at a given time different strokes one piston is bottom of the cylinder in For example, bore mm x 48.8 mm. Di- millimeters, regardless of manufactured. 70 UNIT 6: Engine Fundamentals where it and stroke specification STROKE DISPLACEMENT (VOLUME) R has the value 3.14, diameter) of the bore, and 5 is Displacement To change 124,462 is is the radius (one-half the the stroke. Thus, if the bore mm x 48.8 mm. 57 = tjR'S = 3.14X28.50-X48.8 = 3.14x812.25x48.8 "= 124,462 mm mm to centimers, divide divide by 100 to get cubic centimeters (cc). 124.462 124.462 cc. cc. Our engine has thus by The 10; then result is displacement a of Motorcycle manufacturers, however, use the next whole number, so this engine is described as a 125- cc engine. Figure 6-21. Engines bore and stroke. described are Displacement by is motorcycle engine. their cc, the most common way Common of describing a engine displacements are 50 80 cc, 125 cc, 250 cc, 500 cc, 550 cc, 750 cc, 1,000 cc and 1,150 cc. Figure 6-23 shows a three-wheeler with Displacement a displacement of 125 cc; Figure volume the pistons displace during one stroke (Figure 6-22). The bigger the displacement, the more air and fuel that are brought in on the intake stroke and the more the power that is de- The displacement of an engine is the area or 6-24 shows a wheeler with a displacement of 1,150 cc. large two- Remember, veloped. The bore and stroke of an engine are used to find its displacement. Displacement measured is starting with The bigger the larger the volume or the piston at the bottom of the cylinder. bore and the longer the stroke, the displacement. If the engine has more than one cylinder, the displacements of all the cylinders are added together to de- termine the total displacement for the engine. The volume or displacement of a cylinder can be deter- mined by the formula Displacement = itR^S AREA Figure 6-23. This small three-wheeler has an engine with a displacement of 125 cc. (US Suzuki Motor Corp.) STROKE VOLUME Figure 6-22. Displacement volume of the cylinder. is the area or Figure 6-24. This large street motorcycle has a displacement of 1 150 cc. (U.S. Suzuki Motor Corp.) if an ENGINE SIZE AND PERFORMANCE MEASUREMENTS 100 CUBIC INCHES H PISTON AT BDC PISTON AT TDC Figure 6-25. A compression ratio of we have engine has more than one cylinder, 1 to 1 to multiply the displacement of one cylinder by the number of cylinders to get the total engine displacement. Compression The compression ratio measurement that indicates how is compressed on the compresdefined as the ratio of the volume of the ratio is a tightly the air-fuel mixture sion stroke. It is when cylinder the piston is at bottom of the volume of the clearance volume, i.e., the above the piston when the piston is at stroke to its the small area the top of stroke. its For example, suppose the volume of the cylinder cubic inches der. when Suppose also the cylinder, the piston that when is at is 100 the bottom of the cylin- the piston goes to the top of the air-fuel mixture is compressed into a clearance volume of only 10 cubic inches. (See Figure 625). Then ratios for 10 to the compression ratio is 10 to 1. Compression most current motorcycles are between 8 to 1 and 1. Horsepower and torque may be characterized by the amount of horsepower and torque they develop. Power is the rate or Motorcycle engines speed of doing some work. The type of power describe an engine is we use to horsepower. The unit of horsepower was developed a long time ago when man wanted to compare the work performed by steam engines to the work a horse could do. The horsepower of an engine can be determined mathematically by measuring the engine's torque at any particular rpm Torque (revolutions per minute) of the engine crankshaft. is which measures turning or mechanic using a wrench to tighten a a rotary unit of force twisting effort. A bolt applies torque to the bolt. that it no longer turns, the apply torque. Thus, torque to produce rotation. When the bolt mechanic may is still is so tight be able to a force that produces or tends 90 71 UNIT 72 the test is 6: Engine Fundamentals complete, all the marks are connected together form a curve. The horsepower curve in Figure 6-26 is common to most engines. Horsepower does not start at zero because to an engine will not run is zero speed. Therefore, the curve at Horsepower increases cut off at the bottom. as the en- gine speed and load increase. According to the graph, the engine shown in BHP at it reaches An 5,000 rpm. horsepower begins its maximum horsepower engine can run faster than to decrease after reaching the of 72 but this, maximum point. The torque curve shows engine at different speeds the load-carrying ability of the in pound-feet or newton meters. The relationship between the torque curve and the horsepower curve shows how the engine will perform at differThe horsepower curve continues to ent loads and speeds. climb as the engine speed increases, power is reached. This Figure 6-26 in maximum horse- also true of the torque curve, but is the torque curve will reach Notice until how much highest point its earlier. the torque curve drops after it its peak point (maximum) at 4,000 rpm. The torque of most engines varies widely over the normal range of crankshaft speeds. At very low speeds 200 to 300 rpm an engine develops only enough torque to reaches — — keep itself running. At these speeds, practically zero. increases to a peak. This is horsepower its As engine speed and load dis- placement. Brake horsepower: horsepower measured flywheel; abbreviated Combustion chamber: at the engine's BHP. part of the engine in which the burn- ing of air and fuel takes place. Compression the ratio: amount the compressed during the compression air-fuel mixture is stroke. Compression stroke: that stroke of a four-stroke cycle engine during which the air is compressed. Connecting rod: an engine part that connects the piston to the crankshaft. Crankshaft: an offset shaft to which the pistons and connecting rods are attached. Cylinder: a tube in which an engine's piston moves. Displacement: the cylinder volume displaced by the pistons of an engine. Engine: a machine that converts heat into a usable form of energy. Exhaust stroke: that stroke of a four-stroke cycle engine during which the exhaust gases are pushed out. is increase, torque where the manufacturer Bottom dead center (BDC): highest power of piston rates the torque, very near the most efficient operating speed of the engine. At this point, the cylinder or cylinders are tak- ing in the biggest and most efficient air-fuel mixture, and the exhaust gases in the cylinder are being forced out most Four-stroke cycle engine: an engine that develops power through four strokes of a piston. Flywheel: a heavy wheel used to smooth out the power strokes. Horsepower: a unit of power used developed by an engine. to describe the power effectively. The torque curve drops higher engine rpm, there to enter, off rapidly after its peak. At is less time for the air-fuel charge and the exhaust gases to leave, the cylinder. This causes a weaker push on the pistons and consequently, less torque. Other factors which contribute to the drop in torque pumping losses. Power is is pumping in air and fuel, are internal engine friction and wasted in an engine when and then exhausting it. The horsepower curve curve, since torque for horsepower. it is is directly affected one of the elements However, the by the torque in the horsepower curve does not directly correspond to the torque curve because affected by another element, time. Recall that speed or rate is at which work is formula it is power also is the done. The horsepower curve able to increase past the peak of the torque curve be- cause the engine rpm increases beyond this point. Eventually, however, the torque drops off so much more rpm cannot hold the that even horsepower curve up. KEY TERMS Bore: a measurement taken across the diameter of a cylinder. Intake stroke: that stroke of a four-stroke cycle engine during which air and fuel enter the engine. Internal combustion engine: an engine in which the burning of fuel takes place inside the engine. Piston: cylindrical metal part attached to the connecting rod; the piston slides Power up and down in the cylinder. stroke: that stroke of a four-stroke cycle engine dur- power ing which Stroke: the stroke is is delivered to the crankshaft. movement of the piston in the cylinder; the controlled and measured by the offset of the crankshaft. Top dead center (TDC); lowest point of piston displace- ment. Torque: a turning or twisting effort or force. Two-stroke cycle engine: an engine that develops power in two piston strokes. CHECKUP Identify the basic parts of an engine in the spaces provided. by writing their names DISCUSSION TOPICS AND ACTIVITIES 1. 73 Describe the operation of each of the two-stroke phases shown below. 2. 3. 12. 4. 5. 13. 6. 7. 14. 4 -31 Identify the parts of a four-stroke cycle engine in the spaces provided. 15. 16. Identify the parts of a two-stroke engine in the spaces pro- 17. vided. 18. 19. 9. 10. 11. 74 UNIT 6: Engine Fundamentals Explain the operation of each of the strokes of the fourstroke cycle engine 23. shown below. DISCUSSION TOPICS AND ACTIVITIES 20. 1. Remove gine. 21. a cylinder head from a two-stroke cycle en- Turn the engine over and identify each phase of operation. 2. Remove gine. 22. the valve cover opening and closing. strokes. 20 21 22 from a four-stroke cycle en- Turn the engine over and observe the valves 23 Identify each of the four iTAs a motorcycle technician, you will be called perform many engine servicing jobs. understand structed. how You an engine works, but also Engine construction is As make an engine how it is concerned with the ent types and designs of engine parts and gether to upon to not only need to how con- differ- they fit to- (Figure 7-1). detailed in the last unit, a motorcycle engine can be divided into two basic areas: the upper end and the lower The upper end end. consists of the cylinder, piston, and cylinder head. If the engine runs on a four-stroke cycle, the upper-end cylinder head includes the valves and the valve operating mechanism. The lower end includes the crankcase, the crankshaft, and the connecting rod. The two ends are designed so that the upper end can be separated from the lower end the common parts for servicing. In this unit, and arrangements used four-stroke cycle upper ends. The next in we describe both two- and unit discusses lower UPPER-END PARTS AND CONSTRUCTION ends. JOB COMPETENCY OBJECTIVES When you be able finish reading this unit, you should to: common types of cylinder design and at- tachments. Identify the different types of pistons used in two- and 2. fitted four-stroke engines. Identify the is cast a tight bond, and the liner pro- an excellent conductor which removes heat from the cylinder. Some to the engines use a thin layer of chrome applied directly aluminum cylinder. Chrome plating provides a very The cylinder must be held tightly to the crankcase be- cause the forces of combustion tend to pull major parts of a two- and four-stroke cyl- Identify the parts of a valve operating A common case. crankcase inder head. 5. make hard, long- wearing surface for the piston to ride on. the oil-control piston rings. 4. liner to num makes Explain the purpose and operation of compression and 3. with a cast iron liner or sleeve. The aluminum around the vides a cast iron surface for the piston to ride on. Alumi- Describe the 1 and studying cylinder mechanism. it off the crank- retaining the cylinder to the to thread long studs into the crankcase. is fits method of The over the studs, and the cylinder head and a nut hold the assembly together (Figure 7-3). Usually four studs are used on each cylinder. CYLINDERS Another common method is to form a flange around the bottom of the cylinder and use short studs or hex-head The cylinder (sometimes opening in called the barrel) provides the which the piston made from an aluminum slides up and down and or iron casting (Figure 7-2). is The cylinder walls are machined to very close tolerances. If the engine is of the single-cylinder variety, there is one indi- vidual cylinder. If the engine has two or more cylinders, both may be cast together in the twin cylinders If the engine shown is in one part, as is will have passages around the cylinder for coolant circula- The case, and four best surface for the sliding piston is cast iron. is that it is shows how four short studs more studs to fasten the head to the cyl- The barrel or cylinder used on a two-stroke cycle engine made from the same material and is held in the same position as those described for the four-stroke cycle en- The main difference is that the two-stroke barrel must have transfer and exhaust ports cast into it, as shown gine. Figure 7-5. Many engines use a cast iron cylinder assembly. The problem with cast iron, however, 7^ inder. in tion. The held in position with another set of studs is or hex-head bolts. Figure is around the cylinder to remove heat. Liquid-cooled engines to fasten the cylinder flange to the crankcase. with hex nuts are used to fasten the cylinder to the crank- the case with Figure 7-2. cooled, cooling fins will be cast air bohs cylinder head very heavy. Hence, PISTONS in produced by burn- The piston's job inder assembly from aluminum. Since ing fuel for the actual cylinder walls, through the connecting rod. The piston must be as light as order to reduce weight, it is necessary to cast the basic cyl- aluminum is too soft most aluminum cylinders are in the is to transmit the force combustion chamber to the crankshaft 75 76 UNIT 7: Upper-End Parts and Construction Figure 7-1. Engine construction is concerned with how the parts engine. (Honda Motor Co. Ltd.) fit together to make an possible, but strong exerted on enough to withstand the great forces Pistons are cast or forged from makes them very num to it. light. The aluminum alloys, which lighter the piston, the higher are the engine operating speeds. In casting, molten alumi- is poured into molds. Cast pistons are less expensive produce and are strong enough for most engines. In forging, dies. aluminum is hammered into shape between two is more expensive, but provides a stronger Forging and denser piston. Forged pistons are used in many en- STUD HOLES CYLINDER WALLS COOLING FINS CYLINDER HEAD CAST IRON LINER Figure 7-2. Twin cylinders for a four-stroke cycle (one cylinder cut away). (Honda Motor Co., Ltd.) SPARK PLUG SHORT STUD CYLINDER HEAD CYLINDER GASKET CYLINDER FLANGE CRANKCASE Figure 7-3. Long studs are used tfie cylinder and cylinder Motor Corp. U.S.A.) hiead. to fasten (Yamaha Figure 7-4. Sfiort studs or machine screws are used to fasten the flanged cylinder to the crankcase. Separate studs are used to fasten the cylinder head to the cylinder. (Honda Motor Co.. Ltd.) 77 UNIT 78 7: Upper-End Parts and Construction TRANSFER PORT HEAD LINER RING LANDS RING GROOVES BARREL COOLING FINS SKIRT EXHAUST PORT SLIPPER TRANSFER PASSAGE A Figure 7-5. with ports cast Figure 7-7. A sectional view (Honda Motor Co.. Ltd.) two-cycle barrel or cylinder (Honda Motor in. Co., Ltd.) a piston. of FLATTOP VALVE RELIEF. HEAD RING RING GROOVES-^ E-v ^^:^ LANDS OIL I RINC / ' BEL1 BELT HOLES Figure 7-8. Piston with (Honda Motor Co., Ltd.) ^SKIRT a head. flat-top VALVE RELIEF NOTCHES DOME SLIPPERS Figure 7-6. Parts tor (Yamaha Mo- of a piston. Corp. U.S.A.) gines equipped with turbochargers (as we shall see in a later unit). The parts of a piston are of the piston, which called the head. are machined A shown in may have many number of grooves in the piston to Figure 7-9. Piston with a domed head and notches for valve relief. (Honda Motor Co., Figure 7-6. The top different shapes, is Ltd.) called ring grooves hold the piston rings. The domed heads, which extend further into the combustion domed raised spaces between the ring grooves are called lands. chamber. Notches are often made The area containing the head to provide clearance for the intake and exhaust the rings and lands and the area below the rings is the ring belt, called the skirt. is The skirt area contacts the cylinder wall to guide the piston as moves up and down. Areas of the skirt called slippers be cut out to minimize cylinder contact area and A hole called the pin hole for the piston pin. In is most pistons the pin rectly on the aluminum surface of the force is is view of a piston In many the piston in may pistons the top the shape of the piston. Since great is power supported in the wrist pin area by what are called bosses. These are The top of may supported di- applied to the piston pin area during the stroke, the underside of the piston sectional air-fuel mixture bored through the piston shown in a Figure 7-7. be of several different shapes. is f^at (Figure 7-8). Higher com- pression pressures can be achieved by using pistons with section of valves (Figure 7-9). Piston heads are designed to it friction. in the bum the more completely. They often conform to combustion chamber to move the air-fuel mixture past the spark plug more efficiently during combustion. Two-stroke pistons (Figure 7-10) often have a rounded top. In addition, the skirt area of the piston away to control may opening and closing of the transfer Since the piston must be able to be cut ports. move up and down the must be made slightly smaller than the cylinder. The small space between the piston skirt and the cylinder wall is called the piston clearance, which var- cylinder freely, ies for different .005 inch). it engines from .025 to .125 mm (.001 to PISTON RINGS ROUND HEAD COMPRESSION PRESSURES Install 79 THRUST FORCES piston with "EX" toward EXHAUST THRUST FORCES OFFSET^, PISTON PIN (b) SYMETRICAL 7-12. Piston Figure thrust forces CUTAWAY SKIRT OFFSET pin on the piston controls offset skirt. (Honda Mo- tor Co., Ltd.) (SLIPPER) of the forces on the Figure 7-10. Two-stroke piston with a round head. (Honda Motor Co.. Ltd.) ing each stroke. The skirt area of the piston is piston in Figure 7- 12(a) different duris on a power and stroke. Notice the arrangement of the connecting rod much too If there is properly supported. It clearance, the piston will not be will make a knocking sound called piston slap as the skirt rattles against the cylinder wall. Piston slap can eventually lead to the breaking of the pis- we can have If there is too little clearance, As high combustion temperatures lem. piston heats and expands at a cast iron cylinder walls, ance to begin with, wedged if much in the cylinder. higher rate than the may cause This phenomenon is it little to clear- become called piston shown, the crankshaft and rod will pull or thrust the piston to the left side of the cylinder. The pin holes through the piston are often slightly offset on the piston (Figure 7-12 (b) ). from one side of the piston were located in the center, pulled to the left to the other. the piston If the pin hole would tend side during this crossover. to get Moving the pin toward the major thrust face causes the rod to pull the piston firmly against the cylinder wall, right reducing knocking. Most motorcycle engines solve the problem of piston by providing a piston skirt that is oval rather than round (Figure 7-11). An oval skirt prevents expansion across the larger diameter as the piston heats up. The result a piston that gets round, increasing the area of skirt con- with the cylinder with increasing heat. The the cylinder with over action that results when the connecting rod swings the piston has very expansion this down heat the piston, seize tact the rod in the direction forced is Piston pin offset reduces piston slap caused by the cross- seize. is the piston another prob- and the cylinder walls expand. Since an aluminum it As to control the thrust forces ton skirts. both crankshaft. piston skirt has the job of supporting and guiding the piston as it # speeds up, stops, and reverses direction for each of the two or four strokes of the cycle. The direction COLD Figure 7-11. The oval piston skirt gets round as heats up. (Yamatia Motor Corp. it U.S.A.) PISTON RINGS The piston a movable rings are installed in piston grooves to provide crankcase. The seal between the combustion chamber and the rings are made of cast iron or steel, so that they always press against the cylinder walls. Their main purpose is to prevent compression pressures from leaking around the piston into the crankcase. In most two-stroke cycle engines, two rings are norin the two grooves of the piston (Figure mally installed 7-13). A locking pin is installed in the groove to prevent the ends of the rings from rotating and catching in a transfer or exhaust port. The two rings are called compression rings. Both two- and four-stroke engines use compression rings. Pistons used in four-stroke engines have three piston rings. The top two bottom one ure 7-14). is seal compression pressures, and the used to control As we oil on the cylinder wall (Fig- shall see in a later unit, oil is mixed with gasoline in the two-stroke engine for lubrication. This UNIT 80 Upper-End Parts and Construction 7: KNOCK PIN tips away from the cylinder wall, except during The lower outside comer of the ring has the stroke. contact with the cylinder wall, and the lower inside of the ring forms an effective blow-by seal COMPRESSION RINGS power a positive comer in the ring groove. The compression rings in Figure 7-15 use a tapered outer face which does a good job of wiping oil from the cylinder wall on the upstroke. The oil control ring scrapes oil off the cylinder wall and directs the oil through the ring and into holes in the piston (Figure 7-16). Oil then flows through the piston holes and Figure 7-13. Two compression rings used piston. (Yamaha Motor Corp. mns back on a two-stroke made U.S.A.) in The into the crankcase. one piece, or it may oil control ring spring spacer and two rails (Figure 7-17). TOP COMPRESSION RING spacer is slightly larger spacer pushes the A 2ND COMPRESSIOI RING it as- spring is sometimes used behind a out against the cylinder wall with inthe second ring. two-stroke engines use a ring called a keystone ring (Figure 7-19, top), in which the top side of the ring slants or tapers PISTON down. The keystone design allows pressur- ized gases to force the ring against the cylinder wall before Figure 7-14. Two compression and one oil ring used on a four-stroke piston. (Honda Motor Co., Ltd.) movement be- tween the ring and piston breaks up the formation of car- the gases get behind the ring. control -i n~p 5 i: Id OILCONTROLRING The sliding OIL HOLES OIL RING RECTANGULAR TOP RING OIL SLOT When the creased pressure. The two-stroke piston shown in Figure Some CONTROL RING the cylinder, uniformly against the cylinder wall. rail 7-18 has an expander behind OIL in spring spacer or expander piston ring to push The spring around than the cylinder. sembled on the piston and can be be made up of an expansible GROOVE COMPRESSION RING WITH LOWER OUTSIDE GROOVE Figure 7-16. by the oil Figure 7-15. Cross-sectional view of three piston rings. (Honda Motor Co., Ltd.) scraped off the cylinder passes through holes in groove. (Honda Motor Co., Oil wall the piston ring ring Ltd.) means that a two-stroke piston does not require an oil con- trol ring. A cross-sectional view of a set of piston rings Figure 7-15. in lar in cross Many section, is shown top compression rings are rectangu- forming a simple mechanical seal against the cylinder wall. Since they are larger than the OIL CONTROL COMPRESSION RINGS RING cylinder diameter, they push out against the cylinder wall to provide a seal A when compressed rectangular groove is in the cylinder. cut on the lower outside or the upper inside edge of many piston rings, which causes the intemal forces of the ring to be unbalanced. is compressed to fit in the cylinder, the top When the ring of the ring face SPRING SPACER RAILS Figure 7-17. This set of piston rings has a three-piece oil control ring. (Yamaha Motor Corp. U.S.A.) CYLINDER HEAD 81 KEYSTONE RING GAS PRESSURE, BACK PRESSURE MOVEMENT SPRING EXPANDER Figure 7-18. A spring expander may be used behind a piston ring to increase its sealing pressure. (Honda Motor Co.. Ltd.) Figure 7-20. The keystone ring moves in its groove to prevent ring sticking. (Honda Motor Co., Ltd.) KEYSTONE RETAINING RING PISTON RING RETAINING RING PISTON PIN RECTANGULAR PISTON RING Figure 7-19. A comparison between a rec- PISTON tangular (bottom) and keystone (top) piston ring. bon (Honda Motor Co., Ltd.) that could cause ring sticking. Figure CONNECTING ROD 7-20 shows a keystone ring, with tapered side. Figure 7-21. The piston pin is retained with two retaining rings or circlips. (Yamaha Mo- PISTON PIN tor The Corp. U.S.A.) piston pin, often called a wrist pin, connects the piston to the connecting rod (Figure 7-21). Since the full force of the combustion pressure is transferred from the piston to the connecting rod through the piston pin, the pin of high-quality steel. To cut down on weight, it is is made is method of installing the slightly smaller than the holes in the pis- ton and the connecting rod. It is therefore free to "float" both parts, but it is prevented from slipping or rotate in along length by two retaining rings or circlips, one on its could stick The advantage of in either the piston the assembly. The fit The cylinder head is an aluminum or iron casting mounted on top of the cylinder. A head gasket between the cylinder head and the cylinder forms a gas- and liquid-tight seal. Single-cylinder engines have a single cylinder head (Figure 7-22). Multiple-cylinder engines have either separate cyl- that the pin two or more heads cast in one piece. The combustion chamber above each piston is formed or rod without locking up by the inside surface of the cylinder head. Each combus- each side of the piston. The retaining rings in the piston. one of the closest and most pre- CYLINDER HEAD a free-floating piston pin in the piston and connecting rod. In this method, the piston pin is usually tubular rather than solid. Most engines use and the pin and piston cise in the engine. this design fit is into grooves or clearance between the pin and rod inder heads or tion chamber has a threaded hole for a spark plug. UNIT 82 7: Upper-End Parts and Construction UPPER ROCKER The combustion chamber for a two-stroke cycle engine is shown in Figure 7-23. The shape of the combustion chamber is round, so we call the design hemispherical. In many engines, a "squish area" is designed on the perimeter ARM INTAKE VALVES of the cylinder. This area forces the air-fuel mixture to flow past the spark plug stroke, at the making at the end of the compression for a near-complete burning of the mixture beginning of the power stroke. Cylinder heads used on four-cycle engines not only have a combustion chamber, but also must be equipped with in- EXHAUST VALVES take and exhaust ports together with a valve assembly to control the ports. There are two types of valve assemblies in common use: Figure 7-24. A pushrod engine with four valves per cylinder. (Honda Motor Co., Ltd.) pushrod valve systems and overhead cam- shaft engines. In a pushrod engine, the camshaft the cylinder may normally located in head area between cylinders (Figure 7-24). It is The camshaft operates a set of lower rocker arms which transfer camshaft movement through long hollow rods called pushrods. The pushrods then transfer the motion up to upper rocker arms which operate the valves. Pushrod engines use four also be located in the crankcase area. ROCKER ARM valves per cylinder, which increases their ability to get air and fuel in ROCKER SHAFT CAMSHAFT LOCK and exhaust gases out. RETAINER OUTER VALVE SPRING INNER VALVE SPRING SEAL GUIDE Figure 7-22. A cylinder head for a singlecylinder two-stroker. (Yamaha Motor Corp. U.S.A.) HEMISPHERICAL SPARKPLUG EXHAUST VALVE INTAKE VALVE CHAMBER Figure 7-25. An engine with an overhead camshaft. (Honda Motor Co., Ltd.) COMBUSTION The overhead camshaft engine uses one or two cammounted on top of the cylinder head. Figure 7-25 shows a single overhead camshaft. Rocker arms mounted SQUISH AREA shafts on rocker shafts transfer the camshaft motion directly to the intake and exhaust valves. VALVES Figure 7-23. A hemispherical combustion chamber with a squish area, (Honda Motor Co., Ltd.) The intake and exhaust valves both have a shaft called a stem that broadens into a large round valve head (Figure VALVE SEAT 83 VALVE STEM END VALVESTEM VALVE HEAD UIDE Figure 7-27. The valve guide is pressed into the cylinder head. (Honda Motor Co., Ltd.) uum in the cylinder the entire time the intake valve is open. VALVE SEAT STELLITE Figure 7-26. Parts tor of a valve. (Yamaha Mo- The valve Corp. U.S.A.) seat is a precision-ground area at the entrance of the valve port. 7-26) which has a precision-ground, tapered face that, when closed, seals against a seat in the cylinder head. When the face allowed to is pushed open by the rocker arm, gases are move around the valve head in or out of the cylinder. Valves are made of very high-quality get very hot during combustion. ally larger in The steel because they intake valve is usu- diameter than the exhaust valve because it must control the slow-moving, low-pressure intake mixture. Exhaust valves may be smaller because the exhaust gases leave the cylinder under higher pressures. Since the exhaust valve gets even hotter than the intake valve, made of even often used. it It may be a part of the cylinder head or a separate unit installed in the head with a press 7-28). If the cylinder head must be made of is in Figure 7-26 has its the valve seat matches the angle ground on the valve face, usually 45 degrees, although on some engines an angle of 30 degrees is used. gines also use an interference angle, which is Some a I en- -degree difference in the seat and face angles. Thus, the seat may be ground to 46 degrees and the valve to 45 degrees. Or the seat may be ground to 45 degrees and the valve to 46 degrees. The interference angle provides a hairline contact is n stem end and valve face hardened by plating with a hard metal called stellite. (Figure fit of aluminum, the seats cast iron or steel. The angle ground on higher-quality steel. Stainless steel alloys are The valve made -VALVE STEM SEAT WIDTH VALVE GUIDE The valve stem DETAIL is supported and guided in the cylinder head by a valve guide. Most engines use a guide that may be removed and replaced during an overhaul. Replaceable as may made of cast iron or a softer material such bronze alloy. They are usually pressed into the cylinder guides be ^ head (Figure 7-27). The clearance between the valve stem and the guide must allow free movement of the valve. It must also allow a small amount of oil to work its way between the stem and guide for lubrication. If there is too much clearance, oil from the rocker arm area could work its way down the stem and into the combustion chamber. This is especially a problem on the intake valve stem because there is a vac- VALVE SEAT ANGLE VALVE SEAT ^ SEAT WIDTH ^ VALVE FACE ANGLE Figure 7-28. The valve seat, which may be a separate part of the cylinder head, nnatches the valve face, (Detail: US. Suzuki Motor Co.) UNIT 84 7: Upper-End Parts and Construction VALVE GUIDE VALVE LOCKS VALVE RETAINER ' OUTER VALVE SPRING INNER VALVE SPRING VALVE STEM SEAL VALVE SPRING SEAT INTAKE VALVE EXHAUST VALVE A Figure 7-29. between the valve and valve spring and retainer assembly. (Honda Motor Co., Ltd.) seat for positive sealing and reduces buildup of carbon on seating surfaces. The width of the seat is the seat is too wide, there important for good sealing. If is a greater chance of carbon A buildup, preventing good seating. wide seat also spreads the valve spring tension over a larger area, thereby reduc- ing the seal. On retainer placed on top of is it. Two split valve locks or keepers are inserted into grooves cut into the valve stem the other hand, too narrow a seat will re- and fit into the retainer, locking the spring to the valve. A small "O"" ring seal in a groove on the valve stem prevents oil from running past the lock-and-retainer-cap as- sembly down the valve stem. Some engines use a torsion-bar-type valve spring (Fig- A duce heat movement away from the valve head and into ure 7-30). the coolant passages near the valve seat. chored VALVE SPRINGS, RETAINERS, AND SEALS open, an arm attached to both the valve and torsion bar moves with the valve, twisting the torsion bar. When the lower part of the cam contacts the rocker arm, the torsion at torsion bar is a length of steel bar that both ends in a holder. When bar untwists and returns the valve to A typical valve-spring-and-retainer assembly Figure 7-29. The valves are held in the is shown in closed position by the valve its is is an- pushed closed position. Rocker arms (Figure 7-31), which are usually made of cast iron, are mounted on and supported by a shaft con- valve springs, which are coil springs on most engines. nected to the cylinder head. Since the hole in the rocker When arm extra sealing pressure is needed, two springs, an in- The valve springs bottom of the spring on a are held in position rests directly steel spring seat. The spring is slightly larger than the diameter of the shaft, the rocker arm ner and outer one, are used. by a retainer. The on the cylinder head or is compressed, and the is free to rock end of the rocker arm is up and down. The valve stem usually adjustable for valve clear- ance. The rocker arm changes upward movement to down- KEY TERMS TORSION BAR 85 CAMSHAFT SPRING CRANKSHAFT SPROCKET TORSION BAR HOLDER 7-30. Torsion Figure (Honda Motor bar valve spring. Co., Ltd.) CAMSHAFT SPROCKET VALVE CLEARANCE ADJUSTER CHAIN Figure 7-32. The camshaft is driven by a chain connected to the crankshaft. A single overhead cam is shown. (American Honda Motor Co.) ROCKER ARM NOSE BASE CIRCLE HEEL CAMSHAFT 7-31. The Figure opens the valves. ward movement. If its arm roci a , 9^ 'T , N. Figure 9-20. Checking the cylinder head warpage. (Yamaha Motor Corp. U.S.A.) for side ring groove should be cleaned of carbon, Figure 9-22. Measuring the piston. (Honda Motor Co., Ltd.) gauge TOP-END SERVICING Figure 9-25. Checking the pin fit (Yamaha Motor Corp. U.S.A.) in 121 the pis- ton. -j! Figure 9-23. Measuring piston ring side clearance. (Harley -Davidson Motor Co., Inc.) Figure 9-26. Checl'cle Time . Total Stalled Flat-iaK Boodel Tune Time Special Tools, Equipment, Parts, and Materials Valve gniKkr Measuring scale References Mi::-:i:7_-?: 5 Shop Mamal _ Specifications jijzzn in the spaces hekrw. baake valve face ^z.t pThawct valve face 2zz.z InraW valve niin i u m — —^r- Fariiansr val^-e miiiiiiMim bstnidor dieck Procedure 1. Mount ifae protection stem of one of your valves in the V-bradcet of when using 2. Tom 3. Advance tbe 142 oo tbe machine %'alve ±e il-z zrjiii S.-JETi' CACTIOS': Alwavs wear the valve grinder.) said atj^nst the oocrfant stem totvaid tfae flow over the grs.is.z v^ied and grind just ^ -eel. aua^ ma:e- 1. stem to lesaiface it. e\e 4. Install the valve stem and chamfer the in the fixture tip. Instructor check 5. 6. Repeat steps 1^ for each of your valves. Adjust the valve grinding chuck to the correct angle for grinding the valves. Inspect the valve-face grinding stone. If it appears to require truing, check with your instructor. Instructor check 7. 8. Adjust the chuck sleeve and chuck stop to accept the valve stems. Install a valve in the chuck and adjust the carriage plate stop to prevent the valve neck from contacting the grinding wheel. 9. 10. 11. Turn on the grinder and adjust coolant flow over the grinding wheel. Move the valve into grinding position Move the valve and slowly bring the grinding wheel back and forth over the grinding wheel. Be sure not into contact with it. to let the valve face pass beyond the grinding wheel edge. 12. Move the grinding wheel toward the valve in small increments Be careful to remove the minimum amount of metal. 13. Back 14. Use 15. Grind each of the other valves and record the margin measurements the grinding until the face is smooth and shiny all the way around. wheel away from the valve and then move the valve carriage back out of the way. a measuring scale to determine whether the margin is still an acceptable width. Instructor check in the spaces below. Valves with thin margins must be replaced: Cylinder Intake Exhaust #1 #2 #3 - #4 Instructor check NOTES Instructor check Date completed 143 NAME DATE SECTION M Job Sheet RESURFACE AND TEST VALVE SEATS Before you begin: Read pp. Make of Motorcycle Time Started Flat-rate Model Time Finished Total Year Time Time Special Tools, Equipment, Parts, and Materials Valve seat cutter set Measuring scale Solvent Lapping compound Valve spring compressor References Manufacturer's Shop Manual Specifications Look up the following specifications for the engine and record them in the spaces below: Intake valve seat angle Exhaust valve seat angle Intake valve seat width Exhaust valve seat width Instructor check Procedure valve cutting pilot in the guide of the intake valve seat. 1. Install a 2. Select a valve cutter of the correct angle and diameter and install 144 it on the pilot. 3. Cut the valve seat just enough 4. Measure pilot the seat width and cut the seat to remove and compare until it is it all the pits. with specifications. If the seat is too wide, install a narrowing cutter on the the correct width. Instructor check 5. Repeat the grinding and narrowing procedure for each of the other valve 6. Measure and record the width of each of your valve Cylinder seats. seats in the spaces provided below: Exhaust Intake #1 #2 #3 #4 Instructor check 7. Use the spring compressor to install the valves, valve springs, and retainers. (SAFETY CAUTION: Wear eye protec- tion.) Instructor check 8. Pour solvent around each of the valve heads and watch for leaks into the intake exhaust or port. Instructor check 9. 10. If there is a leak, disassemble the valve. Place a small amount of valve lapping compound on the valve face and seat. Use a valve lapping cup to lap the valve into the seat. 11. Clean the lapping compound off the 12. Reassemble the valve and check it parts. again for leaks. Instructor check NOTES Instructor check Date completed 145 DATE SECTION NAME . M Job Sheet REASSEMBLE FOUR-STROKE UPPER END Before you begin: Read pp. Make of Motorcycle Time Started Flat-rate Model Time Finished Total Year Time Time Special Tools, Equipment, Parts, and Materials Piston ring compressor Feeler gauge Gasket set Piston ring set References Manufacturer's Shop Manual Specifications Look up the following specifications and record them below: Cylinder head nut or bolt torque Intake valve clearance (lash) Exhaust valve clearance (lash) Procedure on the Observe the markings 1. Install the piston rings 2. Space the end gaps of the rings 120 degrees piston. to get the correct ring in the correct groove right side up. apart. Instructor check 146 3. Install the pistons on the connecting rod using new circlips. Be sure that the pistons are in their original location and point in the correct direction. Instructor check new cylinder base gasket. 4. Install a 5. Oil the piston rings and cylinders. 6. Compress 7. Install 8. Install a the piston rings with one or chain guides or tensioners new if more compressors and push the cylinder over the pistons. required. cylinder head gasket in position. Instructor check 9. Place the cylinder head in position on the cylinder. camshaft 10. Install the in place. 11. Rotate the crankshaft into position for camshaft timing. 12. Align the timing marks on the camshaft sprocket and install the sprocket and chain in the camshaft. Tighten the sprocket bolts to the correct torque. Instructor check 13. Back 14. Oil the camshaft and install the camshaft holder in position. 15. Start all the cylinder off the adjustment screws on each of the rocker arms. head nuts or bolts and tighten them in stages. Follow the tightening order in your shop service manual. 16. Adjust the tension on the camshaft drive chain. 17. Rotate the engine into position on the intake and exhaust valve rocker arm on the heel of the camshaft. 18. Using the correct feeler gauge between the rocker arm and valve stem, adjust the rocker arm to 19. Repeat steps 17-18 for each rocker arm. set the valve clearance. Instructor check 20. Install a new gasket on the cylinder head cover, and install the cover. Tighten the cover nuts or bolts to the specified torque. 21. Install the exhaust, fuel, and ignition system components. NOTES Instructor check Date completed 147 UNIT 148 9: Four-Stroke Upper-End Troubleshooting and Servicing KEY TERMS 5. What should you look arm Valve clearance: space or lash low left in the valve train to al- for heat expansion. Valve clearance adjustment: the setting of the valve lash to that is reduced during each valve face grinding. 7. Describe face. Valve seat width: the width of the valve seat that gets 8. is not compressed. 9. 10. when it can you determine the amount of piston-to-cyl- Explain Why how to remove and replace valve guides. must valve guides be replaced before valve 1 1 How 12. Why 13. 14. is How seats are resurfaced? can you check a valve for sealing after lapping? valve seat width important to good valve is compressed to a specified What two measurements Why is the margin that are made on valve is left on a valve springs? after resur- facing important? Valve spring tension: the amount of pressure developed by the valve spring determine whether valve guides are sealing? Valve spring free length: The length of a valve spring it to inder clearance? wider during valve seat cutting. when how a camshaft? worn. Valve seat angle: the angle of the valve seat that must match the angle of the valve inspecting a rocker What measurements should you make on and the valve guide. Valve margin: the width of the unground head of the valve when 6. the correct specifications. Valve guide clearance: the space between the valve stem for wear? for 15. amount. Why must the camshaft and crankshaft be aligned during reassembly? CHECKUP 1. 2. List three Describe symptoms of upper-end problems. how to troubleshoot a cylinder by observing DISCUSSION TOPICS AND ACTIVITIES 1 a spark plug firing end. 3. How can you use a compression test to determine whether an engine has a ring or valve problem? 4. Why should you locate the cam and crankshaft tim- ing marks before disassembling the engine? Measure the compression of a four-stroke engine before and after top-end servicing. What are your results? 2. power of Compare the and top-end servicing. Did the power improve after noticeably? a four-stroke engine before In the discussion of engine parts and construction in Unit engine was divided into two basic areas: the upper end and the lower end (Figure 10-1). The lower end of the 7, the engine consists of a crankcase, crankshaft, connecting rod, crankshaft bearings, and connecting rod bearings. There are a number of types and designs of each of nents. In order to be able to troubleshoot these compo- and service lower ends for both two-stroke and four-stroke engines, a basic understanding of lower-end components cordingly, in this unit tion of engine we is required. Ac- describe the parts and construc- lower ends. JOB COMPETENCY OBJECTIVES When you be able and studying finish reading this unit, you should to: 1. Describe the purpose and types of crankcases. 2. Identify the parts of a crankshaft. 3. Explain the different crankshaft designs required for different cylinder arrangements. 4. Identify the parts of a connecting rod. 5. Describe the different types of bearings used in an engine. CRANKCASE The crankcase is the aluminum case or housing supports the crankshaft and houses ponents. It must be made in two all the lower-end parts so that it that com- can be dis- assembled for installation of lower-end components. Many smaller single- and twin-cylinder engines have a crankcase which ^ is divided or split vertically (Figure 10- 150 UNIT 10: SIDE Engine Lower End COVER SIDE OIL PASSAGES COVER i \ 2 ^ \ CRANKCASE CRANKSHAFT OIL PASSAGES Figure 10-4. Oil passages are cast and crankcase halves. (Honda Mo- drilled in the tor Co., Ltd.) Figure 10-2. A crankcase can be (split) vertically. (Bottom: or twist the crankshaft out of shape, heavy counterweights divided Honda Motor are attached to the crankshaft opposite the throws to bal- Co.. ance the weight of the piston and connecting rod assembly Ltd.) The crankshaft throws, with their connecting rods and when the crankshaft is rotating. Most motorcycle engines combine the flywheel and counterweights into one part. As shown piston assembhes, are very heavy, and the rapid rotation of the crankshaft increases the force that their weight exerts even further. Since the increased force tends to bend DIVIDING LINE o in Figure 10-5, the four-stroke crankshaft drives the valve operating A r~i camshaft drive sprocket } L mechanism by means of is o * £ Figure 10-3. A crankcase can be divided a chain. attached to the end or the cen- (split) horizontally. CRANKCASE ) HALVES CRANKSHAFT The crank pins. Each crank pin through the two counterweights and CAMSHAFT DRIVE SPROCKET fits of a connecting rod bearing, which big end of the connecting rod. CONNECTING machined as sepa- offset connecting rod journals are rate parts called The 151 is pressed through the center in turn fits inside the built-up design allows the use of a caged needle or roller bearing for the connect- ROD JOURNAL ing rod which MAIN BEARING required for the speed and lubrication re- is quirements of a two-stroke engine. The spacings of JOURNAL the throws on a multicylinder-engine DRIVE crankshaft are designed to allow a different stroke to occur SIDE in each cylinder at a given time. There is a wide variety of cylinder arrangements and crankshaft throw designs in use. The most common motorcycle engines have one, two, or four cylinders. Crankshafts for single-cylinder engines are simple, having just one throw and a main bearing jour- nal at either end. (Figure 10-7). TAPERED TIMING END COUNTERWEIGHTS MAIN BEARING JOURNALS Figure 10-5. Crankshaft for a two-cylinder (Yamaha Motor Corp. U.S.A.) engine. SMALL END NEEDLE BEARING Figure 10-7. Crankshaft for a single-cylinder engine. (Honda Motor Co., Ltd.) iH— CONNECTING CRANK ROD PIN END NEEDLE BEARING BIG / COUNTERWEIGHT (FLYWHEEL) COUNTERWEIGHT (FLYWHEEL) Figure 10-8. Twin side-by-side or in-line (Kawasaki Motors Corp. U.S.A.) Figure 10-6. An exploded view of a built-up crankshaft, (Yamaha Motor Corp. U.S.A.) cylinders. Twoter of the crankshaft. drive side, mission. is the crankshaft, called the used to deliver power The other end as the alternator. cated at this end, A One end of is to the clutch Since ignition components it is and trans- used to drive accessories, such may be lo- often called the timing end. 10-6. is shown in The counterweights have centers, exploded view in 10-8) or in a V-shape (Figure 10-9). These engines have their crankshaft Figure a shaft attached to their which form the crankshaft main bearing journals. throws arranged so that one piston at a time provides a power stroke. Most two-stroke twins have a crankshaft multipiece or built-up crankshaft for a two-cylinder (two-stroke) engine or twin-cylinder engines can have their cylinders arranged either side by side (called in-line; see Figure as shown in whose two throws are set 180 degrees apart, Figure 10-10. The reason is that a two-stroke twin with a 180-degree crankshaft has one piston going down on a power stroke while the other is going up, thus making the engine operate very smoothly. 152 UNIT Engine Lower End 10: SPROCKET CRANKSHAFT REAR BALANCER Figure 10-9. Twin with cylinders arranged in a V-shape. (Harley-Davidson Motors. Inc.) DRIVE CHAIN SHAFT' ^ mr~ Figure 10-12. Counterbalancers attached reduce vibration. (Honda Motor Co.. Ltd.) to the crankshaft to L WS THROWS -J Figure 10-10. Two-stroke twin with throws 180 degrees apart. (Honda Motor Co., Ltd.) CENTRIFUGAL FORCE ON COUNTERWEIGHTS CRANKSHAFT COUNTERWEIGHT Figure 10-13. Centrifugal force acts on the crankshaft counterweights. (Honda Motor Co., Ltd.) The four-stroke twin with a 360-degree crank is not a smooth engine because both pistons go up and down together, setting Figure 10-11. A 360 used on a four-stroke degree cranleartnc - outer 11 Oil seal and retainer 11 Oil seal spring ring 13 Shim 14 Shim crankcase assembly. (Harley-Davidson Motors. Inc) Figure 11-3. Separating crankcase halves. (Honda Motor Co., Ltd.) 161 CONNECTING ROD e~r Figure 11-4. Disassembling the multicylinder crankcase parts. (Honda Motor Co., Ltd.) 162 LOWER-END SERVICING BEARING 163 OIL SEAL BEARING OILSEAL OILSEAL OILSEAL LEFTCRANKCASE OILSEAL Figure 11-5. Bearings and seals in a vertically Before you remove any connecting rod caps, carefully observe each connecting rod for factory match marks indicating their position. Not all engine manufacturers mark It is extremely important to stamp unmarked connecting rods on both the cap and rod during removal. Use a hammer and punch to mark the cap and rod. You can mark one mark for #1, two marks for #2, and so on. Remove the connecting rod cap nuts and then the rod caps. Take care not to scratch the crankshaft journals the connecting rods. vertically split crankcases contain a ber of ball bearings and oil seals (Figure the seals them fication is Clean 1 1-5). num- Remove and discard them. Remove the bearings and place in containers marked to identify each bearing. Identi- important for later inspection and possible reuse. all the crankcase crankcase^ (Yamaha Motor Corp. U.S.A.) type of crankshaft must be disassembled for parts replace- ment. You can measure components in cleaning solvent, and allow them to air-dry on a clean rag. After any ball or worn. You can judge this by feel. Check for the correct connecting rod big-end side play feeler gauge between the crank counterweight (flywheel) and the rod big end. Compare your measurement with specifications. In (.024"). If it it should be between exceeds the .3 mm latter value, the connecting rod big end should be closely checked for excessive wear. In addition, total crankshaft width should be measured. measurement If either Remove Inspection and measurement: Built-up crankshaft is beyond the specification, the the pump pump gear locating pin (lo- gear, and square primary drive gear key small two-stroke engines use a built-up crankshaft. to determine drive gear, cated in a hole in the shaft), thick washer, primary drive the particular number of checks can be made most cases, .6mm (.012") and crankshaft must be disassembled for parts replacement. to prevent rusting. Many at to determine the (.08"), the big-end bearing is eye or needle bearings have been cleaned, they should be reoiled A connecting rod axial looseness amount of wear in the big end (the crank pin and big end bearing). Hold the big end stable to prevent it from sliding, and then rock the small end as shown in Figure 11-6. If the play exceeds 2 mm end the small (Figure 11-7). Slide the big end to one side and insert a with the rod cap studs. The halves of split whether this slip 1 fit 1-8) model you are if they occur on working on. Both gears are a on the crankshaft end, but the gear puller (Figure may be able to be used to aid in their removal. Do 164 UNIT 11: Lower-End Troubleshooting and Servicing "A" 2 mm OR LESS ml) Hh V Figure 11-9. Pressing out the crank (Yamaha Motor Corp. U.S.A.) Figure 11-6. Checking the big-end bearing (Yamaha Motor Corp. U.S.A.) 0.3-0.6 CRANK mm pin. PIN CON-ROD (.012"-.024") CRANK PIN BEARING CRANK PIN SHIM Figure 11-7. Measuring big-end side clearance. (Yamaha Motor Corp. U.S.A.) RIGHT SIDE OUTER FLYWHEEL LEFT SIDE OUTER FLYWHEEL 11-10. Disassembled (Yamaha Motor Corp. U.S.A.) Figure Figure 11-8. Claw puller used pulling for crankshaft. neath the right-hand crank counterweight (flywheel), and gears. (Harley Davidson Motors, Inc.) press the crank pin out of the supported wheel. Finally, support the left hand counterweight (flywheel) not use a screwdriver or chisel to pry the gears off, as gear and press out the crank pin. Figure 11-10 shows a disas- teeth can be chipped. sembled crankshaft. Use a hydrauHc press to press off the left-hand crank If any evidence of damage is found on the crankpin or counterweight (flywheel). This pressing procedure requires big-end connecting rod bearing, both bearing and crankpin a crankshaft support fixture (available from each motorcy- are normally replaced. cle manufacturer). wide enough A length of pipe with an inside diameter to slip the crank into should be squared and can be used. Pipe ends smooth. Cut a These are usually sold as a kit along with the shims or thrust washers on each side of the rod. To reassemble the crankshaft assembly, support the slot the entire right-hand outer crank counterweight (flywheel) with the length of the pipe wide enough for the connecting rod to pin installed; then install the rod bearing and connecting fit through. Drop filed the crank into the fixture, place support plates beneath the left-hand outer crank wheel, the crank pin out of this Remove wheel (Figure 1 and push square or straightedge to accurately line up both wheels, 1-9). the connecting rod and rod bearing, rod, with the crank pin pointing up. Position the left-hand counterweight (flywheel) over the pin, use a machinist's lift the re- maining crankshaft section up, place a support plate be- and tap the left wheel down onto the pin wheel from moving out of alignment. to prevent the LOWER-END SERVICING Press counterweight left-hand the down onto (flywheel) 165 straight you reach the specified width. The wheel must be pressed straight down, or the pin will enter the hole on a slant, resulting in damage. the pin until Lay a straightedge across both counterweights (flyat two points 90° opposite the crank pin. Both wheels must be parallel to each other. If they are not, tap the high wheel with a brass hammer. Finally, align each wheels) crank half before pressing both halves together. Inspection and measurement: One-piece crankshaft After the parts of the one-piece crankshaft are cleaned, Figure 11-11. Measuring a crankshaft nal. (Yamaha Motor Corp. U.S.A.) they can be inspected and measured for wear. Carefully check each journal for any signs of scoring. Place the mm crankshaft on a bench under a strong light, and look over .03 each main and connecting rod journal for any signs of tioned. The scoring. shorten the slightest score on a crankshaft journal can new main of a life or connecting rod bearing. journals pass a visual inspection, they should be If the measured. Crankshaft journals are measured with an outside micrometer (Figure 11-11). Select a micrometer with Look up the specifications for main bearing and connect- ing rod journal diameters in the shop manual, and write them down rag to for reference. make Wipe the journals with a clean sure that they are free of oil and dirt. Also, wipe off the measuring surfaces of the micrometer to make sure there is no dirt on them to cause an error in the of the crankshaft and measure the Start at the front di- ameter of the connecting rod journal for cylinder number Make I. the end the measurement about 6 mm away from (.25") of the journal, to ensure that the micrometer does not measure the small radius, called a where the fillet, journal meets the throw. Record this measurement. and record another measurement journal. Make and same journal at at the Make other end of the record two more measurements of the 90° from the first two measurements. a measurement Should you find a difference between taken at one end of the journal and one taken end, the journal is probably tapered. ence between two readings taken the journal ally is find surement with the crankshaft journal specifications from the shop manual. A journal mm cation by .03 that is at If you at the other find a differ- 90° from each other, out-of-round. Connecting-rod journals usu- wear out-of-round, because of the way the connecting worn under this specifi- (.001") will also have to be recondi- tioned. the rod cap is attached to the big end of the connecting rod (where the fits) is called the saddle bore. This area often wears out- of-round, because during the saddle bore is of the saddle bore load area. power stroke, the top of the is much not under The uneven load load, we call it a no- application eventually stretches A new stalled in a stretched saddle bore will vice insert bearing placed under a severe load. Since the bottom the saddle bore out-of-round. measurement. have to be recondi- (.001"), the crankshaft will The crankshaft may also be worn undersize. To out whether it is, compare your smallest journal mea- The big-end bore made when the correct size-range for the journals to be measured. joui- insert bearing in- have a very short ser- life. The saddle bore is measured for out-of-round by means of a telescoping gauge and an outside micrometer (Figure 11-12). Choose a telescoping gauge that will fit into the saddle bore and expand out against the cap and rod. Place the telescoping gauge into the saddle bore in a direction 90 degrees from the cap mating surfaces, and expand the gauge Then until there is a light drag against the saddle bore. tighten the handle and remove the gauge. Measure across the gauge with an outside micrometer, and record the measurement. Then place the gauge back in the saddle in a direction 90 degrees from the first measurement. bore Make sure the gauge does not contact either the mating surface between the rod and cap or any bearing lock make and record the new direction. measurement with rod applies force to the crankshaft. Repeat the measure- grooves, and ment procedure for each of the other connecting rod journals, and record all of your measurements. Repeat this same procedure for each of the main bearings, and record dle bore in out-of-round. these measurements. connecting rod has to be replaced. Check the specifications After you have completed your measurements, deter- mine the maximum out-of-round and maximum the worst journal. If the taper or out-of-round is The difference between in the a the Any measurable the sad- two measurements is the out-of-round means that the shop's service manual. taper for Carefully inspect the sealing surfaces of each of the larger than crankcase halves. Minor dents or scratches can be removed UNIT 166 11: Lower-End Troubleshooting and Servicing Wipe ameter. the crankshaft and insert bearing free of oil, mm cut a length of plastic string about 3 ( Vs.") shorter than on each bearing inside sur- Position the bearing holder over the crankshaft, and the bearing, and set the string face. recommended torque wrench readturn the crankshaft when you remove tighten the bolts to the ing. Be the bearing careful not to holder; the string plastic have been will squashed between the crankshaft and the main bearing You can now sert. in- determine the clearance, using the width scale on the string package. Match the stripes on the package with the flattened stripe has a clearance correct stripe is string (Figure 11-13). measurement printed on it. Each When found, read the measurement. This is the the clearance between the main bearing insert and the crank- Figure 11-12. Measuring the big end connecting rod for stretch. by using valve lapping compound and a shaft surface like a flat and Change from coarse forth, holding to fine lapping it on the flat compound the Move scored surface and place the crankcase on the glass. the crarikcase back glass. as the scrat- ches are polished away. size main bearing the lower end, select the correct- inserts. You must select main bearings called undersize because they are used with an undersize crankshaft. Bearing size usually printed on the bearing is box and on the back of the bearing. Always check the shop manual for the types and identification of available undersize bearings. new main bearing inserts into the bearing holder half. Be sure to wipe the caps and housings perfectly clean and dry main bearing clearance wrong is size. acceptable, the main bearing inserts Remove are ready for final assembly. and lift inserts should the bearing holder the crankshaft back out of the cylinder block. Oil each of the main bearing inserts in the crankcase with en- gine oil or an assembly lubricant. Assembly lubricant has is and will not leak out of the not to be started for a period of time after overhaul, assembly lubricant should always be match the crankshaft diameter. If the crankshaft has been ground undersize, the main bearings will have to be thicker to make up the space. These thicker bearings are Put the the bearings are the If the you measure a clearance is worn or If (.003"), then the crankshaft the consistency of thick grease that and into the crankcase mm bearing. If the engine Reassembly: Lower end To begin reassembling main bearing journal. larger than .08 compound on Put the lapping large piece of glass. of the first; used. Lubricate each of the main bearing inserts set the crankshaft into the main bearing inserts. Install the bearing holder and tighten the bolts to the final torque value specified by the manufacturer. The connecting rod big-end clearance is checked in the same way. Install a new insert bearing in each rod cap and rod, and put a piece of plastigauge on each crankpin, avoiding the oil hole. Install the bearing caps on the correct crankpins, and torque them to specifications. Remove the caps and measure the compressed plastigauge on each crankpin (Figure 11-14). The clearance should be less than the backs of the never be oiled or greased. Place the crankshaft in the crankcase on the new main bearing inserts. You are now ready to measure the oil clearance between the crankshaft and the main bearing inserts. Proper lubrication PACKAGE SCALE and cooling of the bearing depend on correct crank- shaft oil clearances. Scored bearings, a worn crankshaft, FLATENED excessive cylinder wear, stuck piston rings, and worn pistons may result other hand, if from too small an the oil clearance may pound up and down, is oil clearance. On PLASTIC STRING the too great, the crankshaft overheat, and weld itself to the insert bearings. Fine plastic string called plastigauge the oil clearance shaft. between the The plastigauge is is used to measure insert bearing relatively long and the crank- and has a small di- in the bearing holder, and each crankshaft journal. Then gently Figure 11-13. Compare the flattened plastistring to the scale on the package. gauge LOWER-END SERVICING .08 is mm 167 (.003"). If the clearance is larger, the crankshaft worn or the bearings are the wrong size. Oil the insert bearing and the connecting rod journal with clean oil. Install the rod cap in the correct position, always double-checking the factory match numbers. and tighten the connecting rod cap nuts Install to specifications. Repeat the procedure for each of the connecting rods. Install any new seals or ball bearings which fit in the crankcase halves, and then coat the sealing surfaces of the crankcase halves with the recommended type of sealant. Install any counterbalancers, chain guides, or cam chains removed during disassembly. Push Figure 11-14. Checking bearing oil U.S.A.) connecting rod clearance. (Yamaha Motor Corp. gether and install tighten all ommended all studs, fasteners to the sequence. the crankcase halves to- screws, and bolts. Finally, recommended torque in the rec- NAME SECTION Job Sheet DATE 6. On 7. Check each connecting rod a horizontally split crankcase, remove for factory the bolts which hold the bearing holder. Then remove the bearing holder. numbers and match marks. Mark the rods with a punch if they are not marked. Instructor check 8. Unbolt the rod caps and remove the rods. 9. Clean all parts in cleaning solvent for inspection and measurement. NOTES: Instructor check Date completed 169 NAME SECTION DATE \M Job Sheet INSPECT AND MEASURE THE CRANKSHAFT Before you begin: Read pp. Make of Motorcycle Time Time Finished Started Flat-rate Model Total Year Time Time Special Tools, Equipment, Parts, and Materials Outside micrometer References Manufacturer's Shop Manual Specifications Look up the following specifications for the engine and record them in the spaces below: Connecting Rod Journal: Standard diameter Maximum Maximum Undersize out-of-round Main bearing taper journal: Standard diameter Maximum Maximum Undersize out-of-round taper Instructor check Procedure 1. Wipe 2. Inspect each crankshaft connecting rod journal. Are the journals: the crankshaft bearing journals and the Smooth 170 Slightly scored main bearing housings with a clean Rough rag. 3. Inspect each main bearing journal on Smooth 4. If you the crankshaft. Rough Slightly scored find Are the journals: any scoring, the crankshaft will have to be reconditioned. Check with your instructor. Instructor check 5. Select an outside micrometer with the correct range for measuring the connecting rod journals. 6. Use the correct-size outside micrometer to measure each connecting rod journal. horizontal direction and at least is two in a vertical direction. The maximum Make at least two measurements in a two measurements difference between these the out-of-round. Write in your results below: Connecting Rod: #1 . #2 #3 #4 Maximum out-of-round Maximum taper Maximum undersize Instructor check Make the same measurements on each of the main bearings and record your measurements in the spaces below: Main Bearing #1 #2 #3 #4 8. Maximum out-of-round Maximum taper Maximum undersize Compare your measurements with specifications. If any of your measurements are beyond specifications, the crankshaft must be reconditioned. Instructor check NOTES Instructor check Date completed 171 NAME SECTION Job Sheet DATE . 5. Place the gauge back in the saddle bore about 90° from the mating surfaces. 6. Make first measurement. Make sure you are not contacting the another measurement. Repeat these measurements for each connecting rod, and write them in the spaces below: Connecting rod: #1 #2 #3 #4 7. The difference between the is the amount of out-of-round. The difference between your largest amount of oversize. Determine the out-of-round and write it in the space below: two measurements reading and the specifications is the Out-of-round 8. Compare the out-of-round measurements with specifications to determine whether the connecting rods should be re- placed. Instructor check NOTES Instructor check Date completed 173 NAME DATE SECTION Job Sheet ^n\ REASSEMBLE THE BOTTOM END Before you begin: Read pp. Make of Motorcycle Time Started Model Time Finished Total Year Time Time Flat-rate Special Tools, Equipment, Parts, and Materials References Manufacturer's Shop Manual Specifications Look up the following specifications for your engine and record them in the spaces below: Bearing holder torque Main bearing oil clearance Connecting rod nut torque Connecting rod bearing oil clearance Instructor check Procedure 1. If you are working on a vertically split crankcase, install new bearings in the crankcase and install the crankshaft assembly. you are working on a horizontally crankcase, begin by determining the crankshaft main bearing 2. If 3. Clean each bearing cap and housing, using a clean rag. 4. Place a 5. Place a main bearing insert in each of the main bearing positions of the bearing holder. 174 mean split bearing insert in each of the main bearing housings in the crankcase. oil clearance. 6. Carefully 7. Cut a length of plastigauge and lay 8. Install the 9. Compare lift the crankshaft into position in the crankcase. it on each main journal. bearing holder and torque the cap bolts to specifications. Remove the bolts and remove the bearing holder. the flattened plastigauge string to the stripes on the plastigauge package to get the clearance measurement. Write the clearance measurements in the spaces provided below: Main Bearing #1 #2 #3 #4 10. Compare your specifications, oil clearance measurements with specifications. If your measurements are larger or smaller than the check with your instructor. Instructor check 11. Wipe assembly 12. Place each main bearing cap in the correct location and direction. 13. Tighten 14. Check all lubricant on each bearing insert and main bearing journal. the bearing holder bolts to the correct torque in the correct sequence. the crankshaft for free rotation. If it does not turn freely, check with your instructor. Instructor check 15. 16. Place an insert bearing in the rod cap. Cut a length of plastigauge and position Place the cap in position on the rod and tighten the cap nuts to specifications. it on the connecting rod journal. Remove the cap and measure the width of the flattened plastigauge using the stripes on the package. 17. Repeat the procedure for each connecting rod and piston assembly, and record your results below: Connecting Rod #1 #2 #3 #4 18. Compare your clearance measurements with cations, check with your specifications. If your clearances are larger or smaller than the specifi- instructor. Instructor check and journal with 19. Coat each 20. Install each bearing cap and torque the nuts to specification. 21. Install any new 22. Replace any counterbalancer assemblies, chains, or chain guides that have been removed during assembly. 23. Put the 24. Push the cases together and tighten insert bearing seals that are required recommended sealer lubricant. on the crankcase halves. on the crankcase sealing surfaces. all fasteners to the recommended torque in the recommended sequence. Instructor check NOTES Instructor check Date completed 175 176 UNIT 11: Lower-End Troubleshooting and Servicing KEY TERMS Connecting rod bearing oil clearance: the space between the connecting rod journal and the connecting rod preci- 7. Explain how 8. How a built-up crankshaft disassembled? 9. What new Crankshaft out-of-round: a condition in which a crankshaft worn Main bearing shaft oil in an egg-shaped manner. preci- 12. measured with plastigauge. bearing and a journal to measure 13. oil clearance. Explain how How a connecting rod journal measured to deter- is to reassemble a built-up crankshaft. How is a connecting rod measured to determine Explain how to measure the crankshaft main bear- ings. 14. end of the connecting rod. How can minor scratches be removed from the seal- ing surface of a crankcase? 15. CHECKUP Describe on a built-up whether the saddle bore has stretch? Saddle bore out-of-round: the stretch or egg-shaped wear that occurs to the big parts are normally installed mine out-of-round? clearance: the space between the crank- Plastigauge: a plastic string placed in between an insert 1 10. 1 1 main bearing journal and the main bearing sion insert; measure big-end side clearance. crankshaft? sion insert bearing; measured with plastigauge. journal has is to How is the connecting rod bearing oil clearance mea- sured? how to troubleshoot an engine for abnormal noise. 2. Explain how check to a lower end by moving the connecting rod. 3. 4. Explain How how to check a lower end for an can a pressure stroke crankcase 5. tester vacuum oil leak. be used to locate a two- Explain the steps to follow in splitting crankcase Why should you never use a screwdriver to pry crankcase halves apart? 1. leak? halves. 6. DISCUSSION TOPICS AND ACTIVITIES Measure a connecting rod saddle bore with an insert bearing installed, and then measure the crankshaft journal the rod fits on. How can you determine the oil 2. clearance? Measure the oil clearance of the same rod and crank- shaft with plastigauge. How does this oil clearance measurement compare with your first one? Which method do you think is more accurate? Vyil circulated between is moving parts of the engine to prevent the metal-to-metal contact which causes wear. Oil between moving parts allows them less friction. The lower the internal the more power it to move friction easily, with of an engine, can develop. The circulating cools oil by carrying heat away from hot engine compoalso cleans or flushes dirt and deposits off the en- the engine nents; it on the cylinder walls improving the engine's compression. We the components used to circulate oil the lubrication gine parts. Finally, oil circulated seals the rings, call system. In this unit, we describe the types and operation of two- and four-stroke lubrication systems and how to ser- vice them. JOB COMPETENCY OBJECTIVES When you be able 1. finish reading and studying this unit, you should to: Explain the relationship between lubrication and LUBRICATION SYSTEM OPERATION AND SERVICING fric- tion. 2. Describe the parts and operation of a wet and a dry OIL SUPPLY four-cycle lubrication system. 3. Describe the parts and operation of a premix and an oil injection 4. Change two-cycle lubrication system. the oil and filter element on a four-cycle en- gine. 5. Prime the oil injection pump on a two-cycle oil injec- tion system. FRICTION One of AND LUBRICATION main purposes of the reduce friction. Friction that are moving is OIL FILM the lubrication system a resistance between to is Figure 12-1. An oil film between the shaft and bushing prevents metal-to-metal con- two objects against each other. If you push a book tact. along a table top, you will notice resistance due to friction. The rougher friction, a weight to move the table and the book surface, the greater the because the two surfaces tend to lock together. is it placed on the book, takes even it more If effort across the table. This illustrates two important points about friction: ( 1 ) The smoother the two surfaces of As the amount of pres- the objects, the less the friction. (2) two objects increases, them increases. We want to reduce the amount of sure between as much between the friction were to pour a slippery liquid such as our hypothetical book would engine friction in an between little resistance. oil to (Figure 12-1) that about .05 to .08 gether fast. The friction to- between the skin on your hands causes the skin to get hot. We cannot eliminate friction completely, but reduced so that longer engine life may be it can be expected. If we oil is a shaft supported by a bushing slightly larger than it. The slightly larger size of the bushing leaves a small space, usually oil. friction table top, reduce metal-to-metal contact between engine parts. Also, friction between two surfaces causes them to heat The heat generated by on a would form a thin layer book off the table surface, and thereby reducing the friction between the book and the table. In a similar manner, we use a film of very engine parts, the more power the engine can develop. may be demonstrated by simply rubbing your hands oil across the table with called nfilm under the book, lifting the As an example, consider as possible since the lower the friction and, consequently, to wear. The move Oil is mm (.002 to .003"), that we can fill with directed under pressure into the oil clearance area of the bushing, whereupon the oil pressure and the ro- form and wedge between the shaft and the bushing. The shaft thus rests not on the bushing, but on the film of oil, leaving no metal-totation of the shaft cause a film of oil to metal contact. Hence, the friction has been reduced as much as possible. 177 UNIT 178 12: Lubrication System Operation and Servicing FOUR-STROKE LUBRICATING OIL oil is a chemically complex fluid that is refined from petroleum or synthetic materials. The oil used in a motorcycle engine must have the correct viscosity and ser- Lubricating vice rating. The oil. A fluid is is Oils used in engines must flow freely in cold conditions, rust, like SAE 20, while thicker oil receives a SAE 40 OR SAE 50. The viscosity number is printed on top of the oil can (Figure 12-2). 20 SAE 30 in the posits, rust, summer and SAE A multiple-viscosity oil like SAE 10-40 SAE 10 when the weather is cold, but SAE 40 when it is hot. A motorcycle ridden SC service provide minimum for SD service provide more protec- SE service provide more protec- tion against oil oxidation, high-temperature engine de- The in the winter. API describes the in gasoline engines. SE. Oils designed for • or motorcycles use for the lowest rat- and low-temperature engine deposits, wear, rust, and corrosion in engines than do SC oils. SD oils may be used when API Engine Service Category SC is recommended. should be used. Many list is tion against high- motorcycle owner's manual usually specifies which viscosity and corrosion SD. Oils designed • The Society of Automotive Engineers (SAE) has set up oil receives a low viscosnumber, SC control of high- and low-temperature deposits, wear, standards for oil viscosity. Thin ity The following the highest. SC. Oils designed for but be thick enough during times of high temperature. higher number, like SF ing, very thick. Low-viscos- High-viscosity fluids flow sluggishly. SC, SD, SE, or SF ratings. the thickness or thinness of the with a high viscosity ity fluids are thin. letters gasoline-powered engines. Currently, • viscosity of an oil by the ratings are designated SD oils. and corrosion SE may oils classifications are SC SD engines than do either in be used when either SC or recommended. SF. Oils developed for SF service provide increased • flows freely like oxidation stability and improved antiwear performance protects like relative to oils that needs a multiple- viscosity in different climates that a viscosity rating with a means that the oil W after with that rating it, is oil. Note SAE 20W, like capable of cold- may be and SC oil can is an engine given oil Institute (API), are a and corrosion, and used when any of the classifications SE, SD, are recommended. oil's service rat- ing (Figure 12-2). Serice ratings, set up by the Petroleum for provide protec- oils also tion against engine deposits, rust, (winter-) temperature operation. Also printed on the meet the minimum requirements API Service Category SE. SF American measure of how well a holds up under severe servicing conditions. The TWO-STROKE LUBRICATING OIL In the discussion of engine operation in Unit 6, mentioned that air cycle engine and then cylinder. was it and fuel enter the crankcase of the two- move up the transfer port into the Most two-cycle engines are lubricated by bring- ing oil into the crankcase along with the air and fuel. To must be mixed with the gasoline. This mixing can be done outside or inside the engine, as we bring VISCOSITY it in, the oil shall see later. Two-cycle lubricating of SERVICE RATING oil that long time. The mixture Some oil (Figure 12-3) is a special type mixes with the gasoline and stays mixed is for a different for different engines. engines use 15 parts of gasoline for each part of Others use a 25-to-l mix, part of oil. There is i.e., oil. 25 parts of gasoline to one always more gasoline than oil in the mixture. FOUR-STROKE LUBRICATION SYSTEMS Four-stroke which cycle engines use oil is directed lubrication. Figure 12-2. The viscosity and service ing are printed on an oil can. rat- system in to the parts that require There are two basic types of these pressure brication systems: wet A a lubrication under pressure lu- sump and dry sump. dry-sump lubrication system uses two pumps and separate tank on the motorcycle to store the oil. a One pump forces oil through the engine parts and the other pump re- FOUR-STROKE LUBRICATION SYSTEMS turns it to the oil tank. system because there is The system 179 called a dry-sump only a small amount of oil in the is sump. The dry-sump system has the advantage of provid- more oil can be stored in end of most small-engine crank- ing a large supply of oil because the tank than in the lower cases. In the in the the wet-sump system (Figure 12-5), the oil is stored bottom of the crankcase. The one pump required system picks up and delivers it oil to the in from the bottom of the crankcase components that require lubrication. After lubrication, the oil runs back into the crankcase by gravity, to be stored for later use. Both the wet- and dry-sump systems have about the same lubrication system components and internal oil flow route. filter, The Figure 12-3. Two-cycle lubricating oil must mix with gasoline^ (Chevron Chemical Co.) turns the oil to the oil tank. are shown in The Figure 12-4. The above the engine, so oil parts of a dry oil tank is Each system has an and drilled oil that sump system usually located flows by gravity into the high- pump, which forces the oil through the engine The lubricating oil then runs down to bottom of the engine into an area called a sump. The oil pressure oil Figure 12-4. sump and A dry-sump oil enters the pump first passes through a wire- re- lubrication pump causes the oil to flow throughout the en- While there are many pumps, the rotor pump is used on many wet-sump systems, it is common to have both different types of the pressure then pulls the oil out of the pump, gine, resulting in a pressure buildup. engines. In pump pressure strainer, pressure scavenger oil strainer flow channels and galleries. which prevents any large particles of foreign material from entering the lubrication system. The screen parts for lubrication. the oil The pump and the scavenger pump in one housing. pump is mounted on the bottom of the rotor-type crankcase and driven from the primary shaft through a system (Honda Motor Co., Ltd.) -^^ ROCKER ARM ROCKER ARM CAMSHAFT 'VERTICAL GALLERY ' ftn ORIFICE OIL PRESSURE SWITCH A- CRANKSHAFT ^^^^^ ^ REAR BALANCER MAIN OIL GALLERY TRANSMISSION MAIN SHAFT COUNTERSHAFT ORIFICE n ns ^ OIL FILTER OIL PUMP i^ n OIL STRAINER PRESSURE RELIEF VALVE _L_ Figure 12-5. Typical wet-sump lubrication system. (Honda Motor Co.. Ltd.) 180 It FOUR-STROKE LUBRICATION SYSTEMS 181 INNER ROTOR OIL FILTER ELEMENT I I ORING ORING CENTER BOLT Figure 12-6. Rotor-type Motor Co., Ltd.) oil pump. (Honda Figure 12-8. Oil Motor Co., Ltd.) SPRING SEAT SPRING CASE filter (Honda assembly. FLOW ROUTE BACK TO CRANKCASE OIL FLOW OIL CRANKCASE IN OIL FILTER CASE OIL OUT OIL FILTER FLOW ELEMENT RELIEF VALVE PLUNGER SPRING Figure 12-7. The gear. The pump shown in Co., Ltd.) The pump by the engine and an outer rotor driven by the inner As VALVE Figure 12-9. Cross-sectional view (Honda Motor Co., Ltd.) rotor. it large forced through the outlet. is During engine operation, the oil pressure opens the oil leak stopper valve to maintain oil flow, and when the en- gine stops, the valve closes to prevent flow from the oil tank. The leak stopper valve used only is in wet-sump sys- The rotor pump has a relief valve assembly mounted on valve is The purpose of 12-7). outlet side (Figure to prevent too high a pressure the relief from forming in the system. The unit consists of a small plunger backed up by a calibrated spring. plunger some is oil If the pressure pushed into position becomes too high, to release pressure, the sending back into the crankcase. As soon as the pressure an oil '"O" A ring. center bolt and "O" ring hold the case to the crankcase. The 12-9. oil filter The any dirt shown in cross section in Figure made from paper. When oil is treated paper that the element is made element filter is element routed through the of, tems. of filter. pulled in and carried around between the is rotor lobes until its BY-PASS the rotors turn, the lobes separate, causing a partial vacuum. Oil CENTER BOLT Figure 12-6 consists of both the pumps, a leak stopper valve, and a is made up of an inner rotor driven delivery and scavenger relief valve. valve prevents too relief (Honda Motor high a pressure. and acids is in the oil stick to the outside of the paper, and only clean oil gets through. After the oil goes through the filter element, it returns to the crankcase to be circulated into the engine components. After a period of use, the oil filter element may become clogged with materials that have been filtered from the oil. If oil no longer passes easily through the element, it no longer gets to the engine parts. To prevent this problem, a assembly. When returns to normal, the relief valve spring repositions the bypass valve plunger. element becomes clogged, the pressure inside the canister increases and pushes open the bypass valve. The After the it the passes through the oil goes to the tion of the filter gine parts. The the crankcase, filter element is to clean the oil before filter where is pump and relief valve, assembly (Figure 12-8). The func- oil filter assembly it housed is is it typically reaches the en- mounted onto The accessible for replacement. in a removable case sealed with a oil is located inside the filter filter then goes around the filter and directly into the main oil gallery. Some engines use a centrifugal type of oil filter (Figure 12-10), consisting of a set of vanes attached to a rod driven by the engine. When the engine is running, the UNIT 182 12: Lubrication System Operation and Servicing up on the there made OILOUT ;;^oiL Markings on the dipstick show whether The dipstick on the oil tank is usually of the oil tank cap, as shown in Figure 12- dipstick. enough is as part oil. 13. IN TWO-STROKE LUBRICATION SYSTEMS There are two basic types of lubrication system used on two-stroke engines. VALVES Figure 12-10. A centrifugal-type (Honda Motor Co., Ltd.) oil mixed together filter. mixes tion type The premix type uses in the oil gasoline and oil motorcycle fuel tank. The oil injec- with the air and fuel as they enter the engine. The premix vanes spin. Oil enters the and filter is picked up by the lubrication system is the simplest type and does not require any special components. The rider simply spinning vanes, whereupon foreign matter such as metallic adds the correct amount of two-stroke dust and carbon particles are separated from the oil by cen- mix up the fuel. Some motorcycle shops sell fuel already mixed with oil. The premix encounters the air moving through the car- The cleaned trifugal force. oil fed to the engine parts is through the outlet port in the center section of the filter cover. When buretor and mixes with the oil leaves the filter assembly, it enters the oil passages of the crankcase, flowing into several long chan- From nels called galleries. oil main the gallery, oil flows to The crankshaft clearance areas at main bearings. drilled nals to from the main journals promote oil flow. The connecting rods to the piston are ing area. Oil up sent is After the may oil up drilled lengthwise reach the piston bush- vertical galleries in the cylinder the engine back to the it falls or runs sump. Oil up on down the inside of makes that way its in the piston, the cylinders and lubricating passes through oil control ring from where sump. The path of oil it is allowed to fall flow for typical engines oil back oil holes to the shown is in Figures 12-11 and 12-12. oil lubrication system. This switch mounted near is oil oil pres- provided from an ignition mounted on level, the sending unit The oil the crankcase, senses en- below a safe provides a ground and a completed if the pressure drops circuit lights the oil pressure indicator light. If the oil level is provide enough too low, the pump oil for lubrication. will not be able to Oil level with a dipstick inserted into the crankcase tank. The higher hand, if too simple, it has several disad- much added, the engine will smoke and oil is the spark plug will be fouled with carbon and the engine will run poorly. To avoid these problems, many two-stroke motorcycles, on the street, have a separate tank for especially those used oil and an engine oil injection is measured sump the oil level, the higher the oil will or oil come system of metering the in just the correct amount. A pump is oil into the used to force from the oil tank into the crankcase and to control the amount of oil delivered (Figure 12-15). The pump forces oil from the oil chamber. The pressure switch must provide a path to ground. gine oil pressure, and is does not add enough oil, the engine parts will not receive enough lubricant and can quickly wear out. On the other connected to a warning switch terminal. In order to have a complete circuit, the pressure switch unit, While the premix system sumption the tachometer. is forced into the is necting rod large ends, and cylinder, thereby lubricating part of the is sure warning light warns the rider of low oil pressure. Current for the indicator light mixture final air-fuel each component. oil to the engine pressure switch (see Figure 12-5) light usually form the crankcase and goes through the crankcase bearings, con- out thrown off the is them, as well as the piston and ring assembly. Excess picked up by the to air-laden mixture excessive carbon will build up on engine parts. Eventually, of each of the connecting rod bearings crankshaft, splashing it oil to the fuel in the to vantages. If the rider mixes the prelube incorrectly and has passed through those parts of the engine oil that require lubrication, The (Figure 12-14). to the connecting rod jour- sometimes bushing so that is head to the camshaft and rocker arms. An and shakes the bike fuel tank An oil tank into the crankcase in exact proportion speed and load, resulting and pump less carbon buildup for an oil injection system The pump is mounted at case with a screw. The pump drive ure 12-16. fitted to the cam in in reduced the is oil con- combustion shown in Fig- the top of the crank- gear, which is press engine crankshaft, rotates the drive shaft. The drive gear at the other end of the drive shaft rotates gear. The pump itself consists of a plunger, a pump body, and springs. Two-stage cams, inside and outside, are formed on the side surface of the cam gear. The inside cam is for the plunger, the outside one for the valve. The valve and plunger are held against the cam surfaces by means of the springs so that they move up and down in the pump body as the cams rotate according to the rotation of the cam gear. the cam valve, a TWO-STROKE LUBRICATION SYSTEMS OIL PUMP 183 H RIGHT CRANKCASE CYLINDER CYLINDER HEAD RIGHT CRANKCASE COVER CLUTCH ADJUSTING BOLT Figure 12-11. The operation of ure 12-17. At point Oil flow in typical the valve and plunger A, the valve is at blocking the discharge port and the the intake port opens, and oil is shown pump port. in Fig- At point B, pump housing due to the creation of a vacuum as the plunger goes down. At point C, the end of the intake stroke, the valve starts rising in the body, blocking the inlet port. As the valve rises further, the pump housing opens SIDE COVER CENTRIFUGAL OIL FILTER CAMSHAFT — CRANKCASE CRANKSHAFT — CRANKCASE motorcycle engines, (Honda Motor Co, Ltd.) bottom dead center, flows into the RIGHT CYLINDER HEAD to the discharge port (point D), and the plunger is pushed up by the cam. Oil is then forced into the inlet pipe, overcoming the check valve spring force (point E). Lubricating oil flows through the system as shown Some in Figure 12-18. oil injection systems control the flow of oil the accelerator grip as well as with engine speed. shown in Figure 12-19, the oil pump gine through a reduction gear and is is with As driven by the en- connected to the car- 2. Camshaft Camshaft 3. Valve Lifter 4. Valve 5. Piston 6. Piston Pin 12. Oil 7. Connecting Rod 13. Oil Screen 1. Figure 12-12. 184 8. Main Bearing 9. Crankshaft 15. Bypass Valve 10. Starter Gear 16. Output Shaft 11. Oil Pressure 17. Drive Shaft 18. Big 19. Camshaft Chain Svifitch Oil flow in Pump 14. Oil Filter End Bearing motorcycle engine, (Kawasaki Motors Corp. U.S.A.) FUEL TANK ,'///////;///j//j////j/ OIL AND FUEL MIXTURE FILLER CAP DIPSTICK CARBURETOR UPPER LEVEL MARK LOWER LEVEL MARK SPECIFIED LEVEL Figure 12-14. The oil and fuel are mixed in the fuel tank on premix lubrication systems. (Honda Motor 7yyyy/y//^//777777 DRAIN PLUG Figure 12-13. The determine the oil to 2.0-3.0 kg-m (15-22 oil tank dipstick level. is (Honda Motor Co.. Ltd.) FUELTANK ft.-lb! used -^- OIL TANK Co., Ltd.) Figure 12-15. A separate oil pump is used on an oil injection system. (Honda Motor Co., Ltd.) OIL PUMP VALVE PLUNGER - CAM GEAR CAM DRIVE GEAR SCREW PUMP DRIVE GEAR Figure 12-16. Oil pump assembly used on an oil injection system, (Honda Motor Co., Ltd.) 185 UNIT 186 12: Lubrication System Operation and Servicing (SUCTION STROKE) A (DISCHARGE STROKE) C B Figure 12-17. Operation of the oil D injection pump. (Honda Motor E Co., Ltd.) FUEL TANK OIL PUMP Figure 12-18. Oil flow through the oil injecsystem. (Honda Motor Co., Ltd.) tion buretor throttle cable controlled by the throttle hand grip. The pump automatically regulates the volume of oil cording to the engine speed and throttle valve opening, thus pumping the optimum amount of cation under any operating condition. oil for LUBRICATION SYSTEM SERVICING ac- engine lubri- Servicing the four-stroke lubrication system involves draining the engine oil and changing the filter. The oil and filter should be changed regularly. Note that the intervals sug- TROUBLESHOOTING GASOLINE TANK 187 rider allows the tank to run dry, air will get into the oil lines THROTTLE CABLE A and pump air is pump. This must be removed before the The procedure to remove the bleeding or priming the pump. Usually, oil air will operate properly. called the engine is turned off and the delivery line at the oil pump is oil to run from the tank to the pump. Always follow the loosened while the throttle held open, allowing is exact priming procedure outlined in the shop manual. TROUBLESHOOTING Various troubleshooting procedures are recommended in different shop service manuals. BANJO BOLT only a diagnostic guide DELIVERY LINE manufacturer' some of 1. gested by the motorcycle manufacturer should be consid- by changing the the engine oil miles to the riding of is done if most of the or under conditions in which a in traffic dirt is likely to of life even more frequently. Oil should definitely be changed more frequently lot enter the engine. when Oil should be drained it is engine If the hot. of is and water will have time to stick to parts of the en- dirt The oil is changed best after a long ride. can be drained into a flat pan. If the bike has a the sump and tape the tank. under the it oil sump, you remove Oil feed 4. Restricted oil lines or fittings. 5. Restricted oil filter, Engine Uses Too Much Smokes Excessively 1. Remove Valve guides or valve guide crankcase or plugs and correct and torque them place a pan under the to spec- filter cover, al- the old filter element and replace filter Two-stroke the oil pump amount of recommended oil tank. Start the oil is or an oil line is worn. Engine Leaks Oil from Cases, Push Rods, Hoses, Etc. 1. Loose parts. oil engine and observe to all the drain at gaskets, push rod cover, washers, etc. Excess Oil Out of Crankcase Breather (Air Cleaner) 1 Oil not returning to oil tank. 2. Oil lines or passages restricted. 3. Gearcase cover gasket not sealing. 4. Leakage between passages and pockets 5. Excess Oil Out of Crankcase Breather When Starting Engine pump check 1. Oil 2. Poor seal ball stuck open. between feed and return gears oil the gearcase Restricted oil return line to tank. systems do not require changing consumed in the engine. If the removed from the engine, or if in cover and gearcase. it case for leaks. oil injection because seals Restricted breather hose to air cleaner. the center bolt (or bolts) to the correct torque. the worn or broken. Piston rings badly 3. 4. oil into new one. Then remove the old ""O" rings and innew ones. Replace the cover and install and tighten Add Breather valve incorrectly timed. 2. a cardboard flume, with a stall Oil or Restricted oil return line to tank. the center bolt or side bolts, and pull off the oil to dry. it filter. Imperfect seal cover. Clean the cover thoroughly in solvent and filter low the for pump gear key sheared. pump not functioning. Scavenger 3. 3. ifications. To change is Tank 2. tank drain plug, and direct the the oil pan. Install the drain plugs sequence following the If will You can make recommends have to drain both wet sump, place the pan under the crankcase drain plug. the motorcycle has a dry course, any checklist Oil tank empty. 2. cool, the oil will be too thick to drain well, and panicles gine. Oil Of never foolproof. Often, two the models: Oil Does Not Return to Oil Corp. U.S.A.) maximum; you can add many is LUBRICATION SYSTEM Figure 12-19. An oil injection pump connected to the accelerator grip. (Yamaha Mo- ered the it and even three conditions can be causing the problem. One OIL PUMP tor — 'Harley-Davidson Motor Co., Inc. in pump. NAME DATE SECTION [M Job Sheet CHANGE FOUR-STROKE OIL AND FILTER Before you begin: Read pp. Make of Motorcycle Time Started Model Time Finished Total Year Time Time Flat-rate Special Tools, Equipment, Parts, and Materials Torque wrench Drain pan New filter element Oil References Manufacturer's Shop Manual Specifications Look up in the the recommended amount of oil required for this engine when the oil and filter are changed. Record the amount space provided below: Capacity Look up the following torque specifications: Oil tank drain plug Crankcase drain plug Oil filter case center bolt Instructor check Procedure 1. Does this wet sump motorcycle have: (check one) dry sump Instructor check 188 2. Warm 3. Place a pan under the crankcase drain plug. 4. Remove 5. If the the engine to normal operating temperature. the plug and allow the motorcycle has an oil tank, through the flume and into the (SAFETY CAUTION: Be careful— the oil to drain. oil construct a flume out of cardboard, position it oil is hot.) under the oil tank, and direct the oil pan. 6. Remove 7. While the 8. Remove the filter center bolt and the 9. Remove the old the oil pan drain plug and allow the oil to drain. oil is draining, locate the filter. filter filter Put a pan under the oil filter case to catch the oil that will come out. case. element and compare it to the new one. Are they the same? Instructor check 10. Clean the 11. Wipe 12. Using new "O" rings, install the 13. Torque the filter case center bolt to specifications. 14. Add 15. Start the oil filter case assembly in cleaning solvent and allow the area the filter the is mounted on recommended amount of engine and check for new in the filter it to dry. crankcase with a clean rag. element and filter case. the correct type of oil to the crankcase or oil tank. oil leaks. Instructor check 16. Turn the engine off and check the oil level with the dipstick. NOTES Instructor check Date completed 189 NAME DATE SECTION Job Sheet \M. PRIME A TWO-STROKE INJECTION PUMP Before you begin: Read pp. Make of Motorcycle Time Started Rat-rate Model Time Finished Total Year . Time Time Special Tools, Equipment, Parts, and Materials Two-stroke oil References Manufacturer's Shop Manual Specifications Procedure 1. Look up the procedure for priming the 2. Remove the oil injection 3. Bleed the pump pump on this model motorcycle in the shop manual. cover. Instructor check oil inlet line by loosening a bleeder screw on the line at its connection on the pump or by removing the line. 4. Allow 5. You may have 6. Retighten the bleeder screw or line connection. 7. Bleed the oudet lines by loosening the connections the oil to flow out of the bleeder hole or the line until all air bubbles stop. to hold the pump open by hand and turn the pump plunger by cranking the engine. Instructor check 190 at the engine. 8. Crank the engine and allow 9. Retighten it to run at low RPM for a short period of time until all the air is expelled. Instructor check all line 10. Reinstall the oil 1 Check 1 connections and pump refill the oil tank, if _ necessary. case cover and tighten the screws to the correct torque. the system for oil leaks. NOTES Instructor check Date completed . 191 UNIT 192 12: Lubrication System Operation and Servicing KEY TERMS Dry-sump system: a four-stroke lubrication system with a pump separate oil tank and a scavenger the tank after it to return oil to between moving parts. oil to the What is a scavenger the purpose of a relief valve Identify the parts of the oil names pump on on an oil a dry- pump? assembly by writing filter spaces provided. in the 4. 5. 6. engine's parts. Oil: petroleum- or synthetic-based fluid used to provide lubrication. 7. 8. Oil filter: a device to filter out dirt and other foreign matter 9. oil. 10. Oil injection system: a two-cycle lubrication system in which oil from a separate oil tank is injected into the en- gine and mixed with the air and fuel. Oil level indicator: a dipstick inserted into the measure the Oil 3. their Lubrication system: a system designed to provide from What is the purpose of sump system? has been used in the engine. Lubrication: reduction of friction in an engine by the provision of oil 2. pump: oil pan 11. What 12. What happens when 13. a device used to circulate oil to the moving pressure in the lubrication system. Service rating: a system of rating up under wear and troleum becomes Identify the parts of the two-cycle oil injection their names in the spaces pro- vided. 14. 15. 16. how tear; established the oil filter element does a two-cycle premix lubrication system system by writing of an engine. Relief valve: a spring-loaded valve used to regulate the How work? parts Premix lubrication system: a two-stroke lubrication system in which oil is mixed with the fuel in the gasoline tank. the purpose of the oil filter? clogged? to oil level. is well an oil stands by the American Pe- 17. 18. Institute. 19. Viscosity: the thickness or thinness of an oil. Wet-sump system: a four-cycle lubrication system in oil is stored in the which crankcase of an engine. 20. DISCUSSION TOPICS AND ACTIVITIES 1 Why must the type of lubricating system is used on most two- stroke engines under conditions where dirt CHECKUP 1. What ily enter the oil well with gasoline? used in a two-stroke engine mix 2. engine? Why is this Using a shop four-cycle engine, of lubricating oil may eas- system used? try to trace the flow through the lubricating system. combustion I he that takes place in the gine cylinders generates a great used to push this heat is down motorcycle en- amount of Most of heat. the pistons, but a part of goes into the engine parts. Thus, a cooling system is it re- remove excess heat that might damage these The heat generated by combustion may be removed quired to parts. by either air we cooling or liquid cooling. In this unit, scribe the operation de- and servicing of the cooling system. JOB COMPETENCY OBJECTIVES When you be able 1. finish reading and studying this unit, you should to: Explain how heat is COOLING SYSTEM OPERATION AND SERVICING removed from air-cooled engine parts. 2. Describe the parts and operation of a liquid cooling system. 3. Explain the procedure used to locate a cooling system CYLINDER WALL problem. 4. Pressure-test a liquid cooling system. 5. Drain and refill coolant, and debug a radiator. COOLING FINS COOLING SYSTEMS AIR Most motorcycles, and all two-strokers, use an air cooling system. In such a system, components which get the hottest, fins HEAT such as the cylinder and cylinder head, have cooling formed around their outsides (Figure 13-1). pose of these cooling The puramount fins is to direct the greatest of air into contact with the greatest amount of hot metal. When the engine is head and cylinder and then moves out into the cooling fins. Aluminum, an especially good conductor of heat, used wherever possible. Air flows around the cooling carries away HEAT LOST TO AIR running, heat builds up in the cylinder the heat, as shown in is fins and Figure 13-2. Figure 13-2. Heat passes and air carries away. fins, Air draft. is into the cooling it directed around the cooling fins by the natural As the motorcycle moves, it pushes through the air (Figure 13-3), causing the air to flow over the motorcycle and through the cooling fins. as long as the motorcycle motorcycle air, is is There is a natural flow of air moving. However, when the running but not moving, there and parts can overheat. When is no flow of riding or testing an air- cooled motorcycle, you should avoid long periods of running the engine with the bike stopped. LIQUID COOLING SYSTEMS The advantage of an Figure 13-1. Cooling fins are formed on thie outside of the cylinder and cylinder head. (Honda Motor Co., Ltd.) as long as there the air cooling heating. is air cooling system adequate air is that it is simple: flow over the motorcycle, system can prevent engine parts from overlarge V-twin motorcycles have a built- However, 193 UNIT 194 13: Cooling System Operation and Servicing RESERVOIR TANK CYCLINDER HEAD PASSAGES RADIATOR PRESSURE CAP FRONT RADIATOR OUTLET Figure 13-3. Movement of the motorcycle through the air creates a natural draft flow over the engine. (Yamaha Motor Corp. PIPE THERMOSTATIC VALVE U.S.A.) in cooling der problem: some of the flow to the rear cylin- air Figure 13-4. Parts of the liquid cooling sys(Yamaha Motor Corp. U.S.A.) blocked by the front cylinder. Liquid cooling sys- is tems have been developed to solve The this tem. problem. THERMOSTATIC VALVE system circulates liquid around hot liquid cooling engine parts to carry off the heat. Coolant passages sur- round each cylinder and are placed in the cylinder impeLLER LANTPUMP L head very close to the valve area. Heat from the burning airfuel mixture passes through the metal of the cylinder head and cylinder wall and enters the cooling passages, where it then passes into the liquid coolant that circulates through the passages. Having entered the liquid coolant, the heat is then dispersed into the air through the radiator. The main advantage of a liquid cooling system can dispose of more heat than an An additional advantage duce engine noise, so is air is that it cooling system can. that liquid cooling passages re- OIL SEAL much BEARING engine operation that is quieter. The a liquid cooling coolant pump, system (Figure 13-4) radiator, thermostatic is made up of valve, radiator SHAFT hoses or pipes, radiator pressure cap, and reservoir tank. Figure The coolant is circulated by an impeller-type pump mounted on the right-hand crankcase and driven by a gear. It is drawn by the pump from the bottom tank of the radiator, directed through the outlet pipe, and discharged around the cylinder and cylinder head through the joint pipe. The coolant passes from 13-5. Sectional v\evj pump. (Yamaha Motor Corp. by a coolant pump seal that is of coolant U.S.A.) supposed to prevent coolant from getting on the bearing. the cylinder to the cylinder head through coolant passages and, after circulating around Radiator combustion chamber passages, enters the radiator upper tank via the inlet pipe. The coolant pump drive shaft is driven by a crankshaftdriven gear. The shaft is connected to a small wheel or impeller with blades that (Figure 13-5). its As is located in the coolant passage the impeller spins, center and throws it it draws coolant into off the blades by centrifugal force, causing the coolant to be pulled in and pushed out of the The heat removed from the hot engine parts by the coolant must then be removed from the coolant itself. This is done by pumping the hot coolant out of the engine and into a heat exchanger, The commonly referred to as the radiator (Fig- removes heat from the coolant so that the coolant may go back through the engine without fear of any engine parts being damaged by heat. Mounted in front of the engine, the radiator is made up ure 13-6). radiator pump. The shaft that drives the pump is supported on a bearing which is sealed to prevent coolant from entering. of a top tank, a bottom tank, and a center core or heat ex- A changer. bypass hole is provided to return any coolant that gets A radiator cover with air passages is mounted in LIQUID COOLING SYSTEMS 195 RADIATOR PRESSURE CAP RADIATOR TOP TANK AIR PASSAGES RADIATOR COVER BOTTOM TANK CENTER CORE Figure 13-6. The radiator acts as a tieat exchanger. (Yamaha Motor Corp. U.S.A.) front of the radiator to protect Hot coolant is pumped tank of the radiator. It it and direct air through it. out of the engine and into the top then enters the radiator core through number of small distribution tubes that are made from a metal that is a good heat conductor, usually copper or aluminum. The heat passes out of the liquid and into the a large wall of the tubes, which are fitted with copper or alumi- num air fins. takes the heat Air circulated through the core past the fins The cooled liq- from the fins (Figure 13-7). uid then runs into the bottom tank of the radiator, where it Figure 13-7. Flow of coolant and air through a radiator core. (E.I. DuPont de can be drawn back into the engine to pick up more heat. Nemours & Co.) Electric fan As long is as the motorcycle is adequate circulation of During long periods of moving through air idle, the air. there ature about 3° F. Thus, a cap that places the coolant at 12 through the radiator core. pounds pressurization raises its boiling point from 226° F (109° C) to approximately 260° F (126° C). however, there through the core, and the engine larger engines use an electric to pull air may is no air overheat. motor attached flow Some to a fan blade through the radiator core. The fans typically The radiator pressure cap performs two The pressure valve determines radiator cap will open. The valve vacuum work on a temperature-sensing system, so they rotate only during idle and warm conditions. A fan is shown in Figure the pressure at 13-8. spring tension. Radiator pressure cap this level is not valve. which the presses against a seat in the radiator The at 212° F (100° C) antifreeze-water solution will boil at about If the overflow tube into the reservoir tank. The vacuum valve normally remains closed, sealing the air. The system is under constant system from the outside steam and expand violently, so that it could easily damage the radiator or engine. The purpose of the radiator pressure until the engine into and raise the Each pound of pressure to pressurize boiling temperature of the coolant. that the open the valve. As long as reached, the pressure valve stays closed. If allowed to boil, the coolant will turn is neck under the valve opens, coolant or steam pressure escapes through At atmospheric pressure, water will boil pressure cap (Figure 13-9) filler tension of the spring determines the level of pressure required to and a 50-50 226° F (109° C). simple valves: a pressure the design and operation of valve and a function through its cap "holds" will raise the coolant boiling temper- pressure descrease. Then is shut down and temperature and the valve opens, allowing air to enter the system. If the valve did not open, the pressure drop would create a vacuum that could collapse the radiator or its hoses. 196 UNIT 13: Cooling System Operation and Servicing CD « e 9 «t r-v (9 SD Sl4Il Figure 13-8. Electric fan used The pressure to relief valve in the radiator an overflow tube that is hooked cap is to cool the radiator. connected to a clear plastic reser- (Honda Motor Co., Ltd.) between them (Figure 13-10). voir allows you to add coolant, A if cap on top of the resernecessary. voir tank. During pressure relief, the coolant goes through the tube and into the reservoir. cooled off, the coolant vacuum and is When drawn through the system has the overflow reenters the radiator. Lines on the reservoir tank allow a visual inspection of the coolant level. There is a "full line" and a "low Thermostat by line"; the coolant should be The thermostatic valve, or thermostat, the coolant system. regulates its It is a control valve in senses the coolant temperature and flow, automatically opening and closing de- LIQUID COOLING SYSTEMS 197 VALVE SPRING WAX PELLET Figure 13-11. Motor Co.) SPECIFIED RELIEF PRESSURE A thermostatic valve. (Ford VALVE CLOSED OVERFLOW TUBE BYPASS PASSAGE MAIN PASSAGE VACUUM VALVE PRESSURE VALVE Figure 13-9. Radiator pressure cap. (Ford Motor Co.) 3- CAP Figure 13-12. Thermostatic valve with main valve closed on a cold engine. (Yamaha Motor Corp. U.S.A.) ^M^^ ,^,:,vX'^ BYPASS Figure 13-10. Reservoir tank allows a visual inspection of coolant level. (Yamaha Motor MAIN Corp. U.S.A.) pending on the temperature of the engine. ant temperature closed. When the cool- below minimum, the thermostat remains is The coolant recirculates through a by-pass passage which is back into the engine usually located near the thermostat, or, at times, in the thermostat itself. The most common thermostat in use is the cold expansion wax pellet type, which closes when cold (Figure 13- When 11). the engine is cool, the thermostatic valve closed, but the passage to the by-pass is — Figure 13-13. Thermostatic valve open for warrr engine. (Yamaha Motor Corp. a warm U.S.A.) is open. Thus, the coolant does not flow into the radiator, but rather, flows Coolant through the bypass hose and the bypass valve into the coolant pump, where is it pumped to the engine cylinder As soon as the coolant ant passages (Figure 13-12). to the wax-filled pellet The coolant used of distilled water and antifreeze. Plain water which the thermostat will open, the expands, overcomes the spring pressure, temperature at and opens the valve for normal cooling action (Figure 13- The coolant then flows into the radiator. The thermostatic valve is installed in the water pump cover. Remove the cover to reach and remove the thermo13). stat (Figure 13-14). 50-50 percent mix coolheats in most systems an excellent coolant because of is its a is considered heat-transfer capabili- ties. However, water freezes at 32° F (0° C) and boils at 212° F (100° C), which limits its use as a coolant. If only water in is used, and it does freeze, it will expand about volume. The pressure of the expanding ice 9% can exert forces that can crack soldered radiator seams. Also, plain water can cause rust formation. UNIT 198 13; Cooling System Operation and Servicing WATER If engine PIPE is cold. Cooling systems with a reservoir tank be inspected for proper coolant level by simply observing (Q\ / ^\/^\^ O-RING / THERMOSTAT the level in the tank. HOUSING tic, Most tanks When you add SENDING UNIT are made of a clear plas- with lines that show the proper coolant level. coolant, do not through the radiator cap. ~'*^-' TEMPERATURE^*' when the may can damage the engine. Check the coolant level 0-RING it through the reservoir cap, You add coolant through the when you have drained and are (Safety Caution: Remember that the radiator cap only refilling the system. radiator cap keeps the coolant under pressure to raise T point. If the cap coolant THERMOSTAT may boil is opened when the engine boiling its is hot, the and overflow. Open a radiator cap with caution.) THERMOSTATIC Radiator pipes or hoses connected to the radiator carry SWITCH and from the engine. the coolant to THERMOSTAT COVER Remove the water pump tures, the coolant is Figure 13-14. cover to reach the thermostat. (Honda Motor dumped If one of the hoses rup- out very quickly. Old hoses become so stiff and brittle that vibration can cause them to even break. Check all hoses carefully for signs of cracks — Co., Ltd.) a small crack can soon cause trouble. Replace any cracked The majority of high-quality antifreezes available are hose. Poor coolant flow ethylene glycol based, fortified with rust and corrosion in- A 50% hibitors. water, 50% ethylene glycol lowers the freezing point of water to about solution - 34° F - 37° ( the thermostat may be due at too to a thermostat that fails high a temperature. Accordingly, must sometimes be removed from its hous- ing for testing. C). Ethylene glycol also raises the boiling point of water. 212° F (100° C), but when ethylene Plain water boils at glycol to open or opens to added is to -34° F ( - 37° it down for protection against freezing C), the boiling point increases to 226° F (109° C). If boiling does occur, the water boils off first, increasing the concentration of ethylene glycol. Find out the temperature the operation of the thermostat tainer of coolant. AND SERVICING system is on such a system. more complex and may A is never any liquid cooling (Make by putting sure that it it inside a con- does not rest A liquid cooling system that far above air it, replace the thermostat. flow across the radiator core is another cause of the engine's overheating. Radiator fins clogged with bugs, paper, or other debris from the road can reduce air flow. require troubleshooting not operating correctly is engine to overheat. Most liquid cooling sys- tems have a temperature sensor somewhere in them that is connected to a warning light near the tachometer. The warning light comes on when the engine's temperature too high. Other signs that the engine is is overheating are the engine's knocking or pinging under a load and the radiator's If THERMOSTAT venting steam from an overflow. you find that your engine is overheating, first check low, the overheating the coolant level. If the level is be due to a loss of coolant. Make may a visual check of the system to find any external leaks. Check all relevant hoses, pipes, and radiator clamps, the radiator core, and the radia- tor drain. In general, the coolant level in the radiator should be checked regularly. Overheating due to insufficient coolant on the The thermostat valve should open near its rated temit fails to open near that temperature or opens and servicing. will allow the will perature. If Poor Since an air cooling system has no parts, there servicing to perform which the thermostat bottom of the container.) Then heat the coolant and check its temperature with a cooking thermometer (Figure 1315). COOLING SYSTEM TROUBLESHOOTING at open by checking the shop service manual. Begin testing Figure 13-15. Testing a thermostat. (Honda Motor Co., Ltd.) COOLING SYSTEM TROUBLESHOOTING AND SERVICING PRESSURE GAUGE PRESSURE COOLING SYSTEM TESTER PUMP HANDLE 199 GAUGE PRESSURE PUMP RADIATOR CAP Figure 13-17. Pressure-checking the radiator cap. (Honda Motor Co., Ltd.) cified pressure (the pressure written on the gauge. cap If the fails to on the cap) reached is hold the pressure, replace it. RADIATOR FILLER NECK Figure 13-16. Pressurizing the cooling sys- tem Use an air to check from the engine air Bugs and other debris Wear eye protection.) will thereby be forced out. Clearing these passageways at least every few months will greatly improve the operation of the cooling system. may result from too much corrosion and and cylinder head coolant pas- sages. The any from the system, loss of coolant poor coolant flow, poor to may air be caused pump by warm engine while squeezing the reYou should feel a surge of pres- running a turn (top) radiator hose. sure as you let go of the hose. Clogged coolant tubes in the radiator flow, resulting in overheating. scale buildup in the cylinder Poor heat flow find may be due by a bad coolant pump. Check the operation of the coolant out through the radiator side. (Safety note: you do not flow, or poor heat flow. Poor coolant flow for leaks. (Chrysler Corp.) hose to gently blow If overheating heat developed in the cylinders and combustion then turn tor. It it off. Warm may slow coolant up the engine and Test for obstructions by feeling the radia- should be hot along the top and tom. Cold spots in the radiator mean warm along the bot- that sections of it are chambers cannot flow properly through a barrier of corro- clogged. Clogged radiators should be replaced or serviced sion and scale. This condition should be suspected at a radiator of the other troubleshooting procedures fail if all to reveal the If visual shop to remove the obstructions. prevent a buildup of scale and corrosion, coolant should be drained periodically and the system problem. inspection fails to show the cause of coolant must be pressure-tested. Put a cooling system pressure tester on the radiator filler neck loss, To the cooling system (Figure 13-16) and use the handle on it to pump the pres- manual into the system. A gauge shows the pressure. If the pressure fresh, clean coolant. pletely. Then Allow the engine to cool locate the radiator drain plug filled on the radiator bottom tank, place a pan under the drain plug, and remove the plug. Remove the radiator cap also, in order to provide sure specified in the shop a vent and allow the system to drain faster. After on the side of the coolant has drained out, replace the drain plug. tester drops on the gauge, there You should is an internal or external leak. then repeat the visual check because, with the system under pressure, it is likely that the source of the A radiator pressure cap that fails to hold the specified pressure can cause the coolant to boil off. the pressure cap with the same tester You can check you used to check the system pressure. Place the radiator cap on the end of the tester (Figure 13-17) and ommended amount pump the handle until the spe- of antifreeze water (usually a 50-50 mix), and the radiator filler disconnecting leak can be seen. with down com- its neck. solution refill and all Mix the rec- distilled the system through drain the reservoir bottle by Then bottom hose. Start the engine, and after it has warmed up, check the system for leaks. Allow the engine to cool down, and then check the coolant level in the reservoir. Add coolant to the up to the correct reservoir as necessary to bring the system level. NAME DATE SECTION EO Job Sheet PRESSURE-TEST A LIQUID COOLING SYSTEM Before you begin: Read pp. Make of Motorcycle Time Started Flat-rate Model Time Finished Total Year . Time Time Special Tools, Equipment, Parts, and Materials Pressure tester References Manufacturer's Shop Manual Specifications Look up the cooling system pressure and write it in the space below: Pressure Instructor check Procedure 1. Allow engine 2. the engine to cool off, is Install the and remove the radiator cap. (SAFETY CAUTION: Do not remove a pressure cap if the hot.) pressure tester on the radiator filler neck. Instructor check 3. Pump 4. Does the tester up to the specified pressure. the pressure: Hold steady Drop slowly Instructor check 200 5. Install the radiator 6. Pump 7. Does pressure cap on the pressure tester. the tester to the pressure rating on the cap. the radiator cap: Hold the specified pressure Fail to hold the specified pressure Instructor check 8. Remove the tester and reinstall the pressure cap on the radiator. NOTES Instructor check Date completed 201 NAME DATE SECTION Job Sheet . EEi DRAIN COOLANT AND DEBUG A RADIATOR Before you begin: Read pp. Make of Motorcycle Time Started Flat-rate Model Time Finished Total Year . Time Time Special Tools, Equipment, Parts, and Materials Drain pan Antifreeze coolant Air hose Distilled water References Manufacturer's Shop Manual Specifications Look up the following specifications: Cooling system capacity Mix of antifreeze and water Instructor check Procedure 1. Allow the engine 2. Place a pan under the radiator drain plug. 3. Remove coolant.) 202 to cool off. the radiator pressure cap. (SAFETY CAUTION: Make sure the engine is cold to avoid burns from hot 4. Remove it the radiator drain plug to drain the coolant. (SAFETY CAUTION: Coolant solution is poisonous. Swallowing can cause serious illness or death.) 5. Allow enough time 6. Replace the drain plug. Torque the plug 7. Using a clean container, mix antifreeze and 8. Pour the coolant mixture into the radiator through the radiator cap opening. 9. Replace the radiator cap and to completely drain the system. Drain the reservoir tank by removing the bottom hose. if required. Instructor check 10. Check warm up distilled water in the correct proportions. the engine. for coolant leakage around the drain plug. Instructor check 1 1 Stop the engine and allow 12. Add the necessary it to cool off. amount of coolant to the reservoir tank to bring the system up to the correct level. Instructor check 13. Use a shop 14. Check air hose and gently blow through the radiator core from the engine side out. the radiator core to be sure that all bugs have been removed. NOTES Instructor check Date completed 203 UNIT 204 13: Cooling System Operation and Servicing KEY TERMS Coolant: liquid used in a liquid cooling system to carry heat away from the engine; usually a mixture of ethylene glycol and water. Coolant pump: pump used to circulate coolant around hot engine parts. Cooling fins: metal move heat fins used on air-cooled engine parts to away from the parts. Cooling system: an engine system used to keep the en- gine's temperature within limits. Pressure cap: the cap on the top of the radiator that to regulate radiator pressure is used and vacuum. Radiator: a large heat exchanger located in front of the engine. Reservoir tank: a system connected to the radiator that catches overflow and sends Thermostat valve: a device it back into the in the radiator. cooling system used to Identify the parts of the coolant names control the flow of coolant. in the pump by writing their spaces provided. 11. 12. 13. CHECKUP 14. 15. What is the purpose of cooling fins on an air-cooled main advantage of an cooling system? engine? What is the air Identify the parts of the liquid cooling system writing their names 16. by in the spaces provided. 4. 5. 6. 7. 8. 9. 10. UUr^ DISCUSSION TOPICS AND ACTIVITIES Identify the parts of a radiator the spaces provided. 17. by writing their names in 205 DISCUSSION TOPICS AND ACTIVITIES 1. Using the shop manual for a liquid-cooled motorcyyour choice, look up its coolant capacity, cool- cle of 18. 19. 20. ant type, 2. Why and thermostat heat range. do most four-cylinder, gines use air cooling? in-line motorcycle en- w. hen the two-stroke piston uncovers the exhaust port, or when the four-stroke exhaust valve opens, the exhaust gases must be routed out of the engine. exhaust system to maintain is to provide for a maximum The purpose of the smooth flow of exhaust engine performance, while minimiz- ing exhaust noise. When the hot exhaust gases leave the cylinder under high pressure, the leftover energy in these gases can be used to drive an air pump pose of the turbocharger called a turbocharger. The pur- to force the air into an engine's is cylinders on the intake stroke. If the pressure of the intake system is raised above atmospheric pressure, enter the cylinder. With more air can can be burned more completely and the engine's increased. In this unit, we more air in the cylinder, fuel power output EXHAUST SYSTEMS AND TURBOCHARGING describe the parts and operation of exhaust systems and turbochargers. JOB COMPETENCY OBJECTIVES When you be able 1 finish reading this unit, you should A Describe the parts and operation of a four-stroke ex- muffler joint assembly. diameter runner pipe to the larger diameter muffler. and describe the operation of a two- stroke exhaust system. The purpose of Describe the basic operation of a turbocharger. 4. Identify the parts of a turbocharger. to quiet sectional pressure. the muffler down is to allow the exhaust gases the engine noise at the view of a muffler figure, the Explain the operation of a wastegate to reduce boost reducing cone joins the small- an area over which to expand before they exit the system, and 3. 5. of which are extremely important for good exhaust flow. The runner pipe is attached to the muffler through a haust system. Identify the parts 2. and studying to: is shown same time. A Figure 14-2. In the in exhaust gases flow into a large chamber called the expansion chamber, where they expand and lose some of their heat and pressure. a set of baffles in They are then directed through which there are holes that quiet the en- gine noise and shuttle the gases and sound into a silencing FOUR-STROKE EXHAUST SYSTEMS chamber. There, the gases make their way through a pipe The exhaust gases on a four-stroke engine must be directed lencing with holes surrounded by steel wool or fiberglass. out of the cylinder as smoothly as possible. Any unneces- sary bends or restrictions in the system will slow the flow of exhaust out of the engine. We haust system back pressure. Back pressure chokes off flow of exhaust. If not all call restrictions in the ex- the of the exhaust gases can get out of the cylinder, the leftover exhaust contaminates the fresh intake air-fuel mixture trast, set and results in lower power. By con- an exhaust system of the correct size and shape can up flow conditions that actually pull or extract exhaust gases out of the cylinder, resulting in an increase of power. Motorcycle engineers, of course, well understand the need to design a smooth-flowing exhaust. However, they chamber further reduces noise The si- and cuts down or prevents sparks from exiting the pipe. Twin- and multiple-cylinder engines may direct the ex- haust out of the engine in separate exhaust systems. twin-cylinder engine shown system each for left its in Figure and right cylinders. More com- monly, the runners from the are joined to a common one muffler, as shown typically The 14-3 has a separate left- and right-side systems pipe called a collector and go out in Figure 14-4. Multiple cylinders feed two sets of runners into a collector and muffler on each side of the motorcycle (Figure 14-5). properly designed collector system can often up exhaust gases and create an extractor work to A speed effect. have a number of other things to consider, e.g., noise levels, space limitations, and ground clearance. These consid- erations sometimes TWO-STROKE EXHAUST SYSTEMS result in exhaust systems that are less than perfect. The basic parts of a four-stroke exhaust system are shown in Figure 14—1 The exhaust is attached to the cylinder head through a flange assembly. The exhaust gases . flow into the runner pipe, the curves, length, and diameter The exhaust flow on a two-stroke engine is extremely important to good engine performance. The usual practice is to use individual rather than collector-style exhaust sys- tems on two strokers. The parts of a two-stroke individual exhaust system are shown in Figure 14-6. The exhaust is 207 REDUCING CONE -LER JOINT ASSEMBLY Figure 14-1. Four-stroke exhaust system. (Yamaha Motor Corp. U.S.A.) EXHAUST FLOW (^^) ARROW MARKS EXPANSION CHAMBER SILENCER CHAMBER BAFFLES STEEL WOOL OR FIBER GLASS INDICATES GAS FLOW Figure 14-2. Sectional view (Honda Motor RIGHT SIDE SYSTEM 208 LEFT SIDE SYSTEM of a muffler. Co.. Ltd.) Figure 14-3. A twin with separate exhaust sytems. (Moto Guzzi) TWO-STROKE EXHAUST SYSTEMS 209 MUFFLERS LER RUNNERS RIGHT SIDE COLLECTOR Figure 14-5. Multiple-cylinder engines use a collector and muffler on each side. (Honda Motor Co.. Ltd.) EXHAUST HEAD PIPE STRINGER PIPE MUFFLER COLLECTOR FLANGE EXPANSION CHAMBER MUFFLER BAFFLES Figure 14-6. Parts of a two-stroke exhaust system. (Honda Motor Co.. Ltd.) SHORT LONG EXPANSION EXPANSION CHAMBER .CHAMBER RUNNER Figure 14—4. The exhaust is connected to a and to a muffler. (Honda Motor Co.. collector Ltd.) mounted to the cylinder by a flange. Exhaust gases move through a head pipe to an expansion chamber which is part of a muffler with the same basic baffles and steel wool or packing that was described for the four-stroke The exhaust gases then exit through a small pipe fiberglass engine. HIGH RPM POWER called the stinger. The expansion chamber two-stroke exhaust. chamber makes it When is the exhaust port first opens, the Figure BDC and during the approximate tire it period, easier for the fresh gases to be the drawn When expansion convergent cone stinger at the end. upward and closes the transfer chamber creates a back pressure the piston starts the Two from flowing out into the exhaust pipe. Under extreme for a very special may even push some of the fresh mixture which has spilled into the exhaust pipe back into the cylinder. The expansion chamber is designed as a cone or mega- phone which merges into a cylindrical area, followed by a tails off into a small-diameter The exact diameter and length of each different expansion Figure 14-7. Each it which part are very critical. against the exhaust port to keep the fresh induction mixture conditions, expansion chamber into the en- combustion chamber area. port, 14-7. Different-length chambers affect engine performance. (Yamaha Motor Corp U.S.A.) easier to release the initial high-pressure surge of hot, expanding gas. After the transfer ports open, makes LOW RPM POWER the most important part of the is chamber designs specifically designed are shown in and constructed and limited application. The more help- more narrow is power band. For the higher rpm band, a shorter expansion chamber is used (Figure 14-7, left). Conversely, for the lower rpm range, the expansion chamber should be ful they are for a special use, however, the their as long as possible (Figure 14-7, right). 210 UNIT 14: Exhaust Systems and Turbocharging The component used called a turbocharger . to force air into the cylinder which is essentially an air is pump that raises or boosts the air pressure entering the cylinders. Increased air pressure from a turbocharger is called boost pressure. Figure 14—9 shows a turbocharger set within the whole system. There are a number of advantages to turbocharging. The main ones • are: Engine power output can be increased without increasing engine speed or displacement. Figure 14-8. Two-stroke exhausts must be routed for maximum ground • clearance. (U.S. • Suzuki Motor Corp.) Engine weight per horsepower can be reduced. Fuel efficiency to Because of the need for high ground clearance, most dirt two strokers loop the exhaust and run the stinger up beside the seat, as shown in Figure 14—8. This arrangement is • is increased by utilizing exhaust energy improve performance. Fuel economy can be increased through same applications. the use of smaller engines for the a Engine exhaust noise lowered. compromise between power and ground clearance. • TURBOCHARGING Turbocharger operation During a four-stroke engine's exhaust stroke, exhaust The gases leave the cylinder under high temperature and pres- 14-10. Exhaust gases from the cylinder are routed into the sure. There charging is is a is basics of turbocharger operation are shown in Figure a great deal of energy in these gases. Turbo- exhaust manifold, where a wheel with blades, called a tur- method of using bine, the energy in the exhaust gases to force air into the engine's cylinders. is mounted on a shaft supported by bearings. As the gases hit the blades of the turbine wheel, the wheel TURBOCHARGER Figure 14-9. A turbocharger uses exhaust gas energy gine's cylinders. (Honda Motor Co., Ltd.) to force air into the en- is TURBOCHARGING 211 COMPRESSOR TURBINE EXHAUST GAS i INTAKE AIR INTAKE AIR COMPRESSOR IMPELLER Figure 14-10. Operation (Honda Motor of a turbocharger. Co., Ltd.) ENGINE The gases then flow through an outlet The shaft that supports the turbine wheel forced to turn. into the exhaust. also Figure 14-11. The turbine drives the compressor, which raises the pressure of intake supports the turbocharger compressor impeller. This section of the turbocharger pump. Air ated by the pumped works any centrifugal just like rotating impeller blades. It is (Honda Motor air. pulled into the inlet by the low pressure cre- is Co., Ltd.) then compressed, out of the housing under pressure, and directed into the engine's cylinders. the In about is unturbocharged or naturally aspirated engine, 40% of the energy generated from fuel combustion discharged into the atmosphere as heat in the exhaust A gases. turbocharger uses a portion of the turbine same shaft. this energy to drive and the compressor, which are attached The compressor increases to the the pressure of the engine intake air (Figure 14-11) and enables the engine to effectively use a greater mixture of air is an increase in power output over and fuel. The result the naturally aspirated engine. The power increase resulting from the installation of a turbocharger varies with different engines and turbochargers. The brake horsepower of an engine can typically be increased by approximately 35 to 60 percent over the Figure 14-12. The (Ford Motor Co.) same compressor housing. displacement for a naturally aspirated engine. This increase is largely due to (1) more complete scavenging of exhaust amount of air to more dependent on engine load than on en- gases and (2) the presence of a greater the turbine support complete combustion. Air forced into the cylinder gine speed. Thus, scavenge or push out burned gases from the Since the turbocharger is operated off waste also helps to cylinder. no appreciable loss of horsepower, in cona supercharger that is mechanically driven by the gases, there trast to but its load is is if the engine's speed remains constant, increased, the speed of the turbocharger will increase, and so will delivery of air to the engine. is Turbocharger components engine. Operation of the turbocharger is dependent on the tem- The main parts of a turbocharger are a compressor hous- perature and flow of exhaust gases. The speed of the turbine will increase as the load on the engine (how hard the wheel, center housing, and wastegate. The compressor working) increases. In other words, the speed of housing (Figure 14—12) contains the compressor impeller engine is ing, compressor impeller wheel, turbine housing, turbine UNIT 212 14: Exhaust Systems and Turbocharging 14-13. The compressor wheel. (Ford Motor Co.) Figure Figure 14-15. The turbine wheel. (Ford Mo- impeller tor Co.) TURBINE SEAL Figure 14-14. The Motor Co.) wheel and is turbirie housing. (Ford used to diffuse and compress the flow of into the intake manifold. (Figure 14-13) draws air into the housing and directs flow. The impeller is made of an aluminum alloy so that its it 14-15) gases. Since the turbine driven by these exhaust at around 1,650° F made of special heat-resis- kept hot is (900° C) by exhaust gases, is it is The center housing (Figure 14-16) contains oil (Ford and oil seal. These seals prevent exhaust gases from entering the center housing and also prevent from entering the turbine housing or the compressor air wheel to the impeller the turbine wheel, its is wheel. rotation used to connect the turbine As is the exhaust gases power directed to the impeller by the center shaft. Lubricating oil enters through an oil passage at the top of the center housing and into the crankcase (Figure is returned through the bottom 14—17). The full-floating and thrust bearings are lubricated as the oil flows through. tant steel. and the and the compressor housing. The center shaft air. The turbine housing (Figure 14-14) contains the turbine wheel. It receives the exhaust gases and directs the flow onto the turbine wheel and into the exhaust system. The turbine wheel (Figure COMPRESSOR SEAL air The compressor impeller wheel can be quickly cooled by incoming SHAFT Figure 14-16. The center housing. Motor Co.) the shaft passages that are required to lubricate the bear- ings that the shaft rides on. It also contains the turbine seal The center shaft is supported on full-floating-type bear- ings (Figure 14—18) that are allowed to rotate not only the shaft but also in their housings. Lubrication is on provided TURBOCHARGING 213 OIL FLOATING BEARINGS SHAFT CENTER HOUSING Figure 14-17. Oil Co , Ltd.) on both sides of the bearings. This design results life CENTER SHAFT flow through the center housing. (Honda Motor bearing CENTER HOUSING in longer and reduced noise and vibration. Figure 14-18. The center shaft by floating bearings. (Honda supported Motor Co., is Ltd.) Turbocharger control The turbocharger develops a boost pressure that related to turbine and impeller speed. The faster directly is COMPRESSOR IMPELLER the turbo- charger shaft rotates, the higher the boost pressure into the engine. A control system to prevent the turbine pressures. Too high must be used on the turbocharger from overspeeding and BOOST PRESSURE PRESSURE CHAMBER to limit boost a boost pressure could cause engine damage. Motorcycle turbocharger speed and pressure control are achieved with an exhaust bypass path, system. which bypasses the exhaust turbine, the exhaust gases. A controls the flow. The wastegate valve is An alternate provided for valve in the bypass called a waste gate is EXHAUST GASES WASTEGATE a simple poppet- DIAPHRAGM style valve. and operation of a wastegate are shown in Figure 14—19. The wastegate consists of a diaphragm mounted The in a A parts housing and connected to the stem of a poppet valve. going part of the boost pressure to the engine is rotated through a pressure channel to the wastegate diaphragm. long as the boost pressure is As BOOST PRESSURE within the safe range, the dia- phragm holds the poppet valve all WASTE-GATE CLOSED POPPET VALVE (CLOSED in the closed position and the exhaust gases leaving the engine strike the turbine. When level, the the boost pressure rises to the predetermined diaphragm is stretched outward, so that on the stem of the poppet valve and opens valve open, some of a bypass channel it pushes With the the exhaust gases are routed through and do not strike the turbine. exhaust gas striking the turbine, the boost pressure. it. As it With less slows down, lowering the boost pressure is lowered, the diaphragm relaxes and the poppet valve closes again. Most motorcycle turbochargers are set to regulate a boost pressure of about 120 kPa (1.2 kg/cm'). POPPET VALVE (OPEN) WASTE-GATE OPEN BYPASS OPEN Figure 14-19. Parts and operation of the wastegate valve. (Honda Motor Co., Ltd.) 214 UNIT 14: Exhaust Systems and Turbocharging KEY TERMS component of a four-cycle exhaust which Collector: a brings together individual cylinder exhaust pipes into one pipe. Expansion chamber: a component of a four- and twostroke exhaust in which exhaust gases are allowed to expand. Muffler: a part of a four- and two-stroke exhaust that uses baffles and steel wool or fiberglass packing to reduce the noise of the exhaust. Turbocharger: an exhaust-driven air pump that is used to force air into the engine's cylinders. Wastegate: a poppet valve connected to a diaphragm that is used to bypass exhaust gases in order to control turbo- charger air output pressure. CHECKUP 1. Why is the smooth flow of exhaust important in a four-stroke exhaust? Identify the parts of the four-stroke exhaust their names in the spaces provided. by writing DISCUSSION TOPICS AND ACTIVITIES Identify the parts of a muffler by writing their names 215 in the spaces provided. 9. 10. Identify the parts of a two-stroke exhaust names in the spaces provided. by writing their 16. What 17. How 18. What is the purpose of the turbocharger turbine? 19. What is the purpose of the turbocharger compressor? the purpose of the turbocharger? does the turbocharger use exhaust gases to drive a compressor? II. 12. 13. 14. is 20. Explain how a wastegate works to control turbo- charger boost pressure. 15. DISCUSSION TOPICS AND ACTIVITIES 1. Mount several two-stroke exhaust systems with dif- ferent expansion ride the bike, chamber lengths on and try to a bike. Test- determine the relationship between expansion chamber length and performance. 2. What do you think would happen to an engine with a turbocharger wastegate stuck open? Stuck closed? I he purpose of the and to the engine, amounts for The basic 1. mix to efficient check and from forming A at the shown in Figure two-stroker) is The vent prevents 1 5- stored in- from the tank by gravity when a which would prevent bottom of the tank from the fuel fuel vented fuel tank cap allows the rider in the tank the flow of fuel enough to deliver the fuel in the cylinder. oil in a the tank. fill fuel flows valve to store the fuel with air in the proper burning Fuel (and sometimes The is parts of a fuel system are side the fuel tank. to system fiiel hundred miles of operation, for several vacuum fuel flow. to a fuel shut-off that allows the rider to stop the engine is off. A fuel tank to the carburetor, fuel with air in the correct proportion fuel line directs FUEL SYSTEM OPERATION which mixes the and then directs it to the crankcase (in a two-stroker) or the intake valve (in a four-stroker). and filters retor is An air filter attached to the carburetor cleans the air before it The carbu- enters the engine. controlled by a twist-grip hand throttle located on the right handlebar and connected throttle cable. In this unit, we to the carburetor describe how by a the fuel system operates. JOB COMPETENCY OBJECTIVES When you be able finish reading and studying this unit, you should to: 1 Describe the purpose of the basic components of a fuel 2. Explain the fundamentals of atomization, vaporiza- system. tion, 3. and mixture ratios. Identify the parts and explain the function of a basic carburetor. 4. Explain the operation of the slide throttle valve, carburetor's float, 5. main pilot, and starter metering systems. Describe the parts and operation of a constant- velocity carburetor. CARBURETOR FUNDAMENTALS As previously mentioned, air in the the carburetor mixes fuel with proper proportions to bum buretors have developed into fairly all inside the engine. Car- complex devices. They have similar parts, however, and operate on the same basic principles. The two basic things a carburetor does are atomize the fuel and meter the fuel into the the engine. air flowing into These jobs are carried out by the carburetor au- tomatically over a wide range of operating conditions, such as changing engine speeds, loads, and operating tempera- Gasoline in its Before gasoline can be used as fuel for an engine, i.e., can be mixed with broken into air to fine particles so that form a mixture that will it it bum. of the fuel liquid state does not oline vapor will Vaporization bum system. readily; only gas- bum. is the transformation of a substance from a Such a transformation occurs only when soaks up enough heat to boil. In a teakettle, liquid to a gas. the liquid water becomes water vapor or steam when heat ferred to the water, raising tures. must be atomized, Figure 15-1. Basic parts (Honda Motor Co., Ltd.) its temperature until reaches the boiling point. At this time In a carburetor, gasoline is stream as a spray. The spray drawn is it is it transfinally changes to steam. into the incoming air then atomized, or torn into 217 UNIT 218 engine is is a hollow tube or barrel an airstream to enter and pass through to the cylinder. The atmospheric pressure, the boiling far less than lowered a great deal. At is duced pressure, heat from the this re- correct mixture or ratio of fuel and air for efficient burning. we analyze is also needed the amount of hydrogen and carbon in amount of oxygen in the air, we would find that it takes just about 15 grams of air to completely bum 1 gram of gasoline. This can be called an air-fuel ratio of 15 to 1. With more fuel, we would have a richer the gasoline, and the in the air upon weight, not volume, because the volume of and fuel changes with pressure and temperature, while the weight of the mixture The air-fuel air is not affected by either. must be adjusted ratio meet the to load and speed. The bum mixing ratio, ratio of 15 to and is, is 1 for a fraction of the time that the engine an ideal or only achieved in reality, is running. to the problem of incomplete vaporization of the low speeds and the requirement of additional fuel speeds, the actual operational air-fuel ratio than 15 to is Due retor barrel stream of the engine operating, vacuum is also When speed increases and is the vac- its its center called flows through the ven- air pressure decreases. If the placed near a fuel nozzle, the nozzle works as As an atomizer. pressure fill a continuous is barrel has a restriction in a venturi (Figure 15-2). turi, its there through the barrel. air The carburetor falls. the stream of air flows past the nozzle, But when pressure reduced is its at the venturi, atmospheric pressure in the carburetor fuel bowl forces the fuel through the nozzle and into the airstream. Conse- quently, the fuel atomizes or mists in the airstream. Vaporization The barrel also aided is by the reduced pressure. size of the venturi is opening in our basic carburetor controlled by a piston-type throttle valve or slide The 15-3). (Figure 1. in the crankcase). Since time, the atmospheric pressure. Thus, the pressure at is uum. With high often richer at this difference forces the air through the barrel to fuel at at (or, in the two-stroker, the pis- vacuum creating a pis- vacuum the carburetor barrel. But the air outside the carbu- felt in venturi changing needs of the engine for particular conditions of theoretical their intake strokes, creating a combustion chamber moves up, ton mixture, with less fuel, a leaner mixture. Air-fuel ratios are based airstream in the this engine causes the airstream. The in the move down on the intake valves are open conditions. all vaporized and mixed into is A vacuum tons The carburetor meters or mixes proper air-fuel ratio for fuel barrel. surrounding air particles each drop of fuel causes the gasoline to vaporize. If the engine to permit form a mist, and the resulting air-fuel into the engine. Since the pressure in the point of the gasoline A mounted on to drawn fine droplets, mixture System Operation 15: Fuel rider's hand throttle control con- is nected through a throttle cable to the piston-type throttle A BASIC CARBURETOR valve or slide. When the rider twists the throttle open, the moves up out of the barrel, leaving the venturi size larger, so that more air can enter the engine. A strong vacuum is created just above the fuel nozzle, and if we add more fuel, the engine will mn faster. throttle valve In order to understand how a carburetor operates, let us build a basic carburetor (Figure 15-2). We can begin with In order to regulate the flow of fuel into the venturi, a tapered jet needle ( LOW VELOCITY LOW VELOCITY A / HIGH PRESSURE HIGH PRESSURE the throttle valve jet needle is is attached to the throttle valve. is lifted positioned in the nozzle. can then get around the The engine mns (Figure 15^). OPEN When tle < CLOSE valve fast jet into the engine. A great deal of fuel needle and into the on the large mixture of the rider twists the moves back air stream. air and hand control closed, the into the barrel At the same time, and less air VENTURI FUEL NOZZLE FUEL BOWL Figure 15-2. Basic parts of a carburetor. (Top: Kawasaki Motors Corp. U.S.A. Bottom: U.S. Suzuki Motor Corp.) Figure 15-3. The piston-type controls Corp.) venturi size. (U.S. throt- a larger part of the ta- ENGINE VACUUM BARRE fuel can get FUEL SPRAY ATMOSPHERIC PRESSURE When up, the small part of the tapered throttle Suzuki valve Motor CARBURETOR METERING SYSTEMS 219 THROTTLE CABLE NOZZLE (NEEDLE JET) THROTTLE VALVE • m^//////////////^ 14 TO 1 AIR/FUEL MIXTURE AIR FLOWING ilN MAIN BORE E -^ NOZZLE (NEEDLE JET) FUEL BOWL NEEDLE VALVE SEAT FLOAT NEEDLE VALVE MAIN JET Figure 15-4. The and throttle valve controls air PIVOT fuel flow. GROOVES OPEN THROTTLE CLOSED THROTTLE FLOAT ARM FLOAT (6 FLOAT CHAMBER IN TOTAL) Figure 15-6. The DETAIL OF JET tem NEEDLE for low-speed running, CLEARANCE BETWEEN NEEDLE JET (NOZZLE) AND JET NEEDLE Figure 15-5. The tapered The CLIP needle opens and closes the nozzle. (U.S. Suzuki Motor jet Corp) is positioned in the nozzle (Figure 15-5), allowing less fuel to get through the nozzle and into the venturi. With bowl or chamber (Figure 15-6) float is less air and fuel, the engine slows down. CARBURETOR METERING SYSTEMS system to assist systems that meter the upper portion of the chamber cavity is the source of fuel. The float The vented to the atmo- sphere, so that the air pressure inside the as that outside the bowl. trap in the is attached to the bottom of the carburetor. find their way bowl Some models have bottom of the bowl which might pered jet needle starter discussion of these systems system chamber JET NEEDLE and the A cold engine. fuel for the other AND fuel their operation follows. Float LARGE -OPENING (•) FOR FUEL OPENING FOR FUEL bowel provides all in starting a and SMALL float the carburetor systems. (U.S. Suzuki Motor Corp.) to to catch into the fuel. is the same a sediment any solid particles The sediment trap prevents the solid particles from reaching the carburetor. in the float bowl is controlled by a float (or and a needle valve. The lower end of the needle valve rides on the float arm or tang, and the upper end Fuel level floats) seals against the needle valve seat. When the level of the bowl drops, the float drops slightly and the needle valve moves down, away from the seat (Figure 15-7). fuel in the All piston-type throttle valve carburetors have the sic parts just same ba- discussed. In addition, these carburetors have number of separate systems to supply fuel and air as required. The fuel supply is handled by the float bowl. Three a separate systems meter the fuel ing air: the main system and mix it with the incom- for normal running, the pilot sys- Fuel is then allowed to flow from the tank into the bowl. As more fuel enters the bowl, the float rises, pushing the needle valve back into contact with the valve seat and shutting off the flow of fuel (Figure 15-8). The float level is kept almost constant by this continual self-adjustment. 220 UNIT System Operation 15: Fuel THROTTLE VALVE OR SLIDE CUTAWAY NEEDLE VALVE SEAT JET NEEDLE AIR FLOW — MAIN NOZZLE '(NEEDLE JET) MAIN JET Figure 15-9. Parts of the (U.S. Suzuki Motor Corp.) NEEDLE VALVE When Figure 15-7. dle valve opens. U.S.A.) Figure 15-8. The the needle valve. the float drops, the nee- (Kawasaki Motors Corp. float moves up and closes (Kawasaki Motors Corp. U.S.A.) The main system Most of the metering performed by the carburetor by the main system whose components are the is done throttle valve or slide, jet needle, main nozzle, and main jet (Figure 15-9). venturi to As soon draw fuel as there up system begins to take effect. meter fuel from about '/s is enough air flow through the main The main system components throttle to full throttle. As previously mentioned, carburetor is into the nozzle assembly, the the determined by the amount of air entering the throttle valve (slide). The main system. CARBURETOR METERING SYSTEMS tapered itself is grooves at its The top of at its lower end and has (usually five) upper end. (Refer back to Figure 15-5.) the needle is fastened to the throttle valve, and the tapered end extends into the needle The needle nozzle. 221 jet fits jet or main in the carburetor body in the SMALL CLEARANCE MEDIUM CLEARANCE LARGE CLEARANCE L center of the venturi. The lower end of the nozzle gets fuel chamber. Since the inside diameter of the from the float nozzle just fractionally greater than the nontapered sec- is J tion of the needle, the needle effectively blocks the jet when the throttle valve needle is is all lifted, the closed (Figure 15-11) and the is way down the needle rises in the nozzle. to gradually n L the valve up out of the nozzle, allowing fuel to flow past the tapered section. is When ci The effect of the taper and progressively increase the clearance be- tween the nozzle and the jet needle as the needle is lifted. The varying amounts of clearance at different throttle positions are shown in Figure 15-12. As the valve and needle are raised, air valve creates a low pressure in the venturi. the float bowl is drawn by flow under the The the reduced pressure fuel up from into the nozzle and through the clearance area between the nozzle VERY SMALL CLEARANCE Figure 15-12. As the throttle valve or slide and jet needle are lifted, the opening around the jet needle allows for an increase in fuel flow. (Kawasaki Motors Corp. U.S.A.) JET NEEDLE GROOVES OVERALL LENGTH FIRST TAPER NOZZLE OR NEEDLE JET SECOND TAPER Figure 15-13. Double-tapered jet needle used in some larger two-strokers. (Kawasaki Motors Corp. U.S.A.) and the needle. The greater the clearance as the needle is lifted, the greater is the amount of fuel that can be drawn up into the venturi. Four-stroke engines and small-displacement two-stroke Figure 15-11. When the throttle slide is lowered, the jet needle closes off the nozzle or needle jet. (Kawasaki Motors Corp. U.S.A.) engines often use a needle with a single taper. Many larger two-stroke engines use a needle with two tapered areas called a double taper (Figure 15-13). of the The double ta- per of the needle helps accelerate the low rate of fuel intake so that the amount of fuel can keep up with the in- UNIT 222 creasing 15: Fuel amount of System Operation air in the higher throttle positions, thus resulting in a richer mixture at high speeds. The needle that fits into is attached to the valve or slide with a clip one of the grooves (Figure 15-5). The at the PRIMARY CHOKE top of the needle main system air-fuel mixture for the can be adjusted by selecting a different groove to attach the AIR needle to the valve by the clip. Since the position of the NOZZLE ASSEMBLY needle relative to the nozzle determines the amount of fuel on the valve available, changing the position of the needle changes the amount of fuel needle sits let in. If lower and the fuel flow in a leaner mixture. If the clip is up and the the clip goes up, the is MAIN JET restricted, resulting lowered, the needle goes fuel flow is increased, resulting in a richer mix- Figure 15-15. Primary-type nozzle assembly. {U.S. Suzuki Motor Corp.) ture. The nozzle also into the venturi. works to atomize the fuel before Atomization of the fuel it gets accomplished is by one of two types of nozzles: the primary type and the air bleed type. The primary type tends to allow more fuel to flow, producing richer mixtures, and is used mostly on larger two-stroke engines. Four-stroke engines and smaller two-strokers usually use the bleed type. The air around its bleed type of nozzle (Figure 15-14) has holes circumference where some of the front of the carburetor the main nozzle. air from the Figure 15-16. Fuel passes introduced into the fuel going up is In the air bleed design, air the fuel before the fuel exits past the needle. mixed with The atomized is jet. a reservoir nozzle Suzuki Motor into the (U.S. Corp.) fuel as they leave the center air-fuel mixture flows readily past the needle. The primary-type nozzle (Figure 15-15) has mam the throughi metering portion of the nozzle assembly. A lip extends up into the venturi This lip generates turbulence, which creates a greater vac- buretor body to a very small air jet in the front (away from uum behind the the engine) end of the carburetor. Air flows into this jet, which surrounds the point needle. This reservoir is at which the fuel exits past the connected by passages in the car- lip in front of the needle. where the reservoir and needle are lo- flow is vacuum effect helps pull more fuel up from the float bowl. The lip on the nozzle is known as a primary choke. The height of the primary choke determines the amount of turbulence and, consequently, the amount of extra vacuum at the venturi exit of aided (by the pressure differential). The size of the jet is the needle jet. through the passages, mixes with the fuel and and into the reservoir, where is entrance to this passage and the is at near atmospheric pressure, vacuum, air arrives at the reservoir at At the reservoir, the it into the venturi. Since the exit is subject to the venturi very small, so the locity. drawn air helps air a high ve- break up the drops of cated. At high rpm, lence and A this extra taller primary choke creates more turbu- more suction acting on richment of the mixture at the fuel, leading to en- high rpm. Use of a mary choke allows a smaller main jet approximately the same mixture ratio to be used taller pri- to achieve at full throttle. How- ever, a decrease in fuel consumption results in the medi- um-throttle positions. Fuel flows into the fuel nozzle from the float chamber AIR. through a calibrated hole called a main jet (Figure 15-16). AIR BLEED NOZZLE AIR ASSEMBLY — MAIN JET The main jet screws into the bottom of the nozzle, as shown in Figure 15-15. As soon as the main system begins to meter fuel, the throttle valve cutaway, needle, and main jet work together to determine the amount of fuel that should be delivered for the amount of air entering the engine. This working relationship Figure 15-14. An air-bleed nozzle asembly. (U.S. Suzuki Motor Corp.) throttle. continues until approximately At somewhere around tional area of the clearance three-fourths this point, the cross-sec- between the jet needle and the CARBURETOR METERING SYSTEMS nozzle becomes greater than the cross-sectional area of the main jet, resulting in the size of the main no further how much ^ and fuel flow restrictions, then determines jet # fuel will be available. The of the main jet size stamped on the jets, is There are three different jet. each with a different numbering system. be careful, when changing main same of the AIR FLOW] number types of main indicated by the "~A VENTURI THROTTLE VALVE (SLIDE) LOW PRESSURE MIXTURE should use a replacement jets, to type; matching only the You HIGH PRESSURE numbers can result in PILOT OUTLET PILOT BYPASS an engine that will not run properly. Pilot or When low-speed system the rider is operating the motorcycle speed and small throttle opening, it is low engine at a impossible for the main system to provide the proper amount of fuel or air. The reason is because at a low speed and small throttle opening the flow through the venturi air produce enough venturi vacuum to float lift is Figure 15-18. Operation of the pilot system. (Kawasaki Motors Corp. U.S.A.) insufficient to the fuel up from the slow engine operation. The parts of the system are a series of passageways pilot body, a meter pilot jet to ter air (Figure 15-17). The air for the pilot carburetor and is in air fuel, and a is in the pilot air carburetor screw to me- flow as the screw pilot air screw (Figure is backed out. The taper fits all in the the way passageway off completely. The fuel for the pilot mixture is drawn through the pilot jet, which sticks into the float chamber, usually just behind in closes the body at the the air before it enters the venturi through the pilot outlet, which has a very small diameter (Figure 15-18). The and fuel are blended into an atomized mixture. Starter or choke system pilot jet has a series of holes drilled point where the air is When the engine is cold, enough to Under such circumstances, parts are not hot its vaporize the droplets of fuel. an even richer mixture than that provided by the pilot sys- tem is required to start To the engine. generate these richer mixtures, a starter system or choke system is As shown introduced from the air PILOT AIR SCREW to the in Figure 15-19, the starter system consists of which opens passages from the front of the carburetor into the ven- The plunger is lifted by a cable or lever that is usually mounted on or near the accelerator twist-grip on the han- turi. ±1 W added carburetor. a starter jet to meter the fuel and a plunger AIRFLOW air tapered to provide a gradual increase center of a passageway, and turning the screw main system. The passageways. These holes allow the fuel to be mixed with system enters from the front of the metered by the 15-17). This screw in its PILOT JET bowl. The pilot or low-speed system provides the air- fuel mixture for the 223 dlebar. THROTTLE VALVE (SLIDE) As the plunger lifts off its seal, it passageway. Lifting the plunger further VENTURI the air inlet passage PILOT BYPASS PILOT OUTLET on the engine side of the is closed (as that goes it to the and the outlet uncovers the fuel starts to to the venturi, uncover which is throttle slide. If the throttle slide should be for starting), almost engine must come through all the air the starter pas- When it does, enough suction is created to draw up from the bowl into the chamber below the plunger, where the fuel is mixed with air from the front of the carburetor and drawn into the venturi and the engine. sageways. fuel The process of atomization of fuel for starting by the emulsion tube, a long tube which PILOT JET Figure 15-17. Parts of the pilot system. (Kawasaki Motors Corp. U.S.A.) is aided sticks into the fuel and through which the fuel from the starter jet is drawn. This tube has holes drilled in it which allow a small amount of air from the fuel before it enters the chamber to be mixed with the chamber below the starter plunger. float UNIT 224 15: Fuel System Operation STARTER CABLE OPEN BUTTERFLY-TYPE^ THROTTLE VALVE FULLY CLOSED THROTTLE VALVE SHAFT OPEN CLOSE Figure 15-20. Butterfly valve carburetor. velocity THROTTLE VALVE (SLIDE) ENGINE SIDE Main system operation parts of a constant-velocity carburetor system are shown piston or slide main metering Figure 15-21. The vacuum-operated is lifted by the engine vacuum. is A flexible attached to the piston top and housing divides the top part of the carburetor into a vac- PASSAGE FOR STARTING uum chamber above pressure EMULSION TUBE IR CLEANER SIDE JET STARTER GASOLINE air the diaphragm. passes through the atmospheric pressure chamber and occupies the space below the diaphragm. A at the bottom of the vacuum piston provides an unobstructed path for air to flow up into the vacuum chamber. As air is pulled past the bottom of the vacuum piston by the engine vacuum, a low-pressure area is created at the bottom of the piston. The piston hole permits this low hole drilled pressure to Figure 15-19. The starter system provides a rich mixture for cold starts. (Honda Motor sures Co.. Ltd.) result of the four-stroke carburetors use a choke either along the diaphragm, and an atmospheric chamber below Atmospheric Some in rubber diaphragm that COMMON in a constantSuzuki Motor Corp.) The STARTER PLUNGER (U.S. on fill the vacuum chamber, the two sides of the unequal so that the air pres- diaphragm are unequal. As a air pressures, pushes up on the diaphragm, atmospheric pressure lifting the vacuum piston. with or in place of the starter system. The choke consists The diaphragm and of a round butterfly valve mounted on a shaft in the barrel produced by the force of the vacuum piston return spring in front of the throttle valve. a cable or lever, it reduces air When the valve is closed by flow through the carburetor, which causes an increase in vacuum within the venturi, which in turn pulls in extra fuel from the pilot and main systems. start the The extra fuel causes a rich enough mixture to cold engine. air pressure lift until the pressure match the pushing atmospheric pressure below. Air speed through the venturi, which controls the amount of low pressure in the vacuum chamber, is controlled by a butterfly valve (Figure 15-21) to which the throttle grip is directly connected by a cable. Twisting the grip opens the valve. CONSTANT-VELOCITY CARBURETORS A and the low piston continue to the engine vacuum As the valve opens (Figure 15-22), pulls air through the venturi at a greater speed, which causes a greater drop in air pressure. The number of the larger street motorcycles use a set of con- stant-velocity carburetors (one for each cylinder). The con- lower pressure immediately occupies the vacuum chamber, lifting the stant-velocity carburetor has the accelerator twist-grip con- to nected to a round butterfly valve that piston is in turn attached to a shaft on the engine side of the venturi (Figure 15-20). It also has a throttle slide and a jet needle, but they are free floating, and not connected The purpose of lift vacuum piston higher. as the butterfly is lifts, it fuel to flow also lifts up the opened The piston further. will continue When the vacuum the jet needle, permitting additional fuel outlet nozzle or needle jet to the engine (in the standard method of use). to the accelerator twist-grip. a constant-velocity carburetor is to main- Pilot or idle circuit tain a constant air velocity through the venturi regardless of the amount of throttle opening. This prevents any engine hesitation when the rider snaps open the throttle. Like other carburetors, the constant-velocity carburetor requires a float system, a starter system, and a pilot or idle CARBURETOR VACUUM CHAMBER SIZE 225 ETURN SPRING ATMOSPHERIC PRESSURE CHAMBER DIAPHRAGM Tr-i ATMOSPHERIC [ PRESSURE (Z[> CHAMBER VACUUM OPERATED PISTON (SLIDE) BUTTERFLY VALVE VACUUM CHAMBER JET NEEDLE PISTON ORIFICE NOZZLE FLOAT CHAMBER Figure 15-21. Constant-velocity carburetor. (Yamaha Motor Corp. U.S.A.) To system. The float and starter systems are the same as those previously described (see Figures 15-6 and 15-19). The idle or carburetor is slow-speed system for a constant-velocity shown in Figure 15-23. The idle speed increase engine rpm, the butterfly valve further (Figure 15-24). is covers more first one bypass The top edge of outlet, is opened the butterfly un- and then another, permitting fuel to progressively enter the venturi and to mix controlled by the position of the butterfly valve. At idling with the additional air that begins to flow past the partially rpm, opened fuel the pilot outlet. els air pressure in the venturi is not low enough to draw up through the needle jet or main nozzle. So fuel travup through the main jet to the pilot jet. At the same time, air passes through the pilot air jet drilled passage to the pilot jet, fuel. The air-fuel mixture passes sage to the pilot outlet in front at where down through it a is up through a drilled pas- the upper edge of the venturi, just controlled by the pilot screw. CARBURETOR still flows out of SIZE mixes with the of the butterfly. The amount of the mixture sent to the engine butterfly valve. In addition, fuel Regardless of what type they are, carburetors are classified by size (diameter) of their venturi (Figure venturi of the carburetor regulates the air drawn 15-25). The maximum amount of into the engine, so a carburetor with a large- 226 UNIT 15: Fuel System Operation AIR INTAKE The engine pulls in a tremendous amount of carburetor. To dust and dirt out before filter engine, the air it enters the routed through an intake box or case is which houses an through the air air cleaner. This large housing located is next to the carburetor assembly (Figure 15-26). Inside the housing is a paper or polyurethane whose openings are but small enough to large enough trap dirt foam filter element to let air pass through, and dust (Figure 15-27). KEY TERMS AIR Air intake: a large filter assembly mounted above the car- buretor to clean the air before it enters the engine. Atomization: breaking a liquid fuel into small droplets to aid in vaporizing the fuel. Carburetor: part of the fuel system that mixes in the correct Float system: amounts a to bum carburetor air and fuel in the engine. system that uses a float- controlled needle valve in a barrel to provide the correct amount of Main system: Figure 15-22. Operation velocity carburetor is when fuel for all the other circuits. a carburetor system that uses a piston or slide the constant- to control the position of a needle in a fuel nozzle to the butterfly valve provide the necessary air-fuel mixture for most operat- of opened. (Yamaha Motor Corp. USA.) ing conditions. Pilot system: a carburetor system that provides the air-fuel mixture that is required for slow- or low-speed engine operation. diameter venturi is necessary for large-capacity and high- speed engines. However, maximum output gets worse, is if the venturi is too high, the response and the fuel practice is consumption at so large that at low speeds these speeds is very poor. The usual to install a carburetor for vidual cylinder of the engine. each indi- Starter system: a carburetor system that provides the airfuel mixture that is required for starting a cold engine. Venturi: a restricted area in the carburetor barrel that is used to develop low pressure to pull in fuel from the nozzle. Vaporization: turning liquid gasoline into a gas or vapor. PILOT SCREW PILOT OUTLET PILOT AIR JET C^ BUTTERFLY VALVE Figure 15-23. Idle system components. (Yamaha Motor Corp^ U.S.A.) BYPASS OUTLET Figure 15-24. Air and fuel flow out the bypass passages. (Yamaha Motor Corp. U.S.A.) VENTURI BUTTERFLY VALVE '^ 1 (mm) Figure 15-25. Carburetors are classified by Motor Corp.) venturi size. (U.S. Suzuki 227 AIR CLEANER Figure 15-26. The to the air intake box attached carburetors houses the (Honda Motor air cleaner. Co., Ltd.) Figure 15-27. The air cleaner element traps before it can enter the engine. (Mikuni dirt American Corp.) 228 CHECKUP CHECKUP Identify the basic parts of a fuel system by writing their names in the spaces provided. Identify the basic parts of a carburetor by writing their names 9. 10. 11. 12. in the spaces provided. 229 230 UNIT 15: Fuel System Operation Identify the parts of the carburetor in the spaces provided. 13. 14. 15. 16. 17. 18. 19. 20. by writing their names DISCUSSION TOPICS AND ACTIVITIES Identify the parts of the constant-velocity carburetor writing their names in the spaces provided. by DISCUSSION TOPICS AND ACTIVITIES 1. 21. 24. Use a cutaway piston slide throttle valve carburetor and identify the float, main, pilot, and starter to trace systems. 22. 23. 231 2. Use a cutaway constant-velocity carburetor and identify the float, main, pilot, tems. 25. 26. 27. 28. 29. 30. ***^ — ., y) and to trace starter sys- f^ motorcycle engine must have the correct air-fuel mixthe engine hard to or too problem may make fuel or not even start start at all. Too much The fuel will cause the engine to run roughly. little problem can be as simple as change of A and run smoothly. ture to start air filter. retor overhaul. In this a carburetor adjustment or a may unit, we Or it require a complete carbu- describe the troubleshoot- ing and servicing procedures used on the fuel system. JOB COMPETENCY OBJECTIVES When you be able finish reading this unit, you should to: how Describe 1. and studying to troubleshoot an it is running too rich or too lean. 2. Explain how to service an air filter. 3. Explain how to adjust the throttle Explain how to adjust the idle mixture, idle speed, and starter cables. and main mixture. how TROUBLESHOOTING AND SERVICING engine to determine whether 4. FUEL SYSTEM fuel lines, an air cleaner, a twist grip, tion of the throttle 5. Describe to synchronize multiple carburetors. 6. Overhaul a carburetor. and and cables for opera- starter system. These If the mixture appears rich, check the entry of air FUEL SYSTEM TROUBLESHOOTING The first step in fuel system troubleshooting ture that is too rich enough too The is that is too lean to way to if the starter cable is too tight, the allowing extra fuel into the venturi. A mix- and color. Also, the spark plugs is a fuel the spark plugs. If the mix- light all is to determine determine whether there remove each of ture has the correct proportions of air should impaired; can have either end of each spark plug will have a not, there is plunger and the dirty, the or not enough fuel. air fastest problem starter is can have either too much fuel or not and a mixture air, much is too rich or too lean. is play their air cleaner cable to the starter system. If the air cleaner whether the air-fuel mixture all part in the proper functioning of the engine. fuel, the firing brown or tan on twin and multiple cylinders have the same color (Figure 16-1). If may (to be a synchronization problem they do be de- scribed later). If the air-fuel firing mixture Figure 16-2. This soot do not confuse If the is too rich, the fuel will cover the end of the spark plug with its is a black soot, as relatively dry shown and free of oil, presence with the presence of excess dark deposit on the plug is oily in so oil. and rubs off easily oil. Otherwise, if you find on its firing end, the problem is too much fuel or not enough air. On the other hand, if the spark plug end is dry and white in color (Figure 16-3), the problem is too lean a mixture: either the engine is not get- in your hand, it is not fuel, but a spark plug with fuel ting enough fuel, or it is getting too much After determining whether the mixture lean, examine some of the external carburetion. Remember, air. is too rich or too factors that can affect the fuel system consists of than just the carburetor. There is more also a fuel tank shutoff. Figure 16-1. The correct leaves a spark plug. air-fuel mixture brown color on the (Champion Spark Plug Co.) light tan or 233 UNIT 234 System Troubleshooting and Servicing 16: Fuel CARBURETOR ENGINE Figure 16-4. Air leaks between the carburetor and engine can cause a lean condition. Since most of the intake system at less is than atmo- spheric pressure, any leak will pull in air from outside the Figure means 16-2. A sooty black, spark intake, generating a lean mixture. For example, a leak can plug (Champion Spark too rich a mixture. form Plug Co.) its in the neoprene-type manifold from the cracking of rubber or the loosening of the nuts which hold in it pound place. Or, the constant vibration of the engine can the phenolic bushing that fits around the metal spigot in one type of carburetor-to-engine connection, pushing the bushing out of shape, and allowing air to leak in past it. Inspect these areas carefully, and tighten or replace any parts you find to be defective. You can often use duct tape to temporarily seal a suspected air leak performance is down when you affected. seal off a leak The operation of works the and see because it gets less air. the fuel system begins throttle twist grip. the accelerator cable engine if (The engine will usually slow when the rider Turning the twist grip winds around a drum, thereby exerting a pulling force at the throttle slide or butterfly valve. most frequent source of trouble which might fray as it in this system is The the cable, exits the twist-grip assembly. An- other potential source, particularly on a motorcycle that not ridden for a period of several weeks or months, A dry, white spark plug means a lean mixture. (Champion Spark Plug Co.) Figure 16-3. If the mixture is too lean, the disconnecting the fuel line grease that lubricates the twist-grip-handlebar area. Hard- problem might be a at the carburetor and momentar- turning the fuel shutoff valve to When "on" or "prime." these are done, there should be a strong flow of fuel to idle, and a generally sluggish new A coat of grease should cure this problem. fuel starvation When metal container and dispose of take the space left An air leak at the carburetor-to-engine connection (Fig- ure 16-4) can also cause too lean a mixture (too There are two basic types of connections: retor slips over a metal or Figure 16-5, or it case the carburetor much air). either the carbu- neoprene spigot, as shown slips into a commonly in neoprene socket. In either bolts to an intake pipe or di- rectly to the engine (Figure 16-6). problem can sometimes be traced plugged fuel tank vent. This vent cap. properly.) Simply feel to the throttle. cleaning the twist grip and the handlebar and applying a out of the fuel line. (Safety- Caution: Catch the fuel in a it is the ening of this grease causes high throttle effort, slow return clogged fuel shutoff valve. This can easily be checked by ily is it is plugged up, by is air the fuel as to a located in the fuel tank cannot enter the tank to it is used, and a vacuum The problem can be is sufficiently serious to slow the flow of fuel enough so that the engine dies while being ridden. If you suspect this created in the tank, above the fuel. problem, replace the fuel tank cap with a If your external checks time for a new one. uncover the problem, it is There are several possible symptoms mixture that may occur under riding condi- test ride. of a rich fuel fail to FUEL SYSTEM TROUBLESHOOTING 235 FUEL TANK CAP FUEL TANK Figure 16-5. Carburetor assembly: spigot or socket connection with clamp. (Honda Motor Co., Ltd.) tions. If the in a engine runs roughly and/or misses (a condition two-stroker result known as '"four-stroking"), it may be the of occasionally incomplete combustion caused by much fuel on the spark plugs. Look for exhaust smoke especially too — exhaust sometimes is determine, since most two-stroke motorcycles smoke anyway and most visible two-stroke exhaust is oil. Oil smoke, however, is blue or white in color. mostly If the worse as rich engine it when is warms running on too rich a mixture, up. the engine Remember is cold. that the As it will run mixture must be the engine warms up, warm continued feeding of a rich mixture will cause the engine to run poorly. cleaner is the engine runs better. if clean, it restricts the ture. If the fuel-air ratio is too rich to ing the air cleaner ture, making When from the system the engine run an engine is Even to the air if the air flow of air to the engine. Eliminating this restriction allows more black smoke, caused by an overrich mixture. This difficult to Try temporarily removing the connector tube cleaner to see much mix- will yield a leaner better. running on too lean a mixture, overheat. Overheating, however, mix- air into the begin with, remov- is sometimes it will difficult to determine. Engines with chrome exhaust pipes will show signs of severe blueing near the exhaust port. Also, some- times an engine that is overheating will smell strongly of hot metal. A lean mixture can cause the engine speed to fluctuate UNIT 236 16: Fuel System Troubleshooting and Servicing THROTTLE VALVE pilot outlet or bypass blocked fuel level too low bowl in float nozzle blocked deposits or dirt main jet on blocked jet needle - incorrect pilot air screw adjustment incorrect slide needle adjustment FUEL SYSTEM SERVICING Fuel system servicing CLAMP placing the air may be as simple as cleaning or re- element, setting the idle speed, syn- filter chronizing multiple carburetors, or adjusting cable play. Or Figure 16-6. Carburetor assembly: bolted to engine. (Honda Motor Co.. Ltd.) may be it as complicated as overhauling the carburetors completely. All of these procedures are explained in detail in the individual service manuals and owner handbooks. Specific settings for the needle position, air screw, and or "surge" at a constant throttle position, and the engine consequently lack power. will hard if You should not ride the bike you suspect a lean mixture; could overheat to the point that if you do, the engine Try pushing the starting or choke lever as you are riding. An engine that the starting lever mixture. Be is is running too lean will run better is first wanned up it the shop service manual is is a too rich a too lean mixture, you should check mixture, or that for a detailed fuel system trouble- shooting guide. The manual will provide a step-by-step and service adjustment procedure to cure a specific made to be to suit local conditions we describe some of the general procedures. Air filter servicing air filter must be cleaned or replaced regularly sure that only clean, filtered air enters the engine. filter element is located in a filter filter air container or box assem- bly attached to the carburetor intake (Figure some arrangements the to remove the filter. In to en- The 16-7). In container has to be removed others, a clip or screw is removed to gain access to the filter element. problem. Some some changes may have The have determined that the problem manuals and the to operating temperature. When you in the service if pushed because doing so richens up the sure the engine given or the habits of the rider. In this section could be damaged. it float level are also tuning charts. These settings are recommendations, and of the possible causes of a too rich mixture are: There are two styles of filter elements: foam and paper. you are servicing the foam type (Figure 16-8), wash the element gently, but thoroughly, in solvent. Squeeze the exIf needle main jet/jet needle worn primary air small quantity of passage blocked fuel level too high in float air let it dry. Then pour a lOW-30 SE motor oil onto the filter and throughly into the porous foam material. cess solvent out of the element and jet loose work it bowl cleaner clogged starter FILTER ELEMENT plunger not seated pilot jet air bleed blocked incorrect pilot air screw adjustment incorrect slide needle adjustment Some of the possible causes of a too lean mixture are: carburetor FILTER BOX OR CONTAINER mount loose throttle valve worn, allowing air to pass around valve Figure 16-7. The pilot jet blocked filter assembly is located (Yamaha Motor the filter container or box. Corp. U.S.A.) in FUEL SYSTEM SERVICING FOAM FILTER ELEMENT 237 Cable adjustments CASE Accelerator twist-grip adjustment affects carburetor perfor- mance. Always follow the specific adjustment procedure A the shop service manual. in throttle cable that is too tight will cause the engine to idle too fast because the throttle slide cannot return all the other hand, too sloppy feeling way the much to the closed position. On play in the cable results in a at the throttle grip and can very likely cause a decrease in performance because the throttle slides might not completely clear the venturi. An adjuster and lock nut on top of the carburetor allows the cable housing to be lengthened or shortened (Figure 16-9). Slide the rubber cover off the top of the carburetor and grasp the outer cable housing. slack, If the which should be about slack is 1 Lift up and it mm (.039") feel the at the adjuster. incorrect, loosen the locknut and turn the ad- justing nut in or out as required to achieve the correct CARBURETOR slack. Tighten the locknut Figure 16-8. Foam-type side the filter air filter box or case. located (U.S. Suzuki If the in- Mo- throttle valves are Corp.) tor and reinstall the operated by cable (not by a vacuum), you must make sure that each valve You by removing the amount. cap cover. motorcycle has more than one carburetor and the can tell is lifted the air filter same assembly and watching the valves while someone opens and closes In order to function properly, the damp with ping with oil at all times. It oil. foam element must be should not, however, be drip- Coat the upper and lower edges of the element with light grease, which will provide an between the stall the element assembly and replace the parts that have case cover and the filter seat. Rein- cleaner is enough play, the its seat, play is starter the dry-paper type, cleaned with any type of solvent. A it must not be important. also If there plunger will always be mixture at all throttle positions. 1 mm The (.039") of play. an adjuster, just like the throttle valve. dusty air cleaner can from the inside out. (Safety caution: Wear eye protection when using compressed air.) Use low pressure and hold from the element to avoid rupturing the element. If the contamination adheres to the filter cles, element, use a soft brush to dislodge the parti- and then blow the filter with air. An extremely dirty or oil-soaked element should be replaced. After cleaning, reinstall the air filter Each time check the assembly. element maintenance air inlet to the filter check the manifold filter an performed, case for obstructions. Also, air cleaner to the carburetor fittings for is airtight seal. rubber hose and Tighten thoroughly to avoid the possibility of unfiltered all ft)(n) fittings air entering Never operate the engine with the air filter element removed because doing so allows unfiltered air to enter. Dirt will then cause rapid wear and possible engine ~ 1.0 mm (0.02 ~ 0.04 in) 0.5 the engine. damage. Also, operating without the fect carburetor jetting filter element will af- and cause poor performance and possible engine overheating. is not lifted off be cleaned by blowing compressed air through the element the air nozzle at least three inches height allowing extra fuel to enter the venturi, which re- sults in a rich cable should also have about been removed for access. If the air Starter cable filter airtight seal filter The valves should each be at the same when viewed through the bore (Figure 16-10). the throttle. 1. LOCKNUT 2. ADJUSTER Figure 16-9. An adjusting nut for adjusting cable housing play. (U.S. Suzuki Mo- throttle tor Corp.) starter It has UNIT 238 System Troubleshooting and Servicing 16: Fuel NOZZLE (NEEDLE Figure 16-10. These are not the lifting throttle JET) valves (slides) same amount and must be adjusted. AIR FLOWING MAIN BORE IN 16-11. Figure Idle air adjusting NEEDLE VALVE SEAT FLOAT NEEDLE VALVE screw/. (Yamaha Motor Corp. U.S.A.) PIVOT FLOAT ARM FLOAT mixture and speed adjustments idle FLOAT CHAMBER One adjustment on and smoothness air of the carburetor that affects idle speed an is idle Figure 16-12. The idle mixture on this carburetor is adjusted w/ith a pilot air screw. (U.S. Suzuki Motor Corp.) mixture adjusting screw, or idle screw (Figure 16-11). This screw regulates the mixture and fuel that air tion and affects is available for idle or low-speed opera- how smooth the engine runs. Different carburetors use different types of mixture ad- Most justments. screw (Figure AIR variable- venturi carburetors use a pilot air 16-12) that threads housing. The end of the screw pilot air passage. When is tapered and the screw carburetor to the in fits into the turned inwards, the is tapered end closes off the air flow and changes the idle A mixture. spring on the screw holds regulates an air-fuel mixture which closed throttle butterfly valve (Figure 16-13). screw creased; is When turned inwards, the amount of mixture is when is To zle (Figure 16-14). valve adjust either type of screw, first get the engine starter cable is not is warm pushed. Allow the pered end can be damaged.) Finally, turn the screw outwards until the engine runs smoothly without any hesita- there tion. as desired The idle. idle Turn the speed stops or limits is how idle air screw lightly inwards until usually adjusted with a screw which far the throttle valve adjustment mixture can enter the noz- When the screw is turned inwards, the down as normal. As turned outwards, the valve can go lower. The position of the valve regulates the To make it is is the carburetor, seated. (Caution: If you overtighten the screw, the ta- engine to Idle prevented from going as far the screw increased. and make sure the 16-13. screw on a constant-velocity carburetor. the de- turned outwards, the amount of mixture it is Figure metered around the is ADJUSTMENT IDLE in position. it Constant-velocity carburetors have a tapered screw that which amount of in turn regulates the adjust the idle speed, first sure that the starter cable air entering engine speed. get the engine is not pushed. warm and Make any necessary idle mixture adjustments. Loosen the lock nut, is by turning the screw inwards or outwards (Figif it was loos- ure 16-15), and then retighten the lock nut ened. if one, on the idle speed screw. Adjust the idle speed FUEL SYSTEM SERVICING 239 the slide in the carburetor, screw the top back on, and re- place the rubber boot. Multiple-carburetor synchronization THIS Twin- and multiple-cylinder engines usually have one car- buretor for each cylinder. These carburetors must be syn- chronized for smooth engine operation. ders get different OR THIS amounts of If different cylin- the engine will run fuel, unevenly. Figure 16-14. The throttle valve screw adjusts idle speed. (slide) As mentioned stop idle earlier, throttle valve action is an impor- of carburetor synchronization. Idle mixture and tant part speed screws can be synchronized by turning each screw inwards or outwards the same amount of turns on THROTTLE STOP SCREW (IDLE SPEED) each carburetor. Another technique on twins is to discon- nect one spark plug wire and adjust the mixture and speed on the other cylinder, and then reverse the procedure. may when both plug wires be, however, that nected, the idle speed is It are con- too high. If so, back the idle speed screws off both carburetors the same amount until you get the desired The shop idle speed. manual service for multiple-cylinder engines usually provides a detailed synchronizing procedure using a vacuum gauge dial A set (Figure 16-18). vacuum gauge is a gauge with a vacuum hose connection. In trouble- shooting, the vacuum hose is attached to the engine's inThe amount of vacuum available is then take manifold. registered Hkw AIR SCREW Figure 16-15. Adjust the turning the screw in on the face of the cury (abbreviated as gauge cylinder's piston mixture by is uum), we can use a or out. is delivering the When moving set same using the to pump Main mixture adjustment air-fuel mixture for the the size of the main jet the throttle valve. If the main system is determined by and the position of the needle on main system is operating too rich or too lean, the needle can be repositioned on the valve. To change the setting, remove the rubber boot inches of mer- from the how fast that air (to create a of gauges to see if vac- each carburetor air-fuel mixture. vacuum gauge set. procedure in the shop service manual. The in developed by the engine cylinder depends on (IDLE MIXTURE) idle dial Hg). Since the amount of vacuum in. always follow the Run the engine until reached: carburetors must be ad- operating temperature is justed with the engine warm and choke fully open. At- tach a bungee cord (stretch cord) to the vacuum gauge mounting plate (Figure 16-19) the at the holes provided in the upper comers of the plate. Stretch the cord around the mirrors, suspending the vacuum gauge set across the bike shown in Figure 16-19. Remove the vacuum attachment plug screws han- dlebars as (usually top of the carburetor and unscrew the cap. Pull the valve found on the carburetor or manifold) from the engine, and and spring out of the carburetor (Figure 16-16). The nee- install the dle is attached to the slide with a clip. To lean out the mid-range mixture, one groove higher (called "dropping rich the mixture, place the clip in these holes (long at- tachments to the inside, short attachments to the outside). The needle usually has five grooves. The needle clip standardly comes in the fourth groove from the top (fourth stage). vacuum hose attachments move the needle"). the clip To en- one groove lower (called vacuum gauge damping (adjusting) valves closed, start the engine. Open the damping valves until stable vacuum readings are obtained. With proper damping With the adjustment, the needles will flutter slightly, but should not oscillate more than one graduation on the gauge faces. "raising the needle"). Figure 16-17 shows the positions Synchronize the carburetors according to instructions of the clip on the needle. After installing the clip, replace applicable shop manual or service bulletin. in the 240 UNIT 16: Fuel System Troubleshooting and Servicing THROTTLE VALVE THROTTLE STOP SCREW Figure 16-16. Carburetor assembly^ (Honda Motor Co.. LEAN CLIP RICH NEEDLE Figure 16-17. The main system mixture can be changed by positioning the needle. (Yamaha Motor Corp. U.S.A.) Ltd.) FUEL SYSTEM SERVICING MOUNTING PLATE RUBBER WASHER DAMPING VALVE HOSE ADAPTER HOSE ATTACHMENT Figure 16-18. A vacuum gauge set used to synchronize carburetors. (Honda Motor Co Ltd.) Vacuum gauge set attached carburetor synchronizing. (Honda Motor Figure 16-19. for Co., Ltd.) 241 NAME - Job Sheet SECTION DATE 8. Observe the 9. Locate the idle speed adjusting screw. 10. Turn the idle NOTES Instructor check idle speed and determine whether it should be higher or lower. speed screw inwards or outwards to increase or decrease idle speed, respectively. Instructor check Date completed 243 UNIT 244 16: Fuel System Troubleshooting and Servicing NEEDLE JET JET NEEDLE SLOW JET C NEEDLE JET HOLDER MAIN JET THROTTLE VALVE FLOAT Figure 16-20. Exploded views of the carburetor are found manual^ (Honda Motor Co., Ltd.) Carburetor overhaul but if you in the shop service find excessive amounts, you should check out the entire fuel system, starting at the tank. If the carburetor cannot be properly adjusted, and you sus- pect worn, damaged, or plugged carburetor might consider overhauling the carburetor. Carefully check the condition of the float, float valve you needle, and float valve seat. Inspect the float for cracks, Carburetor deformation, or signs of leakage. Especially check the float parts, overhaul involves disassembly, cleaning, inspection, and valve very carefully in the area that contacts the seat (Fig- reassembly of the carburetor. The shop service manual will ure 16-21). If the needle provide exploded views (Figure 16-20), as well as disas- worn, and both should be replaced with the corresponding sembly and reassembly procedures. size All the disassembled parts except those fiber or made rubber should be cleaned thoroughly out of and type. wom to leak past pressed air should also be used to clean the main a dle jet, pilot jet, float valve seat, and float valve. blow compressed air into the floats, altering the fuel level tion worn needle and/or seat will usually cause from the float bowl and flood the engine. new valve will allow one. its sides. Make air, A wom valve must be replaced with sure that the slide moves freely in the Never chamber will collapse and seriously affecting en- (SAFETY CAUTION: Wear when using compressed WEAR eye protec- air.) After having cleaned the parts, you should inspect them you can find the source of whatever problem caused you to overhaul the carburetor. The bottom of the float bowl should be checked for sediment. If carefully to see if or some other sediment in the gasoline, the there is filter screens in the fuel shut-off valve might be torn or dirt missing. After much mileage, some sediment is expected. A and consequently the mixture, an assembled carburetor because increasing the pressure in the float gine performance. nee- worn, the seat will also be Inspect the throttle valve for any signs of scoring. in solvent. The best way to clean out all the passages in the carburetor body is by blowing compressed air through them. Comjet, A fuel to overflow is Figure 16-21. This float needle valve shows signs of wear. (U.S. Suzuki Motor Corp.) FUEL SYSTEM SERVICING body with no binding. Check the jet needle for been contacting the noz- carburetor signs of contact. If the needle has zle Check tion, the main jet and is fuel to enter too rich. pilot jet for clogging, and stripped threads. The sult in lean much needle will allow too jet the engine, resulting in a mixture that air necessary, because a screw that difficult to adjust the pilot is deformed its air screw if will make it system. Check the pilot air pas- might be damaged. too, Inspect the starter system plunger to see the seal ta- screw for a ridge caused by having been tightened too much. Replace the it, re- might allow too much last causing a rich mixture. Also, check the fuel through, sage, as deforma- two would probably first mixtures, while the pered end on the idle if A (needle jet), both parts will require replacement. worn nozzle or on the bottom of the plunger if it is scored or cracked. Either is of these conditions will probably result in decreased per- formance. Replace the plunger if in doubt. During reassembly, you will have level adjustment. The fuel rises in the float to check the determines float level bowl before the how float closes the valve against the needle seat (Figure 16-22). float level float high the needle Too high a causes too rich a mixture, while too low a float level causes too lean a mixture. A level specific procedure along with a retor is provided for adjusting the on each model of carburetor. The is new needle valve and needle usually turned upside made between the top down, and end of the float float float is installed, a seat. The carbu- measurement is and the surface of shown in Figure 16-23. The measurement can be made with a rule or special float level gauge. The float level is adjusted by bending the small metal adjustment tang on the float (Figure 16-24) that pushes on the float bowl, as the needle valve. Bending the tang one way earlier fuel shutoff, resulting in a it the other fuel level. way lower fuel will cause level. an Bending will cause a later shutoff, yielding a higher n ^ 245 - SECTION NAME DATE IM Job Sheet OVERHAUL CARBURETOR Before you begin: Read pp. Make of Motorcycle Time Started Rat-rate Year Model Time Finished Total Time Time Special Tools, Equipment, Parts, and Materials Cleaning solvent Compressed air Roat level gauge or Eye protection rule Carburetor gasket set References Manufacturer's Shop Manual Specifications Look up the specification for float level and write it in the space below: Float level Instructor check Procedure 1. Shut off the tank fuel valve and remove the carburetor from the engine. 2. Remove the carburetor top and pull out the return spring, throttle valve (slide), and jet needle assembly. Remove the jet needle retainer and the jet needle 3. jet 4. 246 needle the needle clip Remove the float is from the throttle valve. Be sure to observe in installed. bowl screws and the float bowl from the carburetor upper body. which groove of the and assembly. 5. Pull out the float pin 6. Remove 7. Unscrew 8. Remove the pilot jet, mixture adjusting screw, and idle speed screw 9. Remove the starter valve 10. Wash the needle valve, main the all jet float and then unscrew the needle valve and needle jet from the carburetor upper body. from the upper body. assembly from the carburetor. Use compressed when using compressed air.) the parts in solvent. protection seat. 11. Put the parts on a clean rag to dry. 12. Inspect the parts for air to blow through all the passages. (SAFETY CAUTION: Wear eye wear or damage. Instructor check 13. Install the starter 14. Install all the jets 15. Install the float 16. valve assembly. and tighten them securely. needle valve seat assembly and the and measure the Invert the carburetor float. float level setting. Record your measurement below: Float level 17. Compare your measurement with float specifications. If the float level setting requires adjustment, make slight bends in the tang and recheck. Instructor check 18. Install the float 19. Install the jet 20. Replace the bowl, using a new gasket. needle in the throttle valve, throttle valve and jet making sure that the needle clip is in the proper groove. needle assembly in the carburetor upper body. Make sure that the valve cutaway faces the air intake side of the carburetor. 21. Install the throttle return spring 22. Install the pilot air or and the carburetor top. mixture adjusting screw and the idle speed screw. Instructor check 23. Install the carburetor on the engine and adjust the idle mixture and idle speed. NOTES Instructor check Date completed 247 UNIT 248 16: Fuel System Troubleshooting and Servicing KEY TERMS Carburetor synchronization: adjusting the idle speed and valve movement so that the carburetors work idle in multiple carburetors together. Float level setting: measuring and ajusting the that the fuel level in the float bowl is at Rich mixture: an air-fuel mixture much fuel or not enough in floats so the correct level. Lean mixture: an air-fuel mixture in which there not enough fuel or too much air. too mixture, which there is either is either Describe Describe 6. List four possible causes of a lean fuel mixture. 7. Explain how to service a paper air 8. Explain how to service a 9. How the twist-grip accelerator cable adjusted? is foam filter. air filter. 10. Explain how to adjust a pilot air screw. 11. Explain how to adjust idle speed. 12. How can you change the mixture of the main system? how 13. Describe 14. List four carburetor parts that should be to synchronize multiple carburetors. checked for wear during an overhaul. how a spark plug looks in an engine that is running too lean. 2. List four possible causes of a rich fuel mixture. air. CHECKUP 1 5. how a spark plug looks in an engine that running too rich. is 15. List three symptoms of a rich fuel mixture. 4. List three symptoms of a lean fuel mixture. how to measure the float level setting. DISCUSSION TOPICS AND ACTIVITIES 1. 3. Explain Disassemble and reassemble a constant- velocity carburetor. 2. Overhaul and synchronize a multiple-ciirburetor set. I he purpose of the ignition system is to provide a high- voltage spark in each of the engine's cyhnders to explode The high voltage must be the air-fuel mixture. to each of the cylinders at just the right distributed time for a power Motorcycle ignitions are classified as battery stroke. coil systems, magneto systems, or capacitor discharge systems (electronic ignition) according to the voltage is developed. In this unit, way in which the high we describe the parts and operation of each of these systems. JOB COMPETENCY OBJECTIVES When you be able 1 finish reading and studying this unit, SYSTEM OPERATION IGNITION you should to: Describe the parts and operation of a battery coil ignition system. 2. Identify the parts and explain the operation of a mag- neto ignition system. 3. Describe the parts and operation of a capacitor dis- charge ignition system. 4. Explain ignition timing is advanced with a cen- Describe the construction, operation, and technical features of motorcycle spark plugs. BATTERY COIL IGNITION SYSTEMS In a battery coil ignition system, a relatively (6 to 12 volts) is gap charge. The shown in in the low voltage is capable of jump- cylinder and igniting the air-fuel parts of the battery coil ignition system are 17-1: Figure battery, up the low voltage of the battery to enough to jump a gap at the spark plug. The coil is made up of two separate windings, the primary winding and the secondary winding (Figure 17-2). The primary winding has approximately 200 turns of relatively heavy copper wire. The secondary winding, which is in the ignition coil steps ignition ignition coil, switch, engine stop switch, breaker points, and spark plug. Battery wound around a laminated iron core that concentrates the magnetic a into field. The winding-and-core assembly power for the battery coil igni- tion system. The battery provides either 6 or 12 volts of We electrical energy. shall describe the operation of the mounted a coil cap of molded insulating material A contains the primary and secondary terminals. insulator prevents the winding assembly When grounded case. the coil is to prevent air or moisture placed at the is which porcelain from touching the made, it is from getting filled with in. top of the coil. Two pri- end of the primary are connected to each winding and carry low-voltage (sometimes called lowtension) current. The large center terminal carries high- voltage (high-tension) current When battery in Unit 20. is one-piece steel case upon the top of which There are three terminals the source of 21,000 fine mary terminals is as copper wire. The two windings are turns of very epoxy The battery many center of the primary winding, has as transformed into a momentary charge of high voltage (up to 25,000 volts) that ing the spark The a voltage high timing mechanism. trifugal 5. how Ignition coil the rider turns on the ignition key (and the breaker power source points are closed), current flows from the Ignition The ignition switch open and close the the ignition system. starting the button When through the key switch into the coil primary terminal and and stop switches is through the coil primary winding. Current goes out of the a key-operated switch that to between the power source and prevents anyone without a key from coil through the ignition wire into a switch assembly called The current flow in the circuit It primary winding creates a magnetic field inside the coil by the laminated core. In a fraction of switch usually mounted on the it used the breaker points (Figure 17-3). motorcycle. The engine stop switch depressed, is right is a push- handlebar. interrupts electrical flow in the ignition system and immediately stops the engine. This switch is that is concentrated a second (called saturation or buildup time), the current flow and the magnetic field both reach their When the breaker points open, used for quick shutdown of the engine without the rider through the primary winding having to take his or her hands off the bar. field, which depends upon this is the maximum. flow stopped. of current The magnetic flow of current, then rap- 249 250 UNIT 17: Ignition System Operation IGNITION SWITCH SPARKPLUG ENGINE STOP SWITCH CONTACT BREAKER POINTS Figure 17-1. Parts of a battery system. (Honda Motor Co.. Ltd.) CAP SPRING PRIMARY TERMINAL coil ignition SECONDARY TERMINAL PRIMARY TERMINAL EPOXYSEAL SECONDARY PRIMARY WINDING WINDING -IRON PLATES IRON CORE PORCELAIN INSULATOR STEEL CASE Figure 17-2. Sectional view of an (U.S. Suzuki Motor Corp.) coil. ignition E o ™^ CD (D o o o o O roo ^ (U Dc (/> g£ 3 o — a (0 Q. •is Q. « . CO CO ^ a> _ 3 u. - CO . CO ra -3 ^ CD 0) a. . o o o 3 cn iZ 257 258 UNIT 17: Ignition System Operation TERMINAL RETURN SPRING PLATE CERAMIC INSULATOR SEALS ADVANCE WEIGHT h FLAT CONTACT POINT CAM Figure 17-12. Centrifugal (Honda Motor Co., Ltd.) PLATE BREAKER POINTS advance 4- METAL SHELL unit. GASKET BREAKER ARM / THREADS CENTER ELECTRODE AIR GAP SIDE(GROUND) ELECTRODE Figure 17-14. Sectional view of a spark (NGK Spark Plugs (U.S.A.) Inc.) plug. The cable-to-spark-plug connection is shown in Figure 17-11. Center electrodes must be insulated, since they carry high-voltage current into the cylinder. Here, a ceramic insulator is used. The insulator has ribs formed on its outside diameter, which increases the distance between the terminal and the nearest ground. By increasing the distance to the cylinder head, the ribs also help to eliminate leakage of current (flashover). Leakage is especially a problem when the outside of the ceramic is dirty or wet. The center electrode and the ceramic insulator assembly are attached to a metal shell. the center electrode machined on The shell is insulated from by the ceramic material. Threads are the metal base of the shell to allow the spark plug to be threaded into the combustion chamber. outside of the shell are flats, used for installation and removal of the plug. Figure 17-13. Cross section of an engine showing the advance unit attached to the camshaft. (Honda Motor Co., Ltd.) tance from the center electrode trode which is On which permit a wrench is A the to be short dis- a side, or ground, elec- also attached to the shell. The distance from the center electrode to the side electrode creates the air gap that can be inserted into the engine's combustion chamber. The wire that conducts high voltage into the called the center electrode. Attached to that accepts a its top cyhnder is or spark plug gap that the current jumps to create a spark. is Since spark plugs are subjected to very high pressure, a terminal precautions must be taken to prohibit leakage of combus- connector from a high- voltage ignition cable. tion pressures. Seals are used between the metal shell and SPARK PLUGS 259 n CHAMPION REACH » -H REACH lOn ^ k Figure 17-15. Spark plugs are manufactured mensions. (Champion Spark Plug Co.) the ceramic insulator A metal gasket used is 14mm different thread In INCORRECT and between the center electrode and the ceramic insulator. 12mnn and reach di- CORRECT INCORRECT to prevent leakage of combustion pressures around the shell threads. In order to perform its basic job of providing a high- voltage spark at the proper location combustion the in chamber, a spark plug must exactly match the dimensional requirements of the particular cylinder head in which it is installed. Spark plugs are made with different shell thread diame- measured in mil- the metric system, the threads are ters. In limeters. The threaded section of the shell different lengths or reaches. is also There are several made in ACCUMULATION ACCUMULATION OF DEPOSITS OF DEPOSITS common Ground electrode reach dimensions. Spark plugs with different thread diame- and reach dimensions are shown ters in Figure and 17-15. The the combustion chamber. of the Co.) If (left) and Figure 17-16 On shown a spark plug with too long a thread reach may the other hand, reach is installed, in Figure (right), respectively. the excessively projected firing ton and valves, or end may be hit is It pis- overheat and cause engine damage. when a plug with too short a thread engine output may be reach afterwards. valve. may Spark plug operation and design firing end installed, by the be decreased and the cylinder head threads may become clogged by accumulated deposition. overheated a combustion chamber; spark plugs fits with too long and too short a reach are 17-16 is by the piston and Figure 17-16. The spark plug reach must fit (NGK Spark Plug chamber determines the reach spark plug. Figure 17-16 (center) shows a spark thickness of the combustion plug that correctly hit difficult to reinstall a correct thread To ignite the surrounding combustible mixture of air fuel in and the combustion chamber, secondary high-voltage current flows from the ignition system through the high- voltage ignition cables. This current enters the spark plug at the terminal end of the center electrode and flows the center electrode to the air gap located in the down engine's combustion chamber, where the high voltage has ionized UNIT 260 System Operation 17: Ignition (or prepared) the air-fuel mixture for burning. The current then overcomes the resistance of the gases and jumps the air gap to the side (or ground) electrode, where it creates Retracted gap plugs with recessed side electrodes have been designed for combustion chambers room vide enough physical that a spark that ignites the mixture. trodes because of piston or valve interference. Depending upon various conditions, the voltages required to overcome the gap and the resistance of the airfuel mixture may be different. For instance, the wider the ter electrode air gap, the higher will be the required voltage. Also, less voltage will be needed as opposed the air The the electrodes are clean and sharp to their being dirty compression pressure come if firing is and eroded. Finally, the if high, the voltage required to over- bum where flow or creates a We call number of is to that the oil in and collect on the spark plug it creates too new much firing resistance for current path for current flow away from the ends have been designed to prevent many motorcycles and is The conventional gap is used in the same as that used in most au- The J-gap is a conventional design that has been modified so that the side electrode extends only mid- way it possible to provide extra in faster, easier starts; fewer stalls and "false starts"; reduced fouling depoists; and, usually, longer life. The gold-palladium design not only less ignition voltage than the requires conventional electrode types, more clearance between to the center electrode. The J-gap design voltage, gives better combustion, and offers the shell and the less fouling. The projected-core spark plugs require increased physi- clearance between the firing tip and the piston or cal The incoming valves. air and fuel cools the high speeds. At low speeds, the firing tip runs firing tip at at long periods of slow-speed running. A surface-gap spark plug does not have a conventional firing end. Instead, that arcs which is it has a relatively flat sparking surface between the center electrode and the metal also requires less Surface-gap plugs are designed for use with capacitor discharge systems, which have the electrical characteristics necessary to take advantage of the surface-gap design. CONVENTIONAL RETRACTED GAP J-GAP INSULATOR CENTER ELECTRODE 1 SIDE shell exposed within the combustion chamber. good fouling protection for a two-stroke engine. AIR GAP tempera- tures higher than those of conventional-type plugs. In this manner, deposits can be burned off the spark plug during such a condition n fouled spark plug. firing fouling (Figure 17-17). tomobiles. performance, resulting end of the spark plug must be designed end. This burned oil (called carbon) eventually builds up A available for special requirements. This insulator for far better self-cleaning of fuel deposits and the fuel tends to air gap. is semiprecious metal alloy makes but also provides motorcycles, especially two-strokers, to the point gold-palladium spark plug with a small-diameter cen- gap must also be high. provide a good surface for spark discharge. The problem in A do not pro- for conventional-type elec- ELECTRODE GOLD PALLADIUM PROJECTED CORE I J Figure 17-17. Firing-end designs for SURFACE GAP ^y motorcycle engines. (Champion Spark Plug Co.) KEY TERMS Heat range Spark plug codes The spark plug firing end is mounted in the engine's combustion chamber and subjected to very high temperatures, so of course it must be designed to remove this heat. The pathway of the heat is away from the firing end. Heat The spark plug must be matched moves up dimensions, as well as the ceramic insulator to the metal shell out into the engine's cylinder head, to be air and then removed by the flow or liquid cooling. Spark plugs are designed to operate within a certain tem- Heat range describes the ability of a spark plug to conduct heat away from the firing end. It is determined by the distance that heat must flow from the firing shell. If the heat path is long, the firing end will maintain a high temperature. The plug short, heat is removed more and the plug is is then re- pathway ferred to as a hot spark plug. If the heat-flow is from the spark plug, easily called a cold spark plug. Figure 17-18 shows a comparison of cold and hot spark plug heat paths. The operating temperatures of the spark plug tips are a compromise between carbon and oil fouling on the one hand and preignition and electrode burning on the other. Carbon and properly if oil be burned off of the electrodes will not the temperature of the spark plug tip cold. Misfire will probably occur been built up on the electrodes. tip due On is to deposits that too have the other hand, if the area operates at too high a temperature, the insulator end ture. itself could get hot enough to ignite the air-fuel mix- This random ignition with no spark tion. Preignition is violent for a long enough time, nents. Electrode burning it is called preigni- and uncontrollable. it If continued could damage engine compo- and corrosion will be accelerated with excessive temperatures at the tip, thus shortening the is That installed. is, their spark plugs. There turer all The code, the other technical features of a combination of hot and cold spark numbers and printed on the insulator or stamped on the shell. is no universal code. The catalog for each manufacmust be consulted to identify a particular spark plug code. Spark plug Inspection A visual inspection is made of each plug. Disconnect the spark plug cable and unscrew the plug. First, check the spark plug electrodes for wear or damage. The center elec- trode should be fairly clean and even, and the side electrode should have an even thickness. Then check the ce- ramic insulator for cracks or chips. Sears should be sound and undamaged. Discard plugs that are fouled or damaged. If the plug appears sound, measure the gap with a feeler gauge, and regap as needed by bending the side electrode. KEY TERMS Battery coil ignition system: an ignition system which uses the energy in a battery stepped up by a coil to provide a high- voltage spark. Breaker points: an assembly that is equivalent to a chanical switch opened by a cam me- driven by the engine crankshaft; used to induce a high-voltage current in an ignition coil. HOT COLD A must have the cor- plug manufacturer has developed a code to specify these useful life of the spark plug. Figure 17-18. correctly to the engine in the plug and heat range. Each spark rect thread diameter, reach, letters, is perature range. end to the metal which 261 plug. (Champion Spark Plug Co.) 262 UNIT 17: Ignition System Operation Capacitor: an electronic device consisting of alternate plates of conductive to store and insulative material that is used Capacitor discharge ignition system: an ignition system energy stored in a capacitor to develop high Coil: an electrical device which uses primary and secondary copper windings surrounding an iron core to step up low voltage Condenser: an electrical device used in an ignition system CHECKUP Identify the parts of the battery coil ignition system 2. 3. 4. 5. 6. 7. to develop the pri- voltage. Spark plug: the ignition system component which provides an air gap for the high voltage created by the ignition names in the spaces provided. the gap to create a spark in the Timing mechanism: a set combustion chamber. of weights and springs driven by the engine camshaft or crankshaft; used to to high voltage for ignition. to store electrical energy to prevent breaker point arcing. 1. ignition system: an ignition system that uses ro- magnets instead of a battery system; the current produced by the high voltage jumps voltage. writing their tating mary and quickly discharge current. that uses the Magneto by breaker points into a new engine speed increases. move the position to advance ignition as CHECKUP Identify the parts of the ignition coil in the by writing their names spaces provided. 9. 10. 11. 12. 13. 14. 15. 16. 17. Identify the parts of the names 18. 19. 20. 21. 22. 23. in the magneto spaces provided. ignition by writing their 263 264 UNIT 17: Ignition System Operation Identify the parts of a spark plug by writing their names in the spaces provided. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. DISCUSSION TOPICS AND ACTIVITIES 1. Disassemble a batter\' coil ignition system and iden- tify the parts. 2. Disassemble a magneto ignition system and identify the parts. f^ motorcycle with ignition system problems hard to start, at The all. may run poorly ignition when may may started, or be not run system components, especially the spark plugs and breaker points, eventually wear to the no longer develop the high point that the system can volt- To age required for proper ignition of the air- fuel mixture. prevent these problems from occurring, the ignition system must be serviced system is at regular intervals. Ser\'icing the ignition usually called an ignition tune-up. torcycle technician must be able A good mo- to determine the cause of an ignition problem and then perform the necessary servicing. AND SERVICING JOB COMPETENCY OBJECTIVES When you be able finish reading and studying this unit, you should to: 1. Explain how to troubleshoot the ignition system. 2. Remove, clean, regap, and install spark plugs. 3. Remove, replace, and gap breaker points. 4. Adjust ignition with timing a test so that the shell head, as shown points light, Check high-voltage ignition (spark plug) cables for re- sistance. Explain 6. how Figure 18-1. (Safety Caution: the Make sure you hold the plug by the insulated spark plug wire Crank or kick the engine. If you see a strong blue spark the center and ground spark plug electrodes, then you have ignition, and the problem lies outside the jump between is no spark, you know you have an ignition system problem. tests. If you do not get a spark plug, TROUBLESHOOTING THE IGNITION SYSTEM In order to run. in ignition system. If there to test an ignition coil. Describe the three condenser 7. makes a good grounded contact with boot to avoid getting shocked. checker, or timing light. 5. SYSTEM TROUBLESHOOTING IGNITION First, eliminate the ble. an engine needs compression, fuel, and a good the fuel spark, the trouble may involve system, or engine compression. spark plug as a possible cause of trou- Remove each one of the engine's spark plugs, and vis- ig- Troubleshooting the ignition sys- nition at the right time. tem involves making sure that the engine has these basic elements. The ignition system provides a high-voltage spark in each of the engine's cylinders bum the air-fuel mixture. enough An at just the correct on the road is have ignition problems. ous potential problem areas. has fuel. Make connected. If the first Check make When ei- eliminate any obvi- the tank to see whether a visual inspection of secondary wires to fast ignition motorcycle that loses power and quits likely to ther of these malfunctions occurs, it may have to run, but that will not start, trouble. Similarly, a time to engine that cranks over all the primary and become dis- sure a wire has not system looks complete, you should then make a spark, or spark intensity, test, check to which determine whether the ignition system is is a quick provid- ing a spark. To make the test, disconnect the spark plug wire from one of the spark plugs, and then remove the spark plug from the engine. Reconnect the spark plug wire to the spark plug. Hold the spark plug against the cylinder head Figure 1&-1. Testing the ignition system spark (Champion Spark Plug Co.) for 265 Aluminum Throw-Off Nonnal Light tan to gray color and slight electrode wear indicate correct heat range. Change plugs at regular intervals using same heat range. Core Bridging, Gap Bridging Aluminum deposits on el&ctrodes and Insulator core nose. Caused by first stages of preignition within the cylinder which melts the aluminum alloy of the piston crown. Do not install new plug until piston is examined and the source of preignition is determined. Overheating Combustion particles wedged or fused between the electrodes or the core nose and shell. Both core bridging and gap bridging are caused by excessive combustion chamber deposits striking and adhering to the spark plug's firing end. They originate from the piston and cylinder head surfaces. These deposits are formed by one or a combination of the following: Excessive carbon in cylinder. Use of non-recomImmediate high-speed operation oils. after prolonged low-speed running. Imporper ratio mended Electrodes badly eroded. Premature gap wear. Insulator has gray or white "blistered" appearance. Incorrect spark plug heat range (too hot). Ignition Consistent high-speed timing overadvanced. operation. of fuel/oil mixture. Preignition Wet Fouling Damp firing black carbon coating over entire Forms sludge in some extreme cases. or wet, end. Wrong spark plug heat range (too cold). Prolonged slow operation. Low-speed carburetor adjustment too rich. Improper ratio of fuel-to-oil mixture. or defective breaker points, resulting in lack of voltage. is Worn IVIelted electrodes and/or white insulator indicates sustained preignition. (Insulator may be dirty due to misfiring or debris in the combustion chamber). Check Figure 18-2. Spark plugs can be compared Spark Plug CoJ 266 for correct plug heat range, proper lubrica- and/or overadvanced ignition timing. Determine the cause of preignition before putting engine back into service. tion to an analysis chart. (Champion TROUBLESHOOTING THE IGNITION SERVICE ually inspect the electrode area. If there it is 267 excessively wet, an excessive supply of fuel, indicating an air-fuel is mixture that is too rich. Excessive wetness can also indi- cate a defective spark plug. Dryness, indicates an air-fuel mixture that analysis chart (Figure 18-2) on the other hand, too lean. is may be used A spark plug to further diag- nose problems from the appearance of the spark plugs. A fouled or improperly gapped spark plug will not ignite the air-fuel mixture in the best, combustion chamber or produce inadequate ignition. engine, you may On one or more find a difference in color of of the spark plugs. If all will, at a multiple-cylinder except one are normal, you can suspect the associated cylinder of misfiring or mechanical Figure 18-4. Metal from one breaker point can transfer to the other. (Yamaha Motor damage. Corp. U.S.A.) you do not get a good spark and the ignition system uses breaker points, the points are the most likely source of the problem. The breaker point surfaces must be in good condition and the space between the breaker points must If be correct, or the system will not be able to develop any Figure 18-5. Ignition breaker point file. secondary voltage. Remove the cover over the breaker points the breaker point surfaces. points gradually and inspect After a period of time, the become burnt and pitted (Figure 18-3). Eventually, metal from one point transfers to the other, as shown Figure 18-4, and the pitting and surface deterio- in ration create The contact. enough resistance to prevent good electrical ignition system then fails to function prop- erly. Another possibility the seal is that oil may gradually seep past and coat the points or wiring. The oil will bum onto the points, creating an insulating film that must be re- moved The in order for electrical contact to be made. fiber cam follower mounted on the pivoting point arm rubs against the cam. Eventually, down, resulting in a reduction this cam wears of the point gap and re- Figure 18-6. Filing the breaker points. Once this happens, new gap opening. motorcycle running, you can make a tarded timing of the affected cylinder. the points must be adjusted In order to get the to a temporary repair by cleaning the breaker points. Breaker points are cleaned with an ignition breaker point ure 18-5). To clean the points, run the file file (Fig- between them (Figure 18-6) until the grey deposits and pits have been removed. Then spray the points with ignition point cleaner and snap them shut on a white business card (or paper of hard texture), repeatedly pulling the card through until no more carbon or metal particles come off on the card. Check the points to see that they are properly aligned, and that they are not twisted or offset from each other (Figure 18-7). If they are not properly aligned, bend the fixed contact support with either pliers or the recommended special breaker point bending tool. (Never bend the movable breaker arm.) The points should align and be in full, even contact with each other. Figure 18-3. Breaker points eventually become pitted and burned. (Yamaha Motor Corp. U.S.A.) After cleaning the points, you will need to reset the gap between them. First rotate the opens the points to their engine until the ignition cam widest position. Then slip a .4- UNIT 268 18: Ignition System Troubleshooting and Servicing PROPER LATERAL ALIGNMENT LATERAL MISALIGNMENT After regapping the points, check for spark again. system now works, the engine should run. If there no spark, you will have If the is still perform a complete ignition to tune-up as described in the next section. IGNITION \ CORRECT LATERAL MISALIGNMENT BY BENDING FIXED CONTACT SUPPORT NEVER BEND BREAKER LEVER SYSTEM SERVICING The parts of the ignition vals recommended by when there is a system must be serviced at inter- motorcycle manufacturer or the problem with the system. Common ignition servicing procedures include cleaning and gapping spark plugs; replacing and adjusting breaker points; setting ignition timing; and performing electrical tests on the coil, condenser, and high-voltage ignition cables. Spark plug servicing WORN NORMAL Spark plug removal and servicing every ignition tune-up. Use is an important part of a 6-point deep spark plug socket (Figure 18-9) for spark plug removal and installation. DIRTY NOT PARALLEL slip (.016") feeler gauge into the gap. If fit. screw (1 an adjustment or 2) as in must be a tight Figure 18-8. Insert a screw- driver into the adjustment slots (3 or 4), and open or close the points until the feeler gauge indicates the correct gap. Then retighten the lock screw and recheck the gap. If the ignition uses two shaft until the point. sets of breaker points, rotate the second Then perform set the of points opens to same its be placed in the socket and head by hand. Since, as mentioned earlier, the condition of each spark plug necessary, loosen the point lock is shown It may it started into the cylinder Figure 18-7. Point alignment, (Top: U.S. Navy. Bottom: U.S. Suzuki Motor Corp.) mm Spark plug sockets are designed to hold the spark plug firmly so that cam widest steps over again. it is tells a a story about the cylinder good idea method of doing a block of to this is to wood it make was removed from, An easy a spark plug holder from keep the plugs in order. (Figure 18-10). Place the plugs in the holder with the terminal end down. They can then be inspected without removing them from the holder. Arrange the plugs in the same order as the cylinders, so that a de- fective plug can easily be identified with the appropriate cylinder. After you have sulator removed and the electrodes. the plug, closely inspect the inIf they are not damaged, you LOCK SCREW ADJUSTMENT/ /(^ SLOTS \^ K "^ ADJUSTMENT SLOTS BREAKER POINTS LOCK SCREW Figure 18-8. Adjusting the breaker point gap. (Yamaha Motor Corp. U.S.A.) Figure 18-9. Use a spark plug socket for spark plug rennoval and installation. Keep in order so you can relate back to the cylinder. (Champion Spark Plug Co.) IGNITION SYSTEM SERVICING 269 Figure 18-10. As a spark plug is removed, should be placed in a holder for inspecit tion. can clean and regap the spark plugs. However, if the plugs Figure show any damage, have high mileage, or have been cleaned before, they should be replaced with new blasts a fine abrasive at the electrode area its are located. 18-11), which where the depos- Follow the instructions of the cleaner man- ufacturer carefully. Plugs should be cleaned until the inside of the shell, the entire insulator, and the electrodes are clean. down However, blast the insulation cleaning for too long will wear and damage the plug. Plugs which cannot be completely cleaned with a reasonable amount of blasting should be replaced. Clean the top insulator and terminal with a cleaning solvent to remove all oil and dirt. which may not have been visible before. If good condition, the plug appears to be in end of the the center electrodes should be filed lightly to provide a flat, square surface. To file the electrodes, bend the ground electrode from the center electrode breaker point flat less voltage is to allow room away for a thin ignition File the electrodes of the plug until the file. surfaces are (Figure 18-12). Twenty-five to 40 percent required to the center electrode than fire a plug with sharp edges on Do one with round edges. not file the center electrodes of gold-palladium or other fine center wire spark plugs. After cleaning, inspect the plug carefully for cracks or other defects electrodes. the Filing ones. Spark plugs that are coated with carbon deposits can be cleaned in a spark plug cleaner (Figure 18-12. (Champion Spark Plug Co.) After filing, or if you are installing new spark plugs, you A must adjust the spark plug electrode gap. setting is necessary for efficient causes rough running low speeds; too wide a gap engine missing because voltage in the jump at The the gap. correct gap Too narrow firing. setting is a gap results insufficient to is determined for each engine by and it should be maintained. manual for the recommended set- the motorcycle manufacturer, Check the shop service ting. A spark plug gapping tool (Figure 18-13) the opening. It and a bending tool. to bend To it 18-11. Cleaning (Champion Spark Plug Co.) a spark plug. more ac- away from the center electrode. bend the ground electrode with the bending tool as shown in make Figure 18-14. Bend the pushing wire a It gauge should fit it closer to gap smaller and make the center electrode to through the space. 18-15). a gauge. The over the ground electrode and allows you the center electrode to away from Figure fits flat closer or farther adjust the gap, gap by used to gap Round wire gauges provide curate reading for spark plugs than does a bending tool is includes a set of round wire feeler gauges the it wider. required farther Check the thickness with a light drag (Figure UNIT 270 18: Ignition System Troubleshooting and Servicing WIRE FEELER GAUGES BENDING TOOL Figure 18-13. Spark (U.S. Navy) gapping plug tool. Figure 18-16. Start the spark plugs hand. (Champion Sparl< Plug Co.) by ated by the crankshaft are usually found under a cover on the lower left side of the engine. Those operated by the camshaft are located under a cover on the top Some the engine. cam area of crankshaft-operated breaker points are The flywheel, of course, has located behind a flywheel. to be removed to service these breaker points. Single-cylinder engines use one set of breaker points. Twin- and multiplecylinder engines use Remove points, Figure 18-14. Adjusting the spark gap. (Champion Spark Plug Co.) two or more cover the sets of points. provide access to the breaker to and unscrew the point wire securing screw (Figure 18-17). Completely remove the point lock screw and plug the entire point Place the assembly up off the point base new set lift plate. of points into position by slipping the point assembly locating pin into the appropriate locating hole in the base plate. Insert and tighten the point lock screw. wire Then to the finish the point assembly. (A) CORRECT (B) plate After cleaning and gapping, the spark plugs are rein- and Use start the plugs by hand (Figure 18-16). Then use a to tighten them to the Using a torque wrench ensures ened just the correct amount. threads could be stripped; enough, it and regapping the that the spark plug If if recommended by the insulator washers. POINT LOCK SCREW NT WIRE torque. is tight- you overtighten the plug, you don't tighten the plug POINT BASE PLATE could vibrate loose. Replacing breaker points Breaker points should be removed and new ones installed at the intervals recommmended by the manufacturer. As mentioned previously, some breaker points are operated by some by the camshaft. Those oper- the engine crankshaft, new lead wire should not touch the the spark plug socket to hold each spark plug, torque wrench its point The point point base plate and should be insulated from the base INCORRECT Figure 18-15. Measuring gap. (U.S. Navy) stalled. replacement by attaching the point stationary Figure 18-17. Removing and replacing breaker points. (Yamaha Motor Corp. U.S.A.) IGNITION Be sure not to touch the breaker point surface, as the oil on your hands can cause enough of a resistance Some misfiring. be lubricated to cause point sets require that the rubbing block Check with high-temperature grease. the shop service manual for recommendations. the correct gap, as explained in the previous section. gauge you use sure that the feeler the engine Kick over and observe the point action; the points should meet squarely. If they make contact on only one you can gently bend the stationary point side, Make perfectly clean. is into align- ment. mounted to the elongated slots point cam is in the plate. In new breaker points are installed, you are ready to check and adjust the ignition timing. The ignition timing correct when the breaker points open at just the right time in relation to the position of the piston. As explained Unit 17, the ignition system delivers a spark the instant Hence, we want the breaker points open. bing block will contact the and breaker cam the piston, advancing the ignition timing. We as the can also rotate the base plate cam turns, i.e., in the same occur later in relation to the position to introduce the you must position the piston place the breaker points affects ignition tim- points are spaced too far apart, the in the cycle and ignition sooner in relation to piston position. On cam will will occur the other hand, the points are spaced too close together, the cam will if open the breaker points later and ignition will occur tion to piston position. These considerations are why gap- later in rela- ping the breaker points accurately to specifications important. They are also why of the pis- is so timing should be checked af- is done in the in three steps. First, cylinder in exactly the should be to get ignition, usually just before it that the breaker points are just starting to piston is it correct, open when the in the correct position. Third, if the timing is not you must loosen the base points in a position in open them sooner cam The spark reaches top dead center. Second, you must check to see dead center. If the direction clockwise. This will cause the breaker point assembly one The gap between The earlier in the cycle. spark will then occur earlier in relation to the position of spark into the cylinder just before the piston reaches top ter the loosen the base plate ton, retarding the ignition timing. is ing. we rotate the base plate Setting the ignition timing After the in Figure 18-18, the breaker turning clockwise. If point assembly counterclockwise, the breaker point rub- will then adjustment is in engine by screws which pass through to contact the rubbing block later in the cycle. Ignition timing 271 breaker points mounted to a base plate. The base plate turn hold-down screws and After installation, the breaker points must be adjusted to SYSTEM SERVICING way plate and move the or the other to get the which they are just barely open. Timing procedures and specifications are different different types of motorcycles. Many for two-strokers use a procedure which calls for a dial indicator to determine the position of the piston. a spark plug To use this procedure, you remove from the cylinder head and then mount a dial indicator to the top of the head, allowing the dial indicator tracer pin to stick through the spark plug hole and contact the head of the piston (Figure 18-19). breaker points are serviced. Timing is moving the base plate on which components of the CD igmounted. Figure 18-18 shows a set of adjusted by the breaker points (or solid-state nition system) are DIAL INDICATOR HOLD DOWN SCREW SLOT BREAKER POINTS TRACER RUBBING BLOCK Figure 18-18. Timing the base plate in maha Motor Corp. is adjusted by moving relation to ttie U.S.A.) cam, (Ya- Figure 18-19. A dial indicator mounted with the tracer pin through the spark plug hole. (Central Tool Co.) PIN UNIT 272 18: Ignition System Troubleshooting and Servicing FULL ADVANCE MARK Figure 18-21. A test light used to check breaker point opening. (Honda Motor Co., Ltd.) Test Light A T" MARK TOP DEAD CENTER Figure 18-20. Ignition timing marks on the (Honda Motor Co., Ltd.) when there A the highest reading on the top dead center, on dial indicator. Set the zero up exactly with the the dial indicator face to line dial indi- cator needle. Rotate the flywheel back and forth to be sure does not go past zero. Then rotate that the indicator needle backwards a recommended number of the engine slowly thousandths of an inch or hundredths of a millimeter on the proper position just dial indicator, putting the piston in the to marks remove get the piston in the correct position. These timing on the flywheel, so you will have to the left-side engine cover. Different manufacturers use different marks, but those There on the flywheel. The the flywheel T is Figure 18-20 are typical. Two used to dead center. line stands for the top T up line lines top dead center. is at is lines are inscribed rotated so that the with the notch, the piston it in marks on the flywheel. align the When shown a notch on the engine crankcase that is Of course, could be on either compression or exhaust stroke. The way thumb in best you can The F the F to tell is to remove a spark plug and put your the spark plug hole. feel the On high compression line. When up with the notch, and the piston on is a compression stroke (not exhaust stroke), the piston that shown is in the correct position for ignition, usually just before top light is to determine does not light. As lead is connected circuit to the connecting wire or the metal the points are closed, the current the points open, the current can no use the test light, test light, and the bulb it lights lights. Finally, tighten the by rotating the engine set the piston in the correct first lamp hooked up. Then breaker point base plate one to way rotate the or another until the bulb base plate. Check your results make sure that the bulb lights as the piston reaches the correct position. Checker Points A points checker connect it is a meter with two leads into a circuit (Figure 18-22). that are One lead used to is con- nected to the grounded stationary breaker point (or any good ground), while the other lead is connected movable breaker point (or the circuit feeding it). When the points are closed, the circuit swinging to the right (Figure open, the circuit swings is to the left, is to the continuous. A whether the points are just not very accurate. Instead, checked with either a test light or a continuity tester, usually called a points checker. 18-22, top). As the points broken and the points checker needle showing no continuity (Figure 18-22, bottom). in the correct position and the points checker connected, rotate the base plate back and forth until better check breaker point One connected to the at the When position with the test breaker point base is to up. barely opening. This could be done merely by observing breaker point opening is goes to ground through the the breaker points, but that is connected Figure 18-21. longer go to ground across the breaker points. Instead, With the piston step is in goes across the closed breaker points to ground, and the dead center. The next can be test light needle on the points checker shows this continuity by in the cylinder. advance is breaker arm itselO- the compression stroke, line is the firing or ignition line is lined light test ground and the other To four-stroke engines have timing marks to help you are usually The a voltage in the circuit. breaker point (either before the top dead center location. Most is used to determine when the breaker points open. opening is at When clips. properly connected into a circuit, the bulb will light up flywheel, Rotate the engine until the piston socket with a 12-volt lightbulb test light is a lightbulb connected to two leads which have alligator the points checker needle setting is shows no continuity. The then tightened down. Recheck the by rotating the engine and observing the points checker. IGNITION SYSTEM SERVICING 273 POINTS CLOSED POINTS CLOSED: CONTINUITY Figure 18-23. A timing light used to check timing. (Sun Electric Corp.) dynamic When the engine is running, the ignition impulse causes the timing light to flash each time the number-one spark plug receives high-voltage current. This flashing light V, rected at the timing marks on effect of the light makes freeze. It is the flywheel, marks appear the flywheel easy to see whether the marks are aligned, they are not, the base plate must be timing. In is di- and the strobe some models, moved to if to correct the marks are observed through the an inspection plug which must be removed. POINTS OPEN POINTS OPEN: NO CONTINUITY Figure 18-22. A points checker used to Checking spark plug cables High-voltage ignition cables break check point opening. time. Timing Ligtit More and more motorcycles are now being timed while running with a timing light (Figure 18-23). This procedure is often called The the dynamic riming. typical timing light has a set of leads connected to motorcycle battery for power. Some are connected into 5- volt AC outlet. power from a An induction pickup (shown in Figure 18-23) goes around a larger tester or receive the high-voltage lights use ignition 1 1 cable. Other types of timing an adapter that allows the high-voltage ignition cable to be connected to the timing light and the spark plug at the same time. in large In either type, electrical energy capacitors inside the timing light. A is stored high-voltage impulse from the ignition system causes this energy to be discharged into the flash tube of the timing a bright flash of light. ing a lead the The impulse from the timing number-one cylinder. treme moisture and oil deteriorate If the spongy or is light to the light, creating received by connect- spark plug cable for rapidly. brittle, You can check suring down after a period of Repeated heating and cooling, combined with ex- it exposure, cause the insulation to boot or cable excessively a spark plug cable electrically by mea- resistance with an its is should be replaced. ohmmeter (Figure 18-24). (Unit 19 explains the use of an ohmmeter.) Calibrate the ohmmeter and turn the range selector knob Then disconnect one spark plug cable to the zero line, to the highest scale. from a spark plug, and disconnect the other end from the Connect one ohmmeter test lead to the spark plug ca- coil. ble terminal and the other lead or terminal on the coil end. to the matching metal Then record insert the resistance, and repeat this procedure for each of the spark plug cables. Check the readings obtained with the specifications. are usually given in ohms per foot. plug cable, the higher the resistance spark plug cable whether it ohmmeter against Spark plug cable resistance specifications may have to The longer the spark is. The length of the be measured to determine meets specifications. Replace the spark plug ca- UNIT 274 18: Ignition System Troubleshooting and Servicing SECONDARY TERMINAL SPARK PLUG CABLE PRIMARY TERMINAL GROUNDED FRAME OHMMETER Figure 18-25. Checking secondary wind(Honda Motor Co., Ltd.) ings. Figure 18-24. Checking spark plug cables for resistance. bles if the measured resistance is higher than the specifi- cations. Checking the The ignition coil best check of the ignition coil is a check for a spark across the spark plug electrode. If you get a the coil coil. A coil. If is is A good. weak spark can be due good spark, to a defective good way to check is to substitute another, good you now get a good spark, you know the old core defective and must be replaced. Most manufacturers have a coil tester, and secondary windings. circuit the checked for resistance with an may also be ohmmeter. Remove the priignition coil mary and secondary wires from the ignition coil. Follow the manufacturer's instructions and calibrate the ohmmeter and turn the range selector knob to the highest scale. Then connect one ohmmeter test lead to the secondary terminal and the other to the grounded frame (Figure 18-25). Check the resistance reading against specifications. If the reading is higher than specifications, replace the ignition To check point capacitor (condenser) instantly stores a static electric in coil. the coil's primary circuit, disconnect the pri- mary and secondary wires or leads from Then calibrate the ohmmeter. Connect one the ignition coil. tester lead to charge as the breaker points separate, and the energy stored in the capacitor the points are closed. If electrical them to is excessive, replace the ignition coil. the current in the primary winding of the ignition coil. If the breaker points show excessive wear, or the spark (and the ignition coil pacitor. Before capacitor to is in good is weak condition), check the ca- checking or testing, however, ground the itself, as shown in Figure 18-27, to discharge the stored electrical charge. The capacitor is tested condenser provides tance when for the capacitor, an burning of the breaker points, greatly affecting the flow of grounded frame (Figure 18-26). Compare the resistance to specifications. If the resis- discharges instantly were not bum. The capacitor minimizes 28) for series resistance, ohmmeter it charge would arc across the separating breaker points, causing the ignition coil primary terminal, and the other lead to the reading from the primary. Checking the breaker point capacitor (condenser) The breaker Circuit The secondary coil most have a test procedure for the resistance of the coil's primary and Secondary Figure 18-26. Checking the (Honda Motor Co.. Ltd.) in the on a condenser tester (Figure 18i.e., the amount of resistance the primary circuit. Series resistance and tested for leakage; high affects ignition coil output is leakage indicates that the condenser insulation cannot with- IGNITION Stand the demands of the ignition system. also checked for capacitance, and pitting. Too low SYSTEM SERVICING which 275 The capacitor is affects point arcing or too high a capacitance will cause rapid point pitting. The manufacturer's instruction manual should be followed when performing capacitor tests. If a condenser fails any one of the tests, it must be replaced. A new condenser should be tested prior to installation to Figure 18-27. Discharge capacitor (condenser) before testing. (Honda Motor Co., good condition. Ltd.) TO IGNITION POWER SOURCE COIL CONDENSER V> TO IGNITION COIL (DISCONNECT THE SOLDERED JOINT IF ) USED.) TESTER SET THE ELECTRO-TESTER ON THE "M J fi" POSITION Figure 18-28. The capacitor is checl=^^ I H2SO4 I H,0 DISCHARGED Figure 20-7. Chemical action (Ford Motor Co.) rials. Discharging and recliarging the cell in a battery dunng charging and discharging. over and over again will eventually wear out the components, since the chemical reversals are never cell will 100% effective. Finally, the reach a stage where the plates cannot be made dis- with a few small plates will discharge very quickly On supplying a high current. many large plates can supply current for a longer period of time. The most common method used similar through the application of an electric current. when the other hand, a battery with of a battery is the to specify the capacity ampere-hour rating (AHR). AHRs are calculated by multiplying the battery discharge current, in amperes, by the number of hours the battery Battery rating is capable of supplying that current. Battery performance is rated according to a variety of labo- by the ratory test procedures that have been established battery manufacturers. Every manufacturer uses the same procedures so that one manufacturer's battery pared with another's. When a battery is may replaced, be comit is im- In order for a battery's advertised hour rating was measured must be known. period of many hours, hours of current than formance such as occurs rating. all three- or six-cell storage batteries have the same voltage, they may differ widely in capacity. Capacity is a measure of how long a battery can supply current. The capacity of a battery is determined by the amount of active material and electrolyte in each cell. The number of plates and the size of the plates a battery has will determine how long chemical activity can continue in a cell. A battery to If a battery is slowly discharged, producing low-amperage current over a portant that the replacement battery have a comparable per- While ampere-hour rating be useful, the particular time period for which the ampere- it will if it is produce discharged far at a more amperevery rapid rate, when it is operating a starter motor. Most motorcycle batteries are rated on a 10-hour will dis- Based on this rate, a 12 ampere-hour battery deliver 1.2 amperes of electrical current for 10 hours. charge (1.2 rate. Ax 10 hours =12 ampere-hours.) It is not true, of course, that the battery will deliver 12 amperes for more likely, it length of time. would deliver only about 6 amperes 1 hour; for that CHARGING SYSTEM OPERATION CODE INTERPRETATION 12N12A-4A-1 — — — A — — A — — N Nominal voltage (12 volts) Initial for Nippon (Japan) 12 Ampere-hour capacity 12 4 1 at 6 "N" indicates battery voltage. Number immediately following "N" indicates preceding letter N 6 ampere-hour capacity. Other symbols identify the physical construc- 3 tion of the battery. B AH) J IS battery identification symbol Terminal position code Vent tube position code Yuasa battery identification number — — — — — Nominal voltage (6 volts) Initial for Nippon (Japan) Ampere-hour capacity at 10 hour discharge rate (6 AH) Terminal position code Vent tube position code Figure 20-8. Typical battery identification code. (Honda Motor Co., The printed rating of a battery on the side of the Ltd.) often specified on a code battery, as are other technical Since each manufacturer has features of the battery. own is 10 hour discharge rate (12 6N6-3BCODE INTERPRETATION: Yuasa 12N12A-4A-1 Battery Number 301 its IGNITION SWITCH code, you must have the technical literature for any particular battery in order to understand turer's code and interpretation are shown it. in One manufacFigure 20-8. CHARGING SYSTEM OPERATION The function of the charging system is to generate electrical energy to power the motorcycle's electrical system and to charge the battery. The main components of the charg- ing system are the battery, alternator, rectifier, and voltage The regulator (Figure 20-9). the rest of the charging works together with battery system to supply electrical energy. The charging system as a whole senses the battery's state of charge and works to keep the battery charged. The alternator converts some of the mechanical energy of the engine into electrical energy. energy to supply the demand of system when the engine the is It generates electrical the motorcycle's electrical running. In addition, it restores chemical energy of the battery by sending current REGULATOR/ Figure 20-9. Charging system. (Honda Motor Co.. Ltd.) The voltage regulator senses alternator and were allowed limits to it the output voltage of the to a safe amount. become excessively If this voltage high, the battery and tlirough the battery in a direction opposite to the current other electrical equipment could be damaged. that flows The way the battery and alternator work together is shown in Figure 20-10. When the engine is not running, or when its rotational speed is low. the battery is the only source of energy for the electrical system (Figure 20- The through it during discharge. changes the alternating current developed by the alternator to direct current, which is used to charge rectifier the battery and power the electrical equipment. UNIT 302 20: Battery and Charging System Operation and Servicing Direction of lines of force f^ Low Direction of electron current flow. through lamination. Engine Speed AlElectrical System (Load) Battery provides (b) Medium all electrical energy to system Engine Speed Magnet at point of Lamination maximum Assembly field intensity. I A- Ballffv . (-) Alt I System requiremenis shared by battery and alternator. ©f Medium to High Engine Speed ^ Batt ery Alternator Regula & Figure 20-11. A basic alternator. (Kawasaki Motors Corp. U.S.A.) Electrical ,T i-l System (Load) Rectifier t ^ > i *-^ Alternator provides electrical energy to system and Basic principles of the alternator also restores battery. A basic alternator can be constructed from a single coil of Figure 20-10. The alternator, regulator, and battery work together to power the electrical system. (Kawasaki Motor Corp. USA) of thin iron strips past which a single magnet As both alter- magnet turns, the flow of lines of force between the north and south magnetic poles and reached where the output through the lamination assembly creates a strong magnetic wire wound around As (Figure 20-11). 10(a)). rotational speed of the engine nator output increase, a speed is and the voltage level of the alternator matches that of the battery. field At magnet this point, the battery and the alternator share in provid- ing the current (electrical energy) requirements of the electrical The alternator is sometimes dynamo, or a magneto. develop electrical energy. called an AC/generator, a system (Figure 20-10(b)). During medium to high speed, around the in the coil magnetic the alternator supplies is The to the buildup and collapses around the this reverse flow of current that enables the battery to be charged during engine operation. alternator is AC, changes, the direction of cur- by the alternator is is the reason called alter- current. Alternator construction an alternating-current generator that uses the principles of conductors coil that the current generated nating, or THE ALTERNATOR The and current with each 180-degree swing of the magnet. rent flow through the coil also changes. This is rotated Since the polarity of the magnetic field that builds up current through the battery in reverse direction (Figure 20It number and collapse of the energy for the electrical system and also pushes a flow of 10(c)). a is result (as long as the the generation of voltage winding due field made up of the coil windings. rotating) is a laminated core moving in a magnetic field to The simple basic alternator just described used a magnet with two poles and a coil of wire with very few turns. In a practical alternator we want to develop more current, so THE VOLTAGE REGULATOR SIX-POLE MAGNET Most motorcycle 303 using silicon rectifiers are constructed diodes which act as one-way valves, permitting current flow in one direction and resisting Older opposite direction. which A act the same way 20-16) is current flow in the use selenium plates, as a diode. single diode inserted in cuit (Figure all rectifiers one lead of an alternator cir- a simple rectifier: current will flow through the load during one half of the AC cycle and will cease during the next half. Since the system rectifies during only half the cycle, Many we call a half-wave rectifier. it motorcycles use half- wave rectifiers. possible to arrange a circuit with four or six diodes It is The to use the current during the entire alternator cycle. circuit called a bridge circuit, and the system is full-wave COIL ASSEMBLY A Figure 20-12. A six-pole alternator. (Honda Motor Co., Ltd.) poles and coils with When the upper positive + polarity, in Figure 20is at current flows from the bottom (nega- ) through diode D3, through the load, and tive) terminal then returns to the positive terminal through diode D2. turns. If the alternator is magnet and a six-pole equipped with a six-pole rotating soft iron frame, as shown Figure in 20-12, the induced current will reverse every 60 degrees, and a More cycle will be completed every full current is 120 degrees. With reversal of current through the the terminals), diodes ity at DC and more motorcycle alternator can be constructed with any It is common practice to use one set of coils to generate ignition current and another set to generate lighting current, or the second half of the AC THE VOLTAGE REGULATOR one set of coils to generate the The voltage developed by an alternator speed of the rotor increases. The reason ship is stator in the alternator in a shorter must be developed additional coils for nighttime operation with lights on. charge the battery and power two basic alternator consists of is set a rotating parts: of stationary coils. The rotating magnet usually driven directly off the end of the crankshaft; the stationary coils are next to the rotating magnet. used in some alternators. A mounted (How control charging system voltage the field coil is position in field coil (Figure 20-13) is used is On increases as the for this relation- from the rotor cut across the that the lines of force windings Sufficient voltage assembly conducting cycle. current needed for daytime operation with lights off and The start current continues to pass through the load during frequently. even number of poles. magnet and a (change of polar- coil Dl and D4 generated because there are a greater num- ber of generating coils in operation and the magnetic lines of force are cut A shown is terminal of the alternator coil 17. many more called a rectifier. bridge circuit with four diodes ( we use magnets with more is the other hand, would increase if all unlimited at period of time. low speeds to the electrical accessories. at high speeds, this voltage to a point that the battery would be over- charged and the accessories damaged. The function of the charging system voltage regulator is therefore to limit the alternator voltage to a safe value. to described in a subse- Voltage regulation and the battery quent section.) The alternator can be constructed with the rotating mag- net at the center of the coil assemblies or, conversely, with the coil assemblies at the center of the rotating (Figure 20-14). The effect is the same either magnet In order for the voltage regulator to protect the battery accessories, is in THE RECTIFIER As mentioned above, ing current the alternator produces only alternatdirect 20-15) that converts alternating current (AC) installed in the circuit nator and the battery. to direct cur- between the alter- and limit the The voltage regulator, then, The battery voltage number of things, such as the bat- affected by the battery. turn affected When and the battery can only be charged by (DC) must be is by a tery's charging voltage, state of charge, current. Consequently, a device called a rectifier (Figure rent must sense the battery voltage and alternator voltage accordingly. senses and way. it the battery is voltage measured across the battery charging voltage. voltage which mainly is is the One component is called the battery of the battery charging counter-electromotive force, the voltage that by and temperature. being charged by the alternator, the chemical is means. battery charging voltage and or CEMF, produced within the battery is The CEMF the voltage opposes the which the bat- 304 UNIT 20: Battery and Charging System Operation and Servicing STATIONARY COIL Figure 20-13. Alternator componerits, (Yamaha Motor Corp. U.S.A.) THE VOLTAGE REGULATOR STATIONARY COIL ASSEMBLY GRAPH OF AC CURRENT ':- LOAD PULSED DC ROTATING MAGNET <5-^/, ROTATING MAGNET (+) I- LOAD f^ DIODE RECTIFIER (-) z::^ \^ y No current flow thru diode during this portion of cycle. (-) 'syJ -c^ STATIONARY COILS LOAD DIODE RECTIFIER Figure 20-14. Two stationary coil arrangements. (Honda Motor Co. Ltd.) (+) Figure 20-16. wave A single diode provides half- rectification. (Kawasaki Motors Corp. U.S.A.) SELENIUM HALF WAVE RECTIFIER SILICON DIODE HALF-WAVE RECTIFIER SILICON DIODE FULL-WAVE RECTIFIER SELENIUM FULL WAVE RECTIFIER DC WAVEFORM A rectifier changes DC- (Honda Motor Co Ltd.) Figure 20-15. rent to . AC cur- Figure 20-17. A saki Motors Corp. full-wave US. A.) rectifier, (Kawa- 305 UNIT 306 and Charging System Operation and Servicing 20: Battery must overcome The voltage produced by the order to charge the tery charging voltage in battery. alternator, then, always be higher than the CEMF when the battery is being charged. The CEMF affected by is rate, As of charge. CEMF. When many factors, including the temperature, concentration of elec- trolyte, plate area in contact with the electrolyte, and state the state of charge increases, so does the the state of charge is low, the and the battery will accept a high charge of charge is The rate is low. tery CEMF, charging rate high, the state CEMF is voltage is CEMF rate; is when low the high and the charge of charge, through its effect on bat- often establishes the charging voltage and in a typical charging circuit. The other component making up resistance. One of the simplest voltage regulation devices state current limiter that is battery's charging state Solid-state current limiter must the voltage drop caused The used on many is the solid- motorcycles. This device uses a zener diode, which does not always completely block reverse current. will pass current level, when and even then exceeding that level. ing a zener diode is A reverse-biased zener diode voltage exceeds a predetermined it passes only the amount of current A solid-state current limiter contain- connected in the charging circuit in parallel with the battery to bleed off the excess current that would otherwise overcharge id-state current limiter is the battery at high rpm. shown A sol- in a charging circuit in Figure 20-18. the battery charging by the battery's internal internal resistance consists of the Mechanical voltage regulator normal resistance to current flow inherent in the connectors, con- Some motorcycles nector straps, welded connections, plate area in contact with a mechanical voltage regulator to control charging with the electrolyte, and electrical resistivity of the electrolyte, together with other factors, including sulfated or dis- charged plates. One of the more battery resistance is important factors affecting temperature, which has an effect on the electrical resistance or resistivity of the electrolyte. the temperature decreases, the resistance increases. As Conse- quently, a cold battery having a high resistance will be hard to charge. On the other hand, a hot battery charge. is easy to system voltage. An alternator with a field coil is shown in Figure 20-19. In this type of alternator, the rotating magnet is only temporarily magnetized, through interaction with the field coil from the battery mounted in the alternator. The current to the field coil determines the strength of the magnetic field and, in turn, the output of the alternator. The mechanical voltage regulator limits voltage by conamount of field current in the alternator. The more current that flows in the field winding, the stronger trolling the Figure 20-18. Charging system with solid-state current Co., Ltd.) use a field coil in their alternator along SOLID STATE CURRENT LIMITER limiter. (Honda Motor THE VOLTAGE REGULATOR ROTATING MAGNET rects field current through a resistance in 307 order to lower al- ternator output. Early designs of mechanical voltage regu- of contact points. All lators utilized a single set mechanical regulators sometimes referred The utilize model late double contact points and are to as double-contact voltage regulators. wound around regulator consists of a coil of wire an iron core. The winding is usually referred to as a shunt winding. The winding and core are assembled together onto a metal frame, to which a flat armature steel is at- The hinge bends move toward the core when it is tached by a temperature-sensitive hinge. to allow the armature to magnetically attracted by current flowing in shunt the winding. The hinge acts as a pivot point, and the magnetic STATIONARY COILS attraction opposed by an adjustable helically wound is spring expansion located on the other side of the pivot Two point. sets of contact points, an upper and a lower, are insulated electrically the armature Figure 20-19. An alternator with a (Honda Motor contacts field coll. With Co., Ltd.) is this from each other and mounted on assembly (Figure 20-20). A stationary set of located between the upper and lower contacts. may arrangement, the contact points be posi- tioned so that either (1) the lower set will be closed, (2) the upper set will be closed, or (3) both sets will be sepa- The spring tension holds rated. when the regulator unit is the lower contacts closed not operating. Current that enters the regulator is directed to the upper where a small part of the current contact, is fed into the shunt winding. Current flow through the shunt winding produces a magnetic field which tends to pull the hinged armature downward. The amount of pull on the armature depends upon the strength of the shunt winding field, which in turn depends upon the amount of system voltage OUTSIDE VIEW ARMATURE that CONTACT POINTS SHUNT WINDING is pushing current through the winding. current alone is rent flows across the closed ternator IT Any 3s:p INSIDE VIEW field, the more lines In turn, set and directly the field winding in the al- it is operating. time the system voltage is low, the current flows the stronger the more voltage is Since the field. very low, a maximal re- field current flows to the field winding, producing a strong magnetic of force there are that cut across the stationary winding, and the is cre- in the alternator and providing maximum alternator output for any given engine rpm. When the alternator output increases, the voltage in the system increases, causing the magnetic field of the regula- winding to increase as well. The magnetic pull at any given alterna- be decreased. If the field current then becomes strong enough decreased as the alternator speed increases, a balancing sion on the armature. Consequently, the hinged armature ated. If the field current is tor speed, the voltage will is upper contact When mature, and directly into the alternator field magnetic not energized by the battery, the alternator will pro- sistance in this circuit Figure 20-20. Mechanical voltage regula(Honda Motor Co., Ltd.) the rotating magnetic field. is through the upper contacts of the regulator, through the ar- tor. is is duce voltage when E battery high enough to cause the armature to be pulled down. Curinto the alternator field. a: When directed to the winding, the voltage effect decreased can be obtained, with the net result being a nearly constant voltage that is regulated by the voltage regulator. The voltage regulator shown in Figure 20-20 consists of a magnetically operated switch that at appropriate times di- tor shunt to overcome the spring ten- and the movable contact are pulled away from the upper contact. This relationship of position and the two contacts is between the armature often called the floating position because the movable contact does not touch either of the UNIT 308 20: Battery When fixed contacts. position, current flow resistor, which is and Charging System Operation and Servicing the is movable contact is in the floating directed through a circuit with a a device that is usually made of metallic caused by hold-down clamps that are too be replaced. Inspect the battery cables and terminals for breakage, wire or of a carbon composition which limits or resists current flow. Current flows through the resistor and then onto the alternator field. Since the resistor reduces current flow, the alternator field strength is also reduced, in turn reduc- When a large number of Under crystals rosion is heavy, the -battery hold-down to and lights down could mean may demand high alter- material off the plates. condition, this be sure the top of the battery causes the armature to vibrate between the upper contact across the foreign material, the rotor field diverted is through the resistor, lowering alternator output. The low- may be parts. If the cor- overcharging. Check it is A tight. loose hold- that the battery has vibrated the active shunt winding, magnetic pull, and armature spring tension with the contacts separated, for dirt or green Inspect the top of the battery for dirt or electrolyte. If the combination of and the floating position. This vibration occurs because, Look on the battery and the connecting electrical accessories system are turned on, the electrical nator output. loose connections, or corrosion. the battery ing alternator output. any of tight. If these conditions are in evidence, the battery will need to to is not clean, current might flow which would cause self-discharge when the motorcycle Check the battery not in operation. is the level of electrolyte in the battery by observing Most the fluid level through the case (Figure 20-21). have a bat- minimum and maximum line on the case. If level drops below the minimum level, fill the ered output in turn causes the magnetic pull created by the teries The spring tension then overcomes the magnetism, and the upper contacts reclose. The cycle is repeated as much as 50 times per second. any cell fluid cell with distilled water to the correct height. Check the shunt winding to decrease. When few gine rpm is of the electrical accessories are in use and en- more current through and creating a very strong magnetic regulator armature down the regulator armature to As which is does not month, or even more often in hot weather. not use tap water. interrupting alternator output. last With ground through the lower fixed a result, the alternator field circuit is momen- field starts to The Checking specific gravity pulls the a direct circuit through bypassed. Consequently, the alternator collapse, winding the shunt field against the lower contact. the lower contacts closed, there tarily Do high, the alternator output voltage tends to in- crease, pushing contact. battery once a interruption very long, however. The magnetic field of the shunt winding collapses, allowing the spring to pull the ar- Once the battery has passed a visual inspection, charge should be determined. charged, lead sulfate the negative plate, is and When the removed from both sulfuric acid is its cell state is the positive process, the water content of the electrolyte and the acid content of the electrolyte is is decreased, increased. Since sulfuric acid is heavier than water, the density of the electrolyte is increased. The result is that the movable contact vibrates once more between the floating position and the lower contact. Again, occurs as many as The specific gravity of the electrolyte FILLHERE 50 times per second. r >• V -« CHARGING SYSTEM SERVICING Charging system problems are usually evidenced by a battery that is undercharged or a battery that is overcharged. Always begin your troubleshooting of the charging system by inspecting and testing the battery because it is the part that is most subject to failure. If the battery tests out satisfactorily, you can begin a systematic check of the charging system, following the appropriate sections of the shop service manual. Visual inspection of the battery The first step in checking out the charging system spect the battery visually. Look as a cracked case or loose or Look for for obvious is to in- damage, such broken battery terminals. bulging on the sides of the case which may be and again formed. In the mature and movable contact away from the lower contact. this vibration of being 20-21. Checking (Yamaha Motor Corp. electrolyte Figure cell level. U.S.A.) CHARGING SYSTEM SERVICE ELECTROLYTE A hydrometer used Figure 20-22. specific gravity. battery in the is a I (Honda Motor to check Co., Ltd J measure of the density of the electrolyte relative to the density of water. Water has a specific grav- of 1.000. ity The cell's state gravity of its of charge electrolyte is indicated by the specific and can be checked with a hy- drometer (Figure 20-22). The hydrometer consists of a glass tube with a other squeeze bulb attached to one end. The open end of the hydrometer is inserted into the cell by way of the vent cap hole. As with an eyedropper, the bulb squeezed and released, suctioning electrolyte from is the cell into the glass tube. Inside the tube, a float shows the level of the electrolyte. The below the electrolyte too far FULL CHARGE device float will not sink level if the electrolyte has a high concentration of sulphuric acid. DISCHARGE Figure 20-23. The float rises or sinks depending upon the concentration of sulphuric acid. (Honda Motor Co.. Ltd.) However, if it r^ is composed primarily of water, the float will sink farther down below the level. This sinking occurs because plain water has a lower specific gravity, or is "thinner," than water mixed with sulphuric acid (Figure 20-23). The that ity float in the hydrometer has numbered graduations allow you to determine the level and the specific grav- of the electrolyte. Figure 20-24 shows scale. The specific gravity chemical action in the how must be high enough cell, to read the to charged cell in a \ promote but not too high, because ex- cessive acid content can shorten the life of the cell. HYDRO METER A ELECTROLYTE well- motorcycle battery should have a specific A specific gravity of 1.200 to gravity of 1.260 to 1.280. 1.260 indicates only a partial charge. If the specific gravity Figure 20-24. Read the scale by sighting eye level, (Honda Motor Co., Ltd.) at 309 UNIT 310 falls 20: Battery and Charging System Operation and Servicing below 1.200, the battery should be recharged as soon it should not be permitted to remain for a long as possible; time in a discharged state. Temperature also plays a role in the variation of the specific gravity of the electrolyte. Since accurate readings can be made only if the temperature is fixed at SOT, most hydrometers have a thermometer built into the side. Should the temperature the hydrometer must rise above or be recalibrated. fall below 80°F, The reason is be- cause, as the temperature increases, the density of the electrolyte and decreases its whereas the reverse is The general formula for specific gravity is reduced, true as the temperture decreases. making allowances for tempera- ture variation is the following. If the temperature is or below 80°F, add .004 above specific gravity for every 10° over Figure 20-26. Charging the battery. (Honda Motor Co.. Ltd.) 80°F, and subtract .004 specific gravity for every 10° un- der 80°F (Figure 20-25). Charging the battery "F CORRECTION If the battery is 160° +.032 + .030 150° 140° 130° + .028 110° 100° 90° battery to overheat + .022 motorcycle battery charger.) + .016 nect the battery charger positive cable to the battery posi- + .014 tive terminal; + .012 tery negative terminal (Figure 20-26). + .010 + .008 + .006 + .004 80° -.002 60° 50° Follow the directions for using the battery charger. Con- .018 +.002 70° high amperage could cause the and explode. Use only an approved motorcycle battery +.024 +.020 can be charged by a long it — the +.026 + 120° discharged, ride on the motorcycle or by a shop battery charger. (CAUTION: Do not use an automotive -type fast charger on a from each connect the charger negative cable to the batRemove the caps cell to prevent a buildup of pressure. Then set the charger to the lowest possible charging rate, turn the charger on, measure the specific gravity frequently during when charging, and stop the process charged. Discontinue charging if -.004 boils electrolyte out of the cells. -.006 as noted in Chapter charging is very explosive. -008 -010 -.012 2, the the battery is fully the battery overheats or (CAUTION: Remember, hydrogen gas given ojf during Do low flame or sparks around a not smoke or otherwise al- batten,- that is charging.) -.014 40° -.016 -018 30° 20° 10° -.020 -.022 A -.024 the alternator rectifier or regulator. There are -026 ent types of systems, and -.028 20-25. Hydrometer conversion chart. (U.S. Suzuki Motor Corp.) Figure Alternator rectifier/regulator testing charging system problem can be caused by a failure of dure. When all many have a different test differ- proce- troubleshooting or servicing a charging circuit, always use the specific procedures and testers found appropriate shop service manual. in the NAME DATE SECTION Job Sheet 20-1 MEASURE SPECIFIC GRAVITY OF BATTERY Before you begin: Read pp. Model Make of Motorcycle Time Finished Time Started Flat-rate Total Year Time Time Special Tools, Equipment, Parts, and Materials Hydrometer Battery References Manufacturer's Shop Manual Specifications Procedure eye protection when using a hydrometer.) 1. (SAFETY CAUTION: Always wear 2. Remove 3. Squeeze the bulb on the hydrometer and put the hydrometer 4. Slowly release the bulb 5. the cell caps Bend over to read the from the battery. until the hydrometer float rises and tip into the electrolyte in the first cell. floats freely. The float should not touch the tube anywhere. hydrometer. Hold the hydrometer up so that you can read it at eye level, but do not Read the scale of the hydrometer float at the level of the electrolyte. lift it out of the electrolyte (Figure 20-23). 6. Put the electrolyte back into the cell by slowly squeezing the bulb. 7. Repeat steps 2-6 for each of the cells. 311 8. Record the Cell specific gravity reading of each cell in the spaces provided below: 1 Cell 2 Cell 3 Cell 4 Cell 5 Cell 6 Instructor check 9. A So change temperature will change the specific gravity reading since acid expands with heat and shrinks with cold. in the specific gravity reading you obtain could be wrong at high or low temperatures. To avoid this problem, you need to adjust the specific gravity reading to the temperature. 10. To make the adjustment, mometer is built into the first check the temperature of the electrolyte with a thermometer. (In most cases, the ther- hydrometer.) Then chcciv the specific gravity with the hydrometer. Subtract .004 from the hydrometer reading for every 10 degrees of temperature below 80°F; add .004 to the reading for every 10 degrees above 80°F. 1 1 Example. If the reading is 1 .280 at 70T: 1.280 (hydrometer reading) - .004 (for 10 degrees of temperature) 1.276 The 12. true adjusted specific gravity is 1.276. Correct each of your readings for temperature, and record the corrected readings in the spaces provided below: Cell 1 Cell 2 Cell 3 Cell 4 Cell 5 Cell 6 Instructor check 13. Average your corrected readings and compare them with specifications. Indicate below the percentage of charge for the battery: percent charge. 14. All cells should have the will not pick same specific gravity. If there is more than a .050 difference between the up or hold a charge. Record the difference between the highest and lowest cell in the cells, the battery space below: difference Instructor check NOTES Instructor check 312 Date completed DISCUSSION TOPICS AND ACTIVITIES KEY TERMS 313 1. Alternator: an alternating current generator used to develop and power the components on the motorcycle. current to charge the battery electrical plates of different metals in a solution of acid; 5. Why 6. Explain the chemical operation of the battery during used to provide a source of stored electrical energy. how 3. 4. Battery: an electrochemical device consisting of alternate Capacity rating: a rating of 2. does it take six cells to make a 12-volt battery? discharge. long a battery can supply Explain the chemical operation of the battery during current; usually specified in ampere-hours. charging. Cell: a basic unit of the battery that is capable of develop- What ing about 2 volts. Current limiter: a solid-state device used to bleed off excessive current on a charging system that does not use a 9. 10. How is is Explain battery capacity? battery capacity determined? how the battery together to provide field coil. Electrolyte: a mixture of sulfuric acid and water used in a 11. What is and charging system work power for the electrical system. the purpose of the alternator? battery. Mechanical voltage regulator: a voltage regulator that uses magnetically controlled switches to control alternator Identify the parts of an alternator by writing their names in the spaces provided. output. Rectifier: a set of diodes or selenium plates that is used to convert the alternating current from the alternator into direct current. Specific gravity: a lyte in measure of the strength of the electro- a battery cell. Specific gravity test: a test of the specific gravity in the cells that uses a hydrometer to find out whether the bat- tery is charged. CHECKUP Describe the parts and operation of a simple battery Identify the parts of the battery by writing their cell. names in the spaces provided. 12. 13. 14. 15. 16. What is the purpose of the rectifier? 17. What is the purpose of the current limiter? 18. How does the mechanical voltage regulator regulate alternator output? 19. What does specific gravity tell you about a battery? DISCUSSION TOPICS AND ACTIVITIES 1. Use a hydrometer to test several shop batteries before and after charging. after 314 What happens to specific gravity charging? (Caution: Wear eye protection.) 2. Disassemble a shop alternator and see if you can lo- cate and identify all the parts. After identifying the parts, reassemble the alternator. M< lost late-model road motorcycles are equipped with an system. The large-displacement multicyl- electrical starting inder engines are difficult to kick start; the starting system allows the rider to use the energy stored in the battery to power motor a starter These same mo- to crank the engine. torcycles are also equipped with many accessory systems, such as headlights, turn signals, brake lights, and horns. In this unit, we describe the parts and operation of the starting common system and some accessory systems. JOB COMPETENCY OBJECTIVES When you be able finish reading Explain 1. and studying you should this unit, to: operating the principle of a basic STARTING AND ACCESSORY SYSTEMS starter motor. Describe the construction and operation of a starter 2. motor. Explain the operation of a starter motor drive mecha- 3. RING GEAR nism. Explain the operation of the headlight, 4. light taillight, stop- FLYWHEEL and turn signal accessory system. Describe the parts and operation of a motorcycle horn. 5. \j- THE STARTING SYSTEM The two basic electrical starting One cranks Figure 21-1. in systems in ..^a use are shown motor con- the engine with a motor connected directly gine with a motor the first type, the is to the crankshaft. In called the starter motor, as functions in that capacity only. In the second type, the tor is called the starter/ generator motor the starting is starter motor starter is functions as it is started. used on most larger motorcycles and is becoming the most generator because common The starting system. starter/ The used in the small-sized motorcycles. motor type it mo- time of engine startup and as a at the generator after the engine The so arranged that the starter pinion is STARTER/GENERATOR drives the flywheel ring gear with a high gear ratio, deliv- Figure 21-1. Two types of electric starting systems. (U.S. Suzuki Motor Corp.) ering a high torque for big-engine cranking. In the case of the starter/generator, however, the motor is directly cou- pled with the crankshaft without any reduction in gear ratio. The result Because of that the this limited ing used less The is starter and cranking power is relatively low. power, the starter/generator is be- less. motor system uses energy that is overrunning starter clutch that has engaged the engine crankshaft. Reduction gears are sometimes used between the starter starter a direct-current motor needed to crank the engine. requirements are relatively high, motor and the starter clutch to multiply the motor's torque. to transform the battery's electrical energy into the mechanical PINION STARTER nected to the flywheel ring gear; the other cranks the en- Basic principles of the motor Amperage so an electromagnetic The starter motor changes the electrical energy of the bat- mechanical energy to crank the engine. uses the switch and heavy-gauge electrical wire leads are used to tery into make interaction of magnetic fields to convert electric current motor. the connection When between the battery and the the starter motor is actuated, it starter drives an It into torque, or twisting force. 315 UNIT 316 and Accessory Systems 21: Starting 1 LINES OF \ FORCE FROM CONDUCTOR POLES OF C MAGNET CONDUCTOR 1 \ \\ I / I \ » \ \ M PUSH I ' I I / ^-LINESOF FORCE ROM MAGNET * Figure 21-2. Magnetic lines of force from magnet and conductor. (U.S. Suzuki Mo- i I Figure 21-3. Thie stronger field pushes the conductor to the left. (U.S. Suzuki Motor the Corp.) tor * Corp.) some of In Unit 19, the basic principles of magnetism were described. One of these, very important to motors, that is when a straight wire conductor is electric placed in magnet with current flowing through the wire, there will be two separate magnetic the magnetic field of a one produced by the magnet, and the one pro- fields: the duced by the current flow through the conductor (Figure 21-2). In the figure, the magnetic lines leave the north pole of one magnet and enter the south pole of the other. The di- between the two poles of the magnets downward. The current-carrying conductor produces a rection of the lines is magnetic field consisting of concentric circles around the The wire in the direction illustrated. netic field (a heavy concentration of magnetic right-hand side of the wire, and a (On lines) weak magnetic field (a magnetic lines) on the left-hand side of the sparsity of wire. magon the result is a strong the right-hand side of the wire the magnetic lines same are in the direction and consequently add together, In this basic motor, current flows from the battery through the pole piece windings to a brush and commutator bar, through the loop of wire to the other and brush, and then back to the battery. commutator bar The resulting mag- netic fields impart a turning or rotational force on the loop of wire. As commutator two brushes, so the cur- the wire loop turns one-half turn, the bars interchange positions with the rent through the wire loop is in the opposite direction. pole pieces, the rotational effect will still be in the lines are in the opposite direction and consequently tend to When there and a weak to move from left in is field The simple motor just described with only one loop and two commutator segments cannot develop much torque because, though the magnetic forces are strong of the coil is when one side, the the strong to the weak way between the poles. Therefore, in practice, motors with many coil loops must be used. As one loop comes into the given example. (Figure 21-3). magnetic field FIELD WINDING POLE PIECES conductor will tend field, or from right to The stronger the produced by the magnet and the higher the BRUSHES current flow in the conductor, the greater will be the force tending to this move principle torque in is the conductor how all starter is right to left. energy is Use of converted to motors. In a simplified starter wire from electrical motor (Figure 21-4), a loop of located between two iron pole pieces and is con- nected to two separate commutator segments or bars. Rid- commutator bars are two sliding conducts called brushes, which are connected to the battery and to the ing on the windings that are located over the pole pieces. leg close to a field pole, they drop to zero mid- a strong field on one side of a conductor on the other same counterclockwise direction (Figure 21^). whereas on the left-hand side of the wire the magnetic cancel each other out.) But since the wire loop has interchanged positions with the COMMUTATER SEGMENTS LOOP OF WIRE Figure 21-4. Simplified starter motor. (U.S. Suzuki Motor Corp.) THE STARTING SYSTEM play and rotates past a field pole, another immediately takes way, the turning motion place. In this its uniform and the torque that rather than fluctuating, as is generated would it if is made made is maintain contact with the armature as used. Since the brushes must direct full battery current into the armature, they must be constructed of a material that will provide good electrical contact. Accordingly, they are usually made from The brushes various alloys of copper. which may be attached either to the commutator end frame A or to the starter field and frame assembly. A starter 5. The motor shown is exploded view in rotating loops (coils) are of heavy-gauge in Figure 21- made from many The copper wire. insulated lengths coils field which the field coils (located in the field frame assembly) produce. The core is small spring attached to the holder pushes the brush into contact with the commutator. are mounted lengthwise on a laminated iron core which not only supports them, but strengthens and concentrates the magnetic are held in position over the commutator by brush holders, motor construction Starter spins to provide a constant path for current flow. constant, only a few loops were it 317 and laminated to reduce opposing voltages called eddy currents (CEMF). The ends of each coil are attached to com- Starter motor drive mechanisms In order to crank the engine, the starter drives a large gear called a ring gear (Figure 21-6) A on the flywheel attached the generation of small to the engine crankshaft. mutator segments. The complete rotating assembly of current-conducting coils and commutator, core, and shaft is starter motor, called the pinion gear, either meshes with and drives the flywheel ring gear directly or drives the ring gear through a chain. A reduction gear is sometimes used motor armature. The commutator segments are insulated from each other with an insulation material called mica. The segments themselves are made of a good conductor, usually copper. The hardened-steel shaft, which is pressed through the core starter laminations, supports the armature in the starter housing in called the and allows it to rotate. from the The magnetic field are insulated starter The armature loops and commutator shaft. the in motor is created inside the housing (sometimes called the field-and-frame as- The field-and-frame assembly consists of field windings assembled over iron pole shoes which are at- sembly). coil tached to the inside of a heavy iron frame. The iron frame and the pole shoes provide not only a place onto which the field coils can be assembled, but also a low-reluctance, or low-resistance path for the magnetic flux that by the field coil The field coil the starter protected by an insulation wrapping. The field coils and connected electrically to a terminal usually magnetic field, The field coils while the brushes slide over the ro- end housing, mounted starter or end to the motor frame. is enclosed by a separate The brushes are usually commutator end housing; the other end housing encloses the drive mechanism (to be explained later). Small motors may not require a separate housing on are mounted in holders directly over the ar- mature, with the brush springs holding the brushes in contact The large flywheel ring gear or sprocket and the much smaller starter pinion or sprocket (pinion gear) allow the motor to turn at much higher rpm than the engine order to develop the necessary cranking force. engine however, the When the motor must be quickly disengaged, or the starter motor would be driven to excessive rpm by the engine and would be seriously damaged. starts to run, starter The starter motor is disengaged by a device called the overrunning clutch which allows the starter motor to engage the engine's crankshaft only while the starter motor is operating under a load (cranking the engine). engine starts, its When the increased speed automatically disengages the starter motor. Cross-sectional views of an overrunning shown in Figure 21-7. The motor armature shaft drives the chain and its The clutch housing is attached to the engine crankshaft. The starter is engaged by locking the pinion or starter sprocket. sprocket to the clutch; disengagement is achieved by un- locking these parts. Spring-loaded rollers in the overrun- The rollers ride on ramps in the clutch housing. When extended, they wedge the pinion or sprocket hub tightly against the clutch housing. the When the rollers are retracted, pinion or sprocket hub and clutch housing are no longer locked together. During cranking, the sprocket drives the overrunning each end of the starter motor. The brushes to increase the ning clutch housing do the locking and unlocking. armature to deliver current from the battery. Each end of the between the pinion gear and the ring gear turning torque. clutch used with a chain drive system are located at the top rear of the starter housing. tating produced and pole shoe assembly are mounted to housing by large screws. The field windings are the brushes are create a is windings. small gear on the end of the with the armature. Current from the battery enters the brushes and then passes into the armature. The brushes clutch housing. rollers to The motion of the sprocket hub causes extend and lock into the clutch housing. the engine starts and rotates at higher rpm its rpm the When increases, the clutch housing than the sprocket or pinion. The rela- 318 UNIT 21 Starting and Accessory Systems : COMMUTATOR SEGMENTS MOTOR ARMATURE ASSEME FRONT END HOUSING POLE SHOES FIELD COIL WINDINGS IRON FRAME Figure 21-5. Starter motor. (Top: Corp. U.S.A.) Honda Motor Co., Ltd. Bottom: Yamaha Motor THE STARTING SYSTEM CRANKSHAFT RING GEAR PINION GEAR STARTER MOTOR Figure 21-6. Starter motor drive nism. (Honda Motor Co.. Ltd.) STARTER CLUTCH ALTERNATOR SHAFT, {A} CLUTCH ENGAGED ^i= (8) 1. CLUTCH DISENGAGED CLUTCH GEAR mecha- ALTERNATOR ROTOR 319 UNIT 21 Starting and Accessory Systems 320 : a plunger this force, is drawn and a mov- into the winding, on the other end of the plunger ing contact is pressed NORMAL CORRECTION REQUIRED against the fixed contacts, completing the circuit between spring relay and the terminal battery the starter A terminal. return used to ensure that the contacts open when the switched off. is is The COPPER SEGMENT system wiring consists of two separate but starting and the battery- related circuits: the starter control circuit to-starter-motor supply circuit. the starter button and the light The MICA INSULATION control circuit includes gauge wire, included Figure 21-10. Inspecting the starter motor commutator. (Honda Motor Co., Ltd.) in the wiring harness, that connects the button to the relay. The battery-to-starter-motor circuit consists of heavy-gauge ca- from battery ble to relay to starter. the higher current that tor with carries system COMMUTATOR when the button make sure that all to operate fails check the system to first wires and cables are attached. STARTING GROOVE is WITH of charge with a hydrometer. If the battery If state SEGMENTS^ at least pro- WRONG WAV it is charged, the next check at fault. Use two main contacts of the relay. the problem is a faulty relay. If problem is to is it engine still now The only cranks, much wear in the starter system motor brushes and commutator. You can inthem spect the carbon brushes and replace if they are worn of their displacement within the brush holders. Refer to the shop manual for service limits in weak or broken. Again, refer to the the to be sure that clean and that the copper segments are smooth. lation must be stick will not get be Rough filed not is insu- shown in Figure 21copper segments become worn, they above the mica insulation, and the brushes good contact. Mica undercutting can be formed with a thin saw blade or a small 11). Mica it slightly undercut, as Thus, when the 10. no longer entire starter motor. ACCESSORY file SYSTEIVIS IHeadlights Almost commutator surface some shop manuals. Faulty armatures in shop man- ual for spring tension service limits. Check over shown or field coils usually can be corrected only by replacing the terms of brush length. Check the brush springs and replace any you find that are Inc.) dures are parts that get to the limit Figure 21-11. Mica undercutting using a small saw or file. (Harley-Davidson Motors, does not crank, the the starter motor. are the starter MICA MUST BE CUT AWAY CLEAN BETWEEN SEGMENTS TO SEGMENTS bypass the a screwdriver to bridge the If the RIGHT WAY MICA MUST NOT BE LEFT WITH A THIN EDGE NEXT necessary, charge or replace the battery. relay to see if UNDERCUTTING MICA WITH PIECE OF HACKSAW BLADE FILE somewhat is completely discharged, the relay will If the battery is MICA IN CORNERED its duce an audible click as the plunger moves within the electromagnet. 3 The most frequent problem simply a discharged battery, so check the battery's less than mo- to internal resistance. system servicing If the starter is The heavy cable required to operate the starter minimal losses due Starter pushed, is per- (Figure 21- or irregular surfaces on copper segments can smooth. The use of sandpaper or emery cloth is recommended, as abrasive particles may become imin the commutator segments. Wipe the commutator motorcycles have a headlight which all on whenever the engine of headlight: styles is replaceable-bulb the is normally running. There are two basic and the unit sealed-beam unit (Figure 21-12). A cross-sectional view of a sealed-beam headlight as- sembly light is has shown its in Figure 21-13. The sealed-beam head- lens, reflector, and lighting filaments assem- bled permanently in a sealed unit. Hence, in a sealed-beam headlight bums when a filament out. the entire unit be replaced. Replacement of a sealed-beam light is must more expensive than bulbs, but the airtight seal prevents dust bedded and moisture from entering the headlight and reducing the clean before reassembly. efficiency of the reflector. You can also make continuity tests to determine whether a malfunction in the starter motor is due to short circuits or open circuits in the armature or field coils. Test proce- The purpose of the filament energy passing through ment emits it is to transform the electrical into light energy. Since the fila- light in all directions, a reflector is required to ACCESSORY SYSTEMS 321 REPLACEABLE BULB HEADLIGHT HORIZONTAL ADJUSTMENT SCREW PIVOT SCREW RIM- LENS Figure 21-12. Two types of headlight assemblies. (Honda Motor Co., Ltd.) toward the lens redirect the light rays The inside surface of the lens a suitable angle. light- segments whose edges are clearly visible from refracting the outside and make appear as it Each into rectangles. if the lens segment lens is beam of light is made to appear were ruled off concave, causing diverge as they pass through light rays to a broad at composed of many is it. In this way, on the road ahead. Most headlights provide for high and low beam. Dualbeam headlights contain two filaments with just enough difference in position to provide high and low beam angles through the lens. A rider to light either the high- or the The headlights SIDE VIEW handlebar-mounted switch enables the are mounted low-beam filaments. Figure 21-13. Cross-sectional to the headlight rim through pivot and horizontal adjustment screws to allow them done by loosening the headlight mounting bolts and is which pivots the headlight specific in its rim. a Co., ro- assembly up or down. Horizontal admade by turning a horizontal adjustment screw tating the headlight justment of Ltd.) aimed properly for good night vision. Vertical adjustment is view sealed-beam headlight. (Honda Motor to be Always follow RIDER the adjustment procedure in the shop service manual. Figure 21-14 shows one recommended procedure for ad- justing the headlight. Taillight and stoplight Most motorcycles use a street rear of the stop. The taillight motorcycle and includes a taillight One headlight and comes on when other filament is when light lights filament is wired which signals in parallel the headlight is on. ley , a with the The connected to a switch that completes the brakes are applied. Figure 21-14. Headlamp adjustment. (HarDavidson Motors Inc.) up the assembly (Figure 21-15) contains a two- filament bulb. circuit which its The brakelight filament gets its current through the rear brake stoplight switch (Figure 21-16). pedal is When the pulled The rear connected to the operating rod of the brake switch. nder depresses the brakes, the operating rod is down, and the metal tip of the rod completes a cir- 322 UNIT 21 Starting and Accessory Systems : cuit between the contacts, lighting the brake pedal is and ating rod, stoplight. When the released, an internal spring retracts the operits metal An breaking the circuit. the motorcycle tip withdrawn from contact, is adjusting nut mounts the switch to frame and turned to raise or lower the is switch, controlling the distance the brake pedal must pull the operating rod before the stoplight comes switch height should be adjusted so that there on. is The some brake pedal free travel and the stoplight comes on just before the brake takes effect. Turn signal lights -LENS Figure 21-15. Motor Co., Ltd.) Taillight assembly. some motorshown in Figfront and two Signal lights are used on the front and rear of (Honda cycles to signal turns. A turn signal circuit ure 21-17. There are four lights: TERMINALS on the rear. The two two on the on the lights left signal and the two on the right signal a right CONTACT When STRIP is a left turn, turn. the rider turns the turn signal switch on, current flows from the battery through a flasher unit to either the left OPERATING ROD INSULATOR or right turn signal lights, as determined by the posi- tion of the turn signal switch. opens and closes the circuit, The flasher unit repeatedly causing the turn signal lights to blink. The typical flasher uses a set of breaker points connected to a bimetallic circuit. A element to open and close the turn signal simplified flasher bimetallic element is is shown in Figure 21-18. The formed by attaching two types of PULSE GENERATOR WIRE STARTER CABLE REAR BRAKE LIGHT SWITCH GROUND CABLE Figure 21-16. Taillight switch carries current to Motor Co., Ltd.) system; brake ttie taillight. light (Honda ACCESSORY SYSTEMS RESONANCE DIAPHRAGM FRONT REAR INDICATOR Figure 21-17. Turn signal Motor Co.. Ltd.) FROM BATTERY 1 , circuit. (Honda 323 UNIT 21 Starting and Accessory Systems 324 : ® ® ® ® o @ BATTERY MAIN SWITCH d) (D FIXED CONTACT POINT MOVABLE CONTACT POINT CONTACT POINT d) INSULATOR RESONATOR (?) DIAPHRAGM IRON RING ELECTROMAGNET DIAPHRAGM SHAFT RETURN SPRING ADJUSTMENT SCREW CONTACT POINT HOLDER PUSH BUTTON PLATE SWITCH 1 Check to see that the bulb is not burnt out. 2. Check for a 3. Check to see that the battery is supplying 4. Check for a 5. Check for a faulty switch. is If the switch is fuse. power. broken wire. come If the lights battery blown on, but only very dimly, probably the low or there headlight resistance in the circuit. is beam does not operate turned on, check to see if when the hi-lo the bulb filament is burned out. Also, check the switch. KEY TERMS Brushes: the sliding contacts that deliver battery current into the rotating armature. Commutator: ture the contact surface on which the brushes on the starter motor arma- ride. Field winding: the part of the starter motor that creates a Figure 21-20. Cross-sectional horn. (Honda Motor Co., Ltd.) GOOD view of magnetic a Motor armature: by a magnetic BLOWN FUSE field. FUSE the part of the starter motor that is rotated field. Overrunning clutch drive: a starter motor drive mechanism an overrunning clutch to disconnect the drive that uses pinion from the flywheel ring gear. Pinion: the gear or sprocket driven by the starter motor that rotates the flywheel. Ring gear: the gear or sprocket formed by the teeth on the Figure 21-21. Motorcycle fuses. (Ford Motor Relay: a magnetic switch that controls the circuit between Whatever source of cuit, the a fuse blows, same amperage ing. difficulty there should be located before a it When outside of the flywheel. Co.) it might be with the new fuse is the starter cir- installed. Starter motor: an electric should be replaced with a fuse of rating, never with one of a higher motor and the battery. motor connected to the engine's crankshaft by a gear or chain system; used to crank the engine for starting. rat- Fuses are rated according to the amperage they can withstand. Generally, the longer the fuse, the higher the amperage fuse. A rating. "30," The rating (in for instance, and operates successfully at amps) means is marked on CHECKUP the that the fuse is rated 1 30 amperes. Troubleshooting accessory systems lights or a horn are completely inoperative, battery — is it indi- systems 2. very likely no current flowing from the 3. cates that the circuit are dead, there the battery is is broken somewhere. If all completely discharged or discon- nected. If the at all, switch make is on and a these checks: light or the moves in a magnetic horn does not work 4. 5. 6. names why field. Identify the parts of a simplified starter their When Explain the principle of magnetism that asserts a conductor motor by writing in the spaces provided. (See art on next page.) DISCUSSION TOPICS AND ACTIVITIES Identify the parts of a starter in the motor by writing their 325 names spaces provided. (See art on page 326.) 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 24. 18. does a flasher work to cause signal lights to flash? 19. 20. How 25. What is the purpose of the starter clutch? 21. What is 22. What are the 23. How is the purpose of the starter relay? two types of headlights? the brake light activated? overrunning How does a horn create sound? DISCUSSION TOPICS AND ACTIVITIES 1. 2. Disassemble a starter motor and identify Disassemble a relay, identify operation. its parts, all the parts. and explain its 326 ^^fter the engine develops its power, the power must be delivered to the rear wheel of the motorcycle. This delivery is the job of an assembly of parts called the drive train. The components of the drive train are shown in the sectional view of an engine in Figure 22-1 The power devel. oped by the engine enters the power through a train One of primary gears located in a primary case. mary gears is chain) the primary gears (or sprocket and to effect an increase of torque is speed into the drive train. The clutch and reduction of is used to connect (engage) and disconnect (disengage) the engine's from the drive transmission, of attached to the crankshaft, the other to the The purpose of clutch. set the pri- train. From the clutch, which provides power flows power into the the rider with a selection of match engine power output with motorcycle speed. The transmission delivers power to the final drive, which in turn delivers the power to the rear wheel through a chain and sprocket or shaft assembly. In different gear ratios to this unit, we begin sideration of the be able 1. finish reading still this unit, On you should and the engine work the motorcycle, the drive train team moving from to start the cycle a standstill up to road speed. The rear wheel of the motorcycle rotates to to rotate the tire is torque. ratio. gine, but the engine alone cannot develop and explain the operation of a pri- and explain the operation of a multi- engine was described. rpm inspect, and reassemble a multiplate clutch. developed by the en- enough torque It standstill. developed by a motorcycle was pointed out there that differ- ent engines describe different curves, but they are low engine rpm, torque ilar in that at Adjust the freeplay on a multiplate clutch. is motorcycle moving quickly from a to get the drive. Disassemble, Torque In Unit 6 the torque curve plate clutch. 5. as a drive the motorcycle; the twisting or turning effort needed Identify the parts 4. a force that tends to is Describe the relationship between torque and gear mary 3. and studying applying torque. Torque, then, produce rotation. to: Identify the parts 2. SERVICING the study of the drive train with a con- primary drive and clutch. JOB COMPETENCY OBJECTIVES When you PRIMARY DRIVE AND CLUTCH OPERATION AND up increases, torque increases range at enough which the engine air and fuel. At will is low. to a point all sim- As engine in the rpm have trouble "breathing in" this point the torque curve will be- gin to drop off. The drive GEARS (SPROCKETS) AND TORQUE The purpose of the drive train is rpm. the engine to the rear wheel and to help the engine by increasing its torque through a system of gears. Before examining the individual components of the drive train, however, let some of the basics of gears and torque. As we have learned, the burning of fuel takes place in where the pistons and connecting rods force the crankshaft to turn. This rotary unit of force is called torque. train is to We One of the main purposes of the power effort. For example, when you use a wrench to tighten a nut (Figure 22-2), you apply torque to tighten the nut. When the nut you may not be able to turn it anymore, even though you are still exerting an effort. In that case, you are is tight, works to at at low higher speeds while operating at low speeds so that the en- at, or near, portant job of the drive train is, overcome low torque its is best torque range. An im- torque multiplication, that multiplying the engine's low initial torque to get the motorcycle moving and to meet varying road conditions. train multiplies engine torque by means of either gears or sprockets and chain. Both of these operate in the same basic way. Two gears are each other) in shown connected together (in mesh with Figure 22-3. Both gears have the same num- same diameter, so that both turn same speed. The gear ratio is therefore 1:1. In Figure 22-4, there are also two gears in mesh, one with 12 teeth and the other with 24 teeth. The smaller gear will re- ber of teeth and are of the increase the torque developed by the engine. can define torque as a turning or twisting is gine can operate The drive us consider the engine's cylinder, train allows the engine to operate the motorcycle power of to get the It at the volve twice as fast as the larger gear. When the smaller gear drives, the gear ratio between the two thus is 24:12, 327 UNIT 22: Primary Drive and Clutch Operation and Servicing 328 TRANSMISSION PRIMARY CASE CLUTCH PRIMARY DRIVE GEARS Figure 22-1. Parts of the drive train, (U.S. two meshing which they turn. Notice in Figure 22-3 and 22^ that when the two gears are in mesh, they turn in opposite directions. If we want or 2:1. In general, the gear ratio between gears is the relative speeds, or rpm, at the direction of rotation to be the same, gears. Thus, if we shown 22-5, in the in Figure same we must use three place a gear between two gears, as we can get the outside gears to turn direction. In that case, the gear in the middle is Suzuki Motor Corp.) called an idler, i.e., When gear A is turns clockwise idler it is free to turn on an idler shaft. turned counterclockwise, the idler gear and drives gear B counterclockwise. The gear does not affect the gear ratio between gears A and B. Sprockets and chain are used instead of gears in motorcycle drive two gears in trains. many Sprockets and chain work just like mesh: the number of teeth on the two sprock- GEARS (SPROCKETS) AND TORQUE 329 IDLER OR FLOATING GEAR IDLER SHAFT Figure 22-5. An idler gear allows gears to in the sanne direction. (Chrysler Corp.) turn TORQUE SPROCKETS Figure 22-2. Torque is applied to a nut with a wrench. (Yamaha Motor Corp. U.S.A.) dji3&'^ CHAIN Figure 22-6. Sprockets and chain work like gears, except that the direction of rotation is the same. (U.S. Suzuki Motor Corp.) lift it, Figure 22-3. Meshing gears with a tio. (U.S. Army) 1:1 shown as in Figure 22-7 (top). With the lever placed shown, only half as ra- box as much would be required force is required to raise the by hand. For example, suppose that a lifting force of 200 pounds is required to raise the end of the box. With the lever arranged as shown, as to raise it downward push is needed on the lever do the same job. The farther out on the lever you put your hand (away from the pivoting point, or fulcrum), the only a 100-pound to downward push is required. However, the farther away the pivot point, the farther your hand must move downward to raise the box. The mechanical advantage of less the lever is fulcrum in We — the ratio between the two distances from the Figure 22-7, 2:1. can compare the mechanical advantage with the mechanical advantage in gears. a lever Figure 22-4. Meshing gears with a tio. (U.S. 2:1 the ra- first is determines a gear ratio between them. The only differ- ence the is that the same two sprockets, driven by a chain, direction, as shown in turn in Figure 22-6. to in- crease torque or to provide a mechanical advantage. have probably used a lever to raise a heavy object. is too heavy to be lifted If a You box by hand, a lever can be used to Similarly, tom)), the smaller gear will rotate twice for each revolution of the larger gear. In other words, the mechanical advantage between the Both gears and sprockets and chain can be used far as the other. meshed and one has twice as many other (as, for example, in Figure 22-7 (bot- gears are teeth as the ets of twice as far from the fulcrum as the other end. end moves twice as when two Army) levers in When one end two gears would be gear drove the smaller gear. larger gear, the If the 1 :2 when the larger smaller gear drove the mechanical advantage would be 2: 1 since would have to exert half the force over the smaller gear twice the distance. , UNIT 22: Primary Drive and Clutch Operation and Servicing 330 A used for strength and quiet operation. chain adjuster is used to take up any slack in the chain and to prevent excessive noise. CLUTCH The clutch positioned in the primary case between the is engine and the transmission (Figure 22-11). It rider to disengage or disconnect the flow of allows the power from The rider disconnects the when shifting the transmis- the engine into the transmission. engine from the transmission from one gear to the next. Most motorcycles use a type of clutch sion plate or multiple disc wet clutch. multiplate clutch The clutch steel plates is shown called a multi- exploded view of a Figure 22-12. in consists of a An number of friction discs and stacked alternately and held tightly together by springs under pressure. The are the drive friction discs The plates, the steel plates the driven plates. friction discs have radial tabs on their outer edges that interlock with vertical slots Figure 22-7. Gearing provides a mechanical advantage or torque multiplication. (U.S. Army) plates is The clutch hub or center with the gear ratio of the driving to the driven when larger gear, the speed is is is attached to the transmission input shaft and rides in the center of the clutch housing when assembled. The clutch housing put shaft, but turns freely. When is centered on the in- the clutch is engaged, the a small gear drives a engine crankshaft drives the primary drive crankshaft gear reduced, but the torque delivered through a set of splines. The crankshaft primary drive gear gear or sprocket. For example, by the larger gear steel with splines in the clutch hub. The amount of torque multiplication we get from two gears or two sprockets varies with the mechanical advantage that on the edge of the clutch housing. The have radial tabs on their inner edges that interlock in turn rotates the clutch increased. housing, the clutch housing drives the friction discs, the friction discs turn the steel plates be- PRIMARY DRIVE cause the springs force them together, the steel plates turn the clutch hub, The the first set of gears or sprockets in the drive train is called of a small gear or sprocket attached to the crankshaft and a large gear or sprocket attached to the clutch assembly. The components of housed inside the the primary drive and clutch are primary case. Figure 22-8 shows the re- lationship of the small crankshaft gear to the large clutch The ratio between the small crankshaft gear and the larger clutch gear ratio is is usually about 3:1 (Figure 22-9). This provides a torque increase for the engine and a speed reduction for the torque entering the drive train. In other words, the clutch gear the engine. is The engine achieve the best part of turning only one-third as fast as is its thus allowed to run fast to Most late-model motorcycles use a gear-type primary drive. Many older motorcycles, and some still made today, a chain-type shown in Figure 22-10. A chain-type drive small sprocket crankshaft and a large sprocket special A primary drive. wide chain with three is is is attached to the the clutch is trans- disengaged, the release mechanism move away from each lowing them to slip. With the two power cannot be transmitted through are covered with other, al- oil the clutch. The plates so that during the slipping they are do not overheat. The oil covering is the is called a wet clutch. The clutch is disengaged by removing the spring pressure from the friction discs and the steel plates. The parts of the clutch release mechanism are shown in exploded view in Figure 22-13 and in sectional view in Figure 22well lubricated and why 14. A the clutch push rod connected to the clutch linkage enters the center of the clutch assembly. crown push crown is is is A round pushing device attached to the end of the push rod. The positioned next to the pressure plate, which attached to the clutch springs. When moves the rider squeezes the clutch lever, the linkage crown pushes on The pressure plate then compresses the and moves them away from the clutch hub. With- the push rod inward so that the attached to the clutch. A the pressure plate. of links side by side is springs sets hub drives the sets of plates slipping, called a torque curve. finally, the clutch activated and the plates reason gear. use When primary drive (Figure 22-8). The primary drive con- sists and mission. CLUTCH CRANKSHAFT GEAR PRIMARY CASE CLUTCH GEAR Figure 22-8. A gear-type (U.S. Suzuki Motor Corp.) primary drive. 331 UNIT 22: Primary Drive and Clutch Operation and Servicing 332 Many clutch mechanisms use a screw-type release mechanism (Figure 22-15). The unit works like a bolt and nut. The inner part (the bolt) has external threads and is connected to a lever that When the clutch cable screw. The outer is attached to the clutch cable. pulled, the lever turns the inner is turns, it and part has internal threads like a nut attached to the clutch push rod. When is the inner screw pushes the outer section and push rod inward to release the clutch. Another popular release mechanism is and cam the ball plate (Figure 22-16). In this arrangement, three steel balls are placed between the dents on the clutch lower the clutch release plate. two center holes of the When clutch push rod. A roller pin flat and plates is jump clutch GEAR-DRIVEN PRIMARY DRIVE Figure 22-9. The small gear crankshaft works drives the larger clutch gear at a ratio of 3;1 (U.S. Suzuki is Motor Corp.) just the opposite at rest, the The typical clutch is disengaged. activated by a clutch lever on the handlebar. Squeezing the handle causes a cable that nected to the handle to move. The motion ferred through the cable to the primary case, is is con- then trans- where a link- age arrangement changes the pulling motion of the cable into a pushing motion to move the clutch push rod. Figure 22-10. Chain-type primary clutch is is disengaged. in On it, is, the so that the other hand, when excess of a certain rpm, the centrifu- gal force pushes the steel balls unit. and that the of a regular clutch. That clutch springs force the clutch apart to disengage the engine speed is plates disengaged. by and the clutch two and the clutch push rod so small motorcycles use an automatic clutch that out spring pressure, the clutch discs are not held together friction, turned by is out of the dents in portion of the clutch release plate and the the roller pin Some and connected to the clutch lever plate. This action separates the moves plate inserted through the the clutch lever plate the clutch cable, the steel balls between the is outward and away from the Then, as the balls move outward, they climb a slop- which in mm With an increase in engine speed, the clutch ing ramp, engaged. It pushes the clutch plates together. is completely will then disengage if engine speed drops. This type of clutch uses no clutch lever or release mechanism. drive. (Harley Davidson Motors, Inc.) PRIMARY DRIVE TROUBLESHOOTING AND SERVICING 333 TRANSMISSION INPUT SHAFT .,RIGHTCRANKCASE DRUM STOPPER PLATE DRUM STOPPER CLUTCH RIGHT CRANKCASE COVER PRIMARY COVER f\ Figure 22-11. Clutch. (Honda Motor Co., PRIMARY DRIVE TROUBLESHOOTING AND SERVICING Noises are the most frequent problem in the primary drive Abnormal gear whine or clunking noises coming out of the primary case area can signal a problem. Always begin your diagnosis by checking the lubricant level in the area. primary case. with the Ltd.) If necessary, fill recommended type of the case to the correct level lubricant. Gear-type primary drives rarely cause any problems. Chain-type primary drives may suffer from excessive chain wear, sprocket wear, or damage to the chain tensioner. If you hear abnormal primary drive noises from a bike with remove the primary case cover and inspect a chain system, 334 UNIT 22: Primary Drive and Clutch Operation and Servicing TRANSMISSION-^ "^ („ INPUT SHAFT(SPLINED) CLUTCH HOUSING PRIMARY DRIVE GEAR PRESSURE PLATE STEEL PLATE FRICTION DISCS SLOT SPLINE CLUTCH HUB CLUTCH SPRINGS Figure 22-12. Multiple clutch. (Honda Motor Co.. Ltd.) PUSH CROWN PRESSURE PLATE PUSHROD Figure 22-13. Parts of the clutch release mechanism. (Honda Motor Co., Ltd.) CLUTCH TROUBLESHOOTING AND SERVICING CLUTCH HOUSING 335 FRICTION DISC T CLUTCH SPRING RELEASE INNER PRESSURE PLATE PUSH CROWN CLUTCH HUB RELEASE OUTER STEEL PLATES Figure 22-15. Figure 22-14. Sectional view of a clutcli release mechanism. (Honda Motor Co., Ltd.) these parts. Check sioned improperly. for worn The shop A screw-type THRUST BALL parts or a chain that is ten- service manual is clutch release mechanism. (Yamaha Motor Corp. U.S.A.) your best guide for chain adjustment. CLUTCH TROUBLESHOOTING AND 0^ ROLLER SERVICING PIN may show up in several ways. The rider may have a problem engaging the clutch, or it may slip when it is engaged. There is an engagement problem when Clutch problems you release the clutch lever and the bike acts in gear. Slipping is evident when you like it is not CLUTCH RELEASE PLATE CABLE CONNECTION accelerate the bike CLUTCH LEVER PLATE and hear the engine rev up without any power going to the rear wheel. The most common problems ment or cause slipping are; Weak Figure 22-16. that can prevent engage- tional Bent or damaged push rod mechanism. and cam plate clutch (Mid America Voca- Curriculum Consortium) friction discs or steel plates lever. The most common problems can cause the Binding clutch plates and friction discs Warped clutch linkage) Worn The opposite problem is when the clutch will not disengage that is, when you cannot disconnect the engine from the transmission even though you have squeezed the clutch that clutch not to disengage are: Clutch out of adjustment (not enough free play in — ball or broken pressure springs Seized cable, push rod, or linkage Worn release A or distorted clutch plates or friction discs clutch release mechanism Stretched or misadjusted clutch cable Clutch out of adjustment (too linkage) much free play in clutch UNIT 22: Primary Drive and Clutch Operation and Servicing 336 Clutch adjustment The most common adjustment. A service job performed clutch linkage that is on a clutch an is out of adjustment can cause slipping, nonengagement, or failure to disengage. The clutch mechanism release wear on the clutch requires periodic lubrication and adjustment for proper operation, compensate to for plates. Most bikes have a clutch cable length adjustor and a mechanism adjustor. The cable length adjustor is used to take up slack from cable stretch and to provide sufclutch ficient free ADJUSTER play for proper clutch operation under various The operating conditions (Figure 22-17). nism adjustor clutch mecha- used to provide the correct amount of is clutch push rod LEVER PLAY Figure 22-18. Adjusting clutch free play. (Honda Motor Co., Ltd.) movement or " "throw" for proper disen- gagement. Normally, once the mechanism justed, the only adjustment required free play at the clutch is for is properly ad- maintenance of handle lever. is determined by the amount of movement you can feel at the clutch lever. As you move the lever, you will find that it moves easily at first and then has more resistance as it starts to work the release mechanism. The amount of free movement is compared Free play in the cable free with specifications to see if the clutch free plate should be adjusted. To adjust the free play, loosen the handle lever adjustor lock nut. Then turn the length adjustor either in or out until proper lever free play If the is cable's free play achieved (Figure 21-18). is way out of specifications, or if you have a problem with clutch operation, you should check the adjustment on the clutch release mechanism. This adjustment determines pushed in when how far the clutch the handlebar lever push rod is squeezed. Different is models use different adjustments. Some use a cable adjustor located near the primary case (Figure 22-19), while others use a screw in the primary case shortens the release 1. 2. LOCK NUT ADJUSTER Figure 22-19. Clutch cable adjustment at (Honda Motor Co., Ltd.) the primary case. which lengthens or mechanism (Figure 22-20). After loosening a lock nut, turn the screw in until you feel a slight resistance. When you do, all the play is out of ADJUSTING SCREW Figure 22-17. Clutch measured Co., Ltd.) cable at the clutch lever is Figure 22-20. Adjusting screw on primary (Honda Motor cover. (Mid American Vocational Curriculum free play Consortium) CLUTCH TROUBLESHOOTING AND SERVICING 337 bent section of welding rod, remove the friction discs and metal plates. Stack the plates as they are removed so that you clutches can be mechanism and Clean all them to Look a 22-21. Measuring clutch friction discs for wear. (Honda Motor Co.. Ltd.) nut or snap ring are removed. the friction discs over carefully because, of wear the most. Look all and compare mechanism. Then back the screw off a specified turns to set the clearance. it friction plates with calipers with shop service manual specifications new Clutch repair If a clutch problem cannot be cured with an adjustment, have to be disassembled and inspected, and the clutch will new parts will specific The have to be procedure first step in in the Always follow installed. that protects case before you remove the shop service manual. removing the clutch mary cover it. it; is taking off the pri- Drain the oil from the primary an oil drain plug on the there is bottom of the case. Once the clutch is exposed, there will be nuts or screws that hold the springs in place. After you remove the clutch springs, lift off the pressure plate, ex- posing the clutch plate. Using a hooked tool, such as a ^^^^L the have overheated. Check the tabs for wear. (Figure 22-21). If necessary, install a full set of the release all surfaces over any signs of discoloration or peeling; these are signs Measure the thickness of the number of and allow air dry. that the plates Figure large the clutch parts in cleaning solvent, parts, they usually for them in their original position. removed as a unit after the release will be able to replace Some Figure fieight. 22-23. Measuring clutchi (Honda Motor Co., Ltd.) spring discs. 33B UNIT 22: Primary Drive and Clutch Operation and Servicing CLUTCH DISC PIECES) (7 LIFTER PLATE BEARING CLUTCH CENTER CLUTCH HOUSING (CLUTCH OUTER) Figure 22-24. Install PRESSURE PLATE the friction discs and steel plates the clutch parts as the housing revolves. Finally, turn the spring adjuster that is closest to the high spots, and test for cover and the clutch is reassembled, install the primary order. fill (Honda Motor Co., Ltd.) the primary case with the recommended type of lubricant. Adjust the clutch release mechanism and the free play. rotation. When in properly. Then check the clutch to see whether it operates SECTION NAME Job Sheet DATE. 4. Loosen the clutch adjusting screw lock nut on the primary drive. Instructor check 5. Rotate the adjusting screw clockwise until you can feel a slight resistance. Rotating the screw in this direction decreases the free play. 6. Rotate the adjusting screw the specified turns counterclockwise (check the shop service manual) and tighten the lock nut. 7. Rotate the clutch cable adjusters at the primary side cover and the hand lever Counterclockwise until the proper cable free play is obtained. 8. As you make 9. Tighten the cable lock nuts 10. the adjustment, measure the at the free play with a rule and compare it with specifications. hand lever end and the primary cover end. Test the clutch for correct operation. It should engage and disengage properly. Instructor check . NOTES Date completed Instructor check 340 1 NAME SECTION Job Sheet DATE . I22I2 DISASSEMBLE, INSPECT, AND REASSEMBLE A CLUTCH Before you begin: Read pp. Time Finished Time Started Flat-rate Year Model Make of Motorcycle Total Time Time Special Tools, Equipment, Parts, and Materials Eye protection Calipers Feeler gauge Drain pan References Manufacturer's Shop Manual Specifications Look up the following specifications and write them in the spaces below: Friction disc thickness Steel plate warpage Clutch spring height Instructor check Procedure 1. Look up the procedure for clutch disassembly and reassembly in the shop service manual. Instructor check 2. Drain the 3. Remove oil from the primary case. the primary cover. 341 4. Remove the pressure plate mounting screws and the pressure springs. 5. Remove the pressure plate and the push crown. 6. Remove the clutch 7. Remove the clutch assembly 8. Remove the clutch hub, discs, 9. Separate the discs, plates, and clutch hub. hub retaining snap ring or large nut. from the transmission input shaft. and plates from the clutch housing. Instructor check 10. Inspect the friction discs for excessive 11. Measure the wear and overheating. friction disc lining thickness specifications. with a micrometer or caliper, and compare the value with service manual Are the discs worn acceptable Instructor check 12. 13. Inspect the clutch's steel plates for excessive wear and overheating. flat surface one at a time, insert a feeler gauge between the clutch plate and the surface check for warpage, and compare the results with service manual warpage allowances. Are the plates Place the clutch plates on a to warped 14. Measure manual 15. acceptable the free length of the pressure springs with a vernier caliper specifications. Coat the friction discs Are the springs worn and compare the measured value with service acceptable with the recommended type of oil, and assemble the discs and clutch plates onto the clutch hub. 16. Install the plate, disc, 17. Install the clutch and hub assembly into the clutch housing. assembly on the transmission input a large nut. If using a nut, tighten it shaft, and tighten the connection with a clutch hub snap ring or to the specified torque. push crown into the end of the transmission input 18. Install the 19. Install the pressure plate 20. Install the 21. Check shaft. onto the clutch hub, and tighten the connection with mounting screws and pressure springs. primary cover and fill the unit with the recommended type and amount of oil. the clutch for proper operation. Instructor check NOTES Date completed 342 Instructor check KEY TERMS KEY TERMS Multiplate clutch: a clutch that uses alternate plates of friction Clutch free play: the space in the clutch release mecha- nism, measured at the clutch hand lever, that is used to provide clearance on clutch engagement. mechanism used to relieve spring pressure on the clutch plates in order to disengage the clutch. Gear (sprocket) ratio: a ratio determined by the number of teeth on two gears in mesh or two sprockets connected by a chain. and steel pushed together by spring pressure when they are engaged. Primary drive: a delivers Clutch release mechanism: a screw-type or ball-and-camplate 343 set of gears or sprockets and chain that power from the engine to the clutch and pro- vides for a gear reduction. Torque: a rotary unit of force; a turning or twisting effort used to rotate the rear wheel of the motorcycle. 344 UNIT 22: Primary Drive and Ciutcli Operation and Servicing CHECKUP Identify the parts of the drive train in the 1. 2. 3. 4. 5. spaces provided. by writing their names CHECK UP Identify the parts of the names 6. 7. in the primary drive by writing their spaces provided. 345 346 UNIT 22: Primary Drive and Clutch Operation and Servicing Identify the parts of the multiplate clutch names in the spaces provided. by writing their 17. 18. 9. 19. 10. 20. 11. 12. DISCUSSION TOPICS AND ACTIVITIES 13. 1 14. 15. 16. Count the teeth on the gears of a shop engine primary drive. Calculate the gear ratio. 2. Disassemble clutch. and How many reassemble a shop multiplate of the parts can you identify? when I he motorcyle engine is efficient only A rpm. ing at fairly high transmission it is operat- necessary to keep is high enough rpm while it is being slow speeds. The transmission provides the rider the engine operating at ridden at with a selection of four, five, or six gear shifts that allow him or her to match the engine speed to riding conditions. Each shift provides a different gear ratio and results in a different amount of mechanical advantage between the engine and the rear wheel. The torque must be multiplied by the transmission and directed to the rear wheel to push the motorcycle down the road. A set of sprockets and chain or a shaft system called used the final drive is to deliver the torque we mission to the rear wheel. In this unit and operation of the transmission and from the TRANSMISSION AND FINAL DRIVES trans- describe the parts final drive. JOB COMPETENCY OBJECTIVES When you be able 1 finish reading and studying this unit, you should to: Using different-size gears on the input and output shafts Describe the parts of a transmission and trace the flow of power through 2. 3. final drive. and trace the power selected, is it. Clean, lubricate, and measure a final drive chain. 5. Adjust the tension and alignment of a drive final chain. a very large drop in when high gear there is rpm the rider selects at the output of (fourth, fifth, or sixth usually a straight connection through the transmission. There to-1 reduction 4. is the transmission; gear) Identify the parts of a shaft drive flow through When input and the drive-sprocket output. low gear, there and explain the operation of a chain Identify the parts and sprocket it. allows the rider to vary the gear ratio between the engine is always, however, a 3- provided by the primary gears. Transmission gear types There are several basic types of gears inside the transmission. The exploded view of a transmission in Figure 23-2 shows these different types. Those that can spin on their TRANSMISSION shaft are called idler gears. They have a bushing on their inside surface so that they can rotate freely as the shaft The transmission (Figure 23-1) cases behind the crankshaft. shafts, each with a set is It is gear that is can turn it parallel freely. One torque of the engine through the clutch. countershaft, or shaft, called the output shaft, lay shaft, delivers the engine's torque out to the final drive There is on the input a set of gears in mesh with a gear of gears represents gears remains on the output shaft. all and a set the input shaft Each Each in is pair of the time, so the transmission sometimes described as being of of these sets speed. a transmission meshed shaft Each gear on is constant mesh. There are four, five, or six different-size gears on each shaft, and a gear set for each shift or speed the transmission has. During operation, only one power from the engine set of gears to the rear the other gears spin freely on is used to transmit the wheel. their shafts. As we shall see, An idler gear attached to its is always in mesh with are machined gears. When a shaft. one of two ways: me- in chanically, as part of the shaft, or with splines. as part of the shaft, splines are cut we call When they them integral on the inside of the gear match splines on the outside of the input or output to shaft, the gears are called splined gears. sprocket (or shaft drive). gears on the output shaft. is Gears can be attached to a shaft supported on input shaft, driveshaft. or main shaft, variously called the shaft, receives the spins inside them. made up of two of gears. Each shaft each end in ball bearings so that The other located inside the engine in As already stated, the gears on the input shaft are always mesh with the gears on the output shaft. In all cases, one of the gears will be attached to the will shaft, and the other be freewheeling. In order to use or deliver torque we have through any gear set, gear to Locking and unlocking are done with its shaft. to lock the freewheeling gears called sliding gears, or sliders. How a sliding gear works sliding gear has a set of tabs may be side. A square or round shift fork (to in is on shown its Figure 23-3. The which shape, and a groove around one be explained to the transmission shifter in side called dogs, engages in detail later) attached this groove. The slider 347 348 UNIT 23: Transmission and Final Drives FINAL DRIVE SPROCKET INPUT SHAFT GEARS INPUT SHAFT ENGINE CASE PRIMARY CASE OUTPUT SHAFT GEARS CLUTCH Figure 23-1. Transmission. Motor Corp (U.S. Suzuki TRANSMISSION OUTPUT SHAFT 349 V %W^^ DOGS ON SLIDER GEAR (LEFT) SLIDE INTO SLOTS ON IDLER GEAR (RIGHT) GEARS SLIDER GEAR SHAFT INTEGRAL GEAR SPLINES shaft, its the SPLINED GEAR slider gear has to its dogs. with its companion gear on its moved a short distance along splines) until the dogs engage in its When the two gears are engaged, gear is in mesh with another gear the idler gear its is the opposite shaft. at Only one one time, or the whole transmission would be locked up. Remember when holes, or the slider moves to lock up the gear next are locked to each other and to it, that the to their shaft. Power flow it. is solidly shaft. Since the idler that does not shaft (sliding slots, other dogs in the freewheeling idler gear next to attached through the slider gear to It of gears can be locked to the shaft two gears can then be shaft to another through move only a small amount to enmove enough to get out of mesh gage set Figure 23-2. Types of transmission gears. (Honda Motor Co., Ltd.) power can flow from one two gears. The on IDLER GEAR Figure 23-3. Operation of a sliding gear: slider gear (left) is engaged in slots of idler gear (right). (Mid American Vocational Curriculum Consortium) INPUT already locked to We are now ready to describe the flows through a typical way transmission. torque or power The transmission (Figure 23-4) has an input shaft and an output shaft. Since UNIT 350 23: Transmission and Final Drives When each has five gears, the transmission has five speeds. Each gear on the input shaft is a different size and is in mesh with a different-size gear on the output shaft. In Figure that 23^, all none of the dogs are engaged. Since none of the wheeling gears are locked We free- no power to a slider, there is flow through the transmission. slider that transmission in second gear. the sliding gears are positioned so mecha- the rider shifts into third gear, the shift nism disengages the A is currently holding the slider is then moved to the As shown right to attach the third gear to the output shaft. in Figure 23-7, power which the third gear, now flows across the input shaft to Power attached to the input shaft. is call this shift position then flows into the output shaft third gear, which normally neutral. If the clutch is engaged, the input shaft turns but none of the gears on the output shaft are driven. through the slider to the output shaft. Again, since the gear When the rider shifts into low gear or first 23-5), the smallest gear on the input shaft gear shaft is usually the integral type. in is put shaft. the left, it mesh with A first and to the output As the bike picks torque. Notice, however, that this time there gear) on the out- reduction and increase, respectively, because there moved locked to first Power then flows across to these speed and increase As is moved to the left, it is is ence is slight reduction in and locks it it is moved to With both second gears now locked shown Power now flows When The power flow Figure 23-8. Since there across the speed and increase the motorcycle is — gear up power can flow across them. Again, since a small gear is turning a large gear, speed decreases and torque increases. and the enough that there is gear only a slight differis only a in torque. highway speed, to in the ation, fifth gear (Figure 23-9). fast is which in fourth of the two fourth gears, there shifts into the top moving ISTGEAR OUTPUT SHAFT in in the size to the shaft, it. shifts. engaging the freewheeling fourth to its shaft. splined to the output shaft. to the left At the same time, the sliding gear lock up the first gear is now moved to to the shaft. which was used unlock of a is less on the input across to the fourth gear on the output shaft, flows across the input shaft to the second gear, which the output shaft through the the rider shifts into fourth gear, a slider gear and locking less is input shaft to the slider into the input shaft fourth gear, and in torque. rider will shift into sec- The second gear of we go of a difference in gear sizes as shaft turning a large gear, there freewheeling until the slider next to smaller than the gear on the output gear on the input ond gear. The power flow through the transmission in second gear is shown in Figure 23-6. Power from the clutch splined to the shaft. is a reduction in speed and an increase in first is up speed, the is and then locked to the slider, (first is is there now is on the input shaft shaft, gear shaft. a large reduction in used. This gear of the output shaft sliding gear next to the and the two gears. Since a small gear is The the largest gear gear (Figure is freewheels but the rider example under considerAt is this point the bike no longer a need is for a gear reduction (beyond that provided by the primary gears final drive). Fifth SLIDER MOVES TO LEFT Figure 23-5. Power flow in first (low) gear. gear on the input shaft and out- TRANSMISSION 2ND GEAR INPUT SHAFT 2ND GEAR OUTPUT SHAFT Figure 23-6. Power flow SLIDER MOVES TO RIGHT Figure 23-7. Power flow in SLIDER MOVES TO LEFT second gear. 3RD GEAR OUTPUT SHAFT in third gear. 351 352 UNIT 23: Transmission and Final Drives INPUT SHAFT j TO LEFT I 4TH GEAR OUTPUT SHAFT Figure 23-8. Power flow in fourth gear. SLIDERMOVES TO RIGHT 5TH GEAR INPUT SHAFT 5TH GEAR OUTPUT SHAFT Figure 23-9. Power flow in fifth gear. FINAL DRIVES same put shaft are the input shaft moved is Thus, when the slider on the it engages the freewheel- size. to the right, ing fifth gear and locks it to the input shaft. This fifth gear then drives the fifth gear on the output shaft at a 1:1 ratio. Consequently, there no reduction is in speed or increase in Hard can be caused by damage or wear shifting completely, by low transmission lubricant level, by scored damaged or shaft splines, or by a binding jumps out of gear, worn dogs that do not worn or damaged shift linkage. transmission If the As has been discussed, ent gears ing by a A the transmission shifts into differ- by having sliding gears move inside it. This shift- A shift lever. mechanism shift required to transfer the is mechanism located inside the transmis- is sion directly over the gears (Figure 23-10) and con- is nected to the gear shift pedal on the outside of the trans- The mission. The slots along The in the its the The most common wear problem is shown drum the 23-14). There to move the slider drum to a gear shift to the sliders, camplate. shift groove for scoring, which by the rotates, the forks are slots moved few degrees of rotation and change gears. the forks, pedal shift to to rotary is it has to be ro- is the transmission shift fork. check the shift fork components, follow shop service manual exactly. As you always mesh with free-spinning gears. Also, round dogs match against round holes, square dogs against Be aware square holes. that double sliding gears need two free-spinning gears on the other shaft and that sliding gears or fixed gears usually alternate with free-spinning gears. connected to the Kickstarter The kickstarter assembly allows the rider to spin the engine over with his or her foot for starting. motion and turns the the transmission (Figure 23-15). engage the correct gear (Figure 23-12). mesh with one of the gears A Transmission problems generally gories: noise and poor shifting. sion can be caused either port the input fall into to the kickstart pedal teeth one of two cate- Noise inside the transmis- by worn-out bearings which sup- and output shafts or by worn gears. In order most transmissions, the engine must be disas- sembled and the cases much work means that your diagnosis. Many times a split. you should be very sure of This problem or engine noise mission problem. On is confused with a trans- the other hand, any time the engine disassembled for service, the transmission should be engine cases fit spindle turns. into teeth The housed inside on the input gear shaft or, A is in on some spindle attached splined to a drive ratchet that has is the rider kicks is on the starter pinion. down on the kickstarter pedal, the teeth of the drive ratchet are shaped to drive the starter pinion, which spins the engine through the As soon as the engine starts, the drive must be pushed out of mesh; otherwise the kick- transmission gears. ratchet starter pedal could swing around and injure the rider. The shape of the ratchet teeth on the starter pinion prevents it from driving the ratchet. The teeth are angled and can only drive in one direction, as shown in Figure 23-15. A kick spring returns the spindle to position after each kick start. in- FINAL DRIVES spected for wear. The transmission which When It starter pinion models, with the clutch primary gear. specific worn a sliders evidence of wear. The camplate changes Transmission troubleshooting and servicing the ei- loose on assemble the gears, remember that splined. integral, and fixed gears drum, which has the shift move Accordingly, the gear drum enough is is often a micrometer or caliper specifica- is tion for the thickness of the fork. Also, As you reassemble and a gear moved by up and down motion clutch probably has for chipped gear teeth. Check worn, broken, or chipped dogs (Figure 23-13). the procedure in your linkage and then to a camplate. to service is engage or shift the gears. Just a In order for the tated. problem Check each gear for in are outside surface in which pins from the forks When drum. enough mechanism positions of the forks are controlled sideways to shift engaged shift pedal, shift forks are ride. is The mechanism forks that are shift drum, a gear at all linkage or a shift pedal that shift consists of a set of gear parts of a gear shift Figure 23-11. broken the fully Hence, check the contact area of the fork for wear (Figure the transmission. shift drum or the shift shaft. outside motion of the rider's shift lever to motion inside The gear transmission that will not shift ther a accomplished by the rider's moving a foot-operated is shift camplates. usually caused by mechanism to the or shift mechanism, by a clutch not releasing shift forks torque. Shift 353 shafts can usually be lifted out have been split. when Always follow the shop manual procedure for disassembling and reas- sembly is to deliver the gear wheel. sembling the gears. Transmission parts should be cleaned spected for wear or for gears that As mentioned previously, in solvent and in- do not engage properly. the purpose of the final drive as- engine torque from the transmission to There are two types of final drive: the chain and sprocket, and the shaft. The chain and sprocket is the oldest and by far the most common type. 354 UNIT 23: Transmission and Final Drives SHIFT MECHANISM TRANSMISSION GEARS Figure 23-10. The gear shift mechanism is located above the gears \n the transmission. (U.S. Suzuki Motor Corp.) FINAL DRIVES SHIFT FORK 355 GEAR TEETH CHIPPED GEAR DOG TOOTH SHIFT FORK NORMAL BROKEN CAMPLATE CHIPPED WORN VIEW 2 CHECK FOR WEAR IN FORK GROOVE SLIDER Figure 23-13. Checking for gear wear. (Mid American Vocational Curriculum Consor- GEAR SHIFT PEDAL Figure 23-11. Components of a anism. (Honda Motor Co., Ltd.) SHIFT SHIFT shift tium) mech- DRUM LI Figure 23-14. Check shaft fork (Honda Motor Co., Ltd.) SHIFT PEDAL Figure 23-12. Operation of the nism. (Honda Motor shift for wear. mechaand the transmission Co., Ltd.) is in gear, the driving sprocket turns, driving the chain, which in turn drives the rear sprocket. is attached to the output The rear sprocket is attached to the rear wheel and moves up and down with the rear suspension. The flexible chain allows for this up-and-down movement. The front drive sprocket is much smaller than the rear attached sprocket, providing a final reduction in speed and increase Chain-and-sprocket drive A chain-and-sprocket final drive system 23-16. In this system, a sprocket is shown shaft of the transmission, a driven rear sprocket is in Figure hub (center) of the rear wheel, and a chain connects two sprockets together. When the engine is running torque to the rear wheel. The numbers of to the in the two sprockets, of course, determine the teeth on the final drive ratio. 356 UNIT 23: Transmission and Final Drives SPINDLE (ATTACHED TO KICKSTART PEDAL) STARTER PINION (MESHES WITH TRANSMISSION GEAR) SPRING COLLAR KICK SPRING TRANSMISSION Figure FRONT SPROCKET 23-15. A kick starter assembly. ('Honda Motor Co., REAR SPROCKET CHAIN Figure 23-16. Chain-and-sprocket final drive system. /.fd.j FINAL DRIVES 357 ROLLER "0"RING GREASE LINK <^^)^^ OUTER PLATE SPRING CLIP Figure 23-17. Roller chain construction. Harley Davidson Motors. (Left: Inc. Right: U.S. Suzuki Motor Corp.) CHAIN DIRECTION OF TRAVEL Figure 23-19. The closed end of the clip faces the direction of chain travel. (Yamaha Motor Corp. U.S.A.) MASTER LINK Figure 23-18. The master link allows the chain to be separated. (Yamaha Motor Corp. U.S.A.) The size (number of teeth) of the rear sprocket changed for different kinds of riding, such as dirt can be or street riding. The rear sprocket may be bolted or may be directly to the rear hub, WIDTH The damper is made from a flexible material which absorbs some of the shock of the final drive when the clutch is engaged and enit bolted to a rear hub damper. Figure 23-20. Chain size measurements. (Mid American Vocational Curriculum Consortium) gine torque reaches the rear wheel. The chain used in most applications is a roller-type The construction of a roller chain is shown in Figure 23-17. Inner and outer plates, held together by steel pins, chain. form chain links. Pins are attached to the outer plates, bushings to the inner plates; the pins of the bushings. Rollers which bushings the pin roll through the inside around the outside of the around the pins to form a bearing between and the sprocket In order to fit fit remove the chain from the motorcycle, it has a set of pins with a groove cut in their end. assembled, a clip link together. When fits the clip When the into the grooves to hold the is removed, the link can be When you the chain. sure that the closed end is install a clip, make facing the normal direction of chain rotation (Figure 23-19). If the chain does not have a master link, a chain-break- ing tool must be used to push one of the pins out of one of the outer plates. The same tool is then used to push the pin back into position for reassembling the chain. Chains are constructed teeth. must be separated. Most chains have a master link like the one shown in Figure 23-17 and 23-18. The master link link is removed from power in different sizes Chain the transmission requires. according to the sizes are most fre- quently specified by the diameter of the roller, the width between lines links, and the distance (pitch) between the center of the pins (Figure 23-20). Chains must always be replaced with chains of the same the size of the sprocket teeth. size and must also match UNIT 23: Transmission and 358 Final Drives TRANSMISSION OUTPUT SHAFT INAL SHAFT UNIVERSAL BEVEL GEAR JOINT YOKE PINION Figure 23-21. Shaft final drive assembly. (U.S. Suzuki Motor Corp.) Shaft drive tioned at an angle. The chain drive system and does an efficient job of transferring torque. Chains, however, have certain built-in disadvantages. For example, they are hard to lubricate and tend to pick up dirt and abrasives which is relatively simple accelerate their wear. Also, they are noisy and prone to de- veloping a certain amount of vibration. To avoid these problems, some of the larger road motorcycles have gone to a shaft drive assembly. A shaft drive REAR HUB GEAR assembly is shown in Figure 23-21. The sembly The universal move up and down to joint allows the drive as- as the rear The universal joint yoke is attached to a shaft called the which is enclosed and protected by a housing, delivers power to another short drive shaft or propeller shaft. This shaft, shaft called the pinion wheel. A pinion gear is shaft that is located at the rear attached to the second gear of the pinion shaft. In mesh with the pinion gear is a large bevel gear called As the pinion gear turns, it causes the ring transmission and clutch are essentially the same as in a the ring gear. chain drive assembly, except that the output shaft is attached to a bevel gear instead of a sprocket. When the out- gear to turn. Since the ring gear put shaft turns, the bevel gear turns, driving another bevel gear that is meshed with it. Power flows through these two wheel goes up and down on the suspension. wheel hub, it is attached to the rear then causes the rear wheel to turn. The num- ber of teeth on the pinion and ring gears provides a final drive gear ratio, just as the sprockets in a chain drive do. bevel gears to a short shaft called the final shaft. From the final shaft, power flows to a universal joint as- Final drive inspection and servicing sembly. The universal joint is basically a Y-shaped yoke whose prongs (the upper, forked part of the Y) are connected by a crossmember called a cross or spider which is itself shaped like an X. The yoke is free to move up and oil. down taminated with in relation to the cross, allowing torque to be trans- ferred through the universal joint when the yoke is posi- Shaft Drive Servicing The shaft drive assembly Since the system vicing is is is normally lubricated with gear fully enclosed, dirt; therefore, it does not get con- periodic inspection and ser- not normally required. Any required shaft drive FINAL DRIVES or inspection servicing should be done following 359 the shop service manual. specific instructions in the Chain-and-Sprocket Inspection and Servicing The chain-and-sprocket system exposed is to road dirt; hence, the system requires constant attention for lubrication, wear, and adjustment. One of the most important things a rider can do crease the service life of his or her chain is to keep to in- it clean and lubricated. The three main areas of the chain that re- between the pin and the bushing, between the bushing and the roller, and between the overlap- quire lubrication are The most important ping side plates. area pin and the bushing, because that area stressed part of the chain. Lubrication and the forces roller is is between the LUBRICANTS most heavily the between the bushing important to provide a cushion against the arise that is the as Figure 23-22. Spray lubricant is used to bricate a chain. (Honda Motor Co., Ltd.) chain engages a tooth on the lu- sprocket. Chain lubrication cannot be achieved by pouring the outside of the chain. Oil oil on the outside of the onto rollers no useful purpose because chains and sprockets will serve are designed so that the roller seats into the sprocket tooth- pocket without any rolling or sliding. Beyond the small amount of oil required to prevent rust, oil on the outside of a chain serves only to collect dirt and sand, which accelerate wear. For proper lubrication, oil must be present inside the working parts of the chain. In order to get inside to the must chain, the oil plates travel between the overlapping side and into the bushing/roller area. however, in that in A dilemma between the side plates and into the chain, whereas the internal chain if protected, To it make order for the lubricant to must be must be it components are arises, its way thin, to be properly thick. resolve the dilemma, manufacturers have produced a number of LUBRICATE special spray lubricants for motorcycle chains. Figure 23-23. Cleaning the chain. (Honda Motor Co., Ltd.) These chain lubricants contain solvents which thin them, allowing them to penetrate the working parts of the chain more easily. At the same time, however, after application, 23-22 shows for protection. Figure back lubricant being sprayed A on the chain. in Figure 23-24. Use the same tool to push the pin in for come contaminated. Therefore, must be cleaned and relubed on it will eventually be- for long life, the chain a regular basis. Spray-on cleaners are available for the purpose, or the chain removed and soaked 23). All the solvent in solvent or may be kerosene (Figure 23- must be removed before the chain is assembly. good time replacement Regardless of the type of lubricant, cation. is to check the chain for wear and possible when Chain wear is it is removed from the bike for lubri- measured by determining the percent As of elongation or stretch that has occurred. works, the pins and bushings wear, resulting the chain in stretching in each of the links of the chain. Chain wear is then determined by calculating how much stretch has occurred. Note that bowing a chain sideways is not an accurate method of estimating wear. lubricated. To remove the chain, master link. If the spring clip. it first tool to determine whether it has a does, use a small screwdriver to remove Then remove the outer plate and push the does not have a master push a link pin out of the side link out. If the chain removing shown enough the solvent evaporates, leaving the lubricant thick link, use a plate, as To measure the chain, the old lubricant. Then the floor. Starting at first clean it in solvent to lay the chain out flat remove on a bench or one end, push each of the chain links together and measure the overall length of the compressed chain. Next, holding one end of the chain and pulling on UNIT 23: Transmission and Final Drives 3fi0 WORN BENT TEETH BENT TEETH WEAR AREA WEAR AREA INSTALLING CHAIN REMOVING CHAIN Figure 23-24. Use a special chain remov- push out link pins to remove (Yamaha Motor Corp. U.S.A.) ing tool to chain. Figure 23-25. Checking (Yamaha Motor Corp. GOOD wear. U.S.A.) measure the overall stretched length. Then sub- the other, tract chain for the one measurement from the other, divide WORN TOOTH this differ- ence by the normal length of the chain (the number of links times the pitch), and multiply the result by 100. This figure is the percent elongation. sively worn when You can The chain is inspect the chain and sprockets visually without disassembling the chain. With the chain cycle, lift shown pulled in considered exces- the elongation approaches 3 percent. the chain away from Figure 23-25. away from A still on the motor- the rear wheel sprocket as chain is defective more than half the sprocket if it Figure 23-26. Comparison of a worn and good sprocket, (Yamaha Motor Corp. U.S.A. can be the length of A worn shorten Suzuki Motor Corp.) Detail: U.S. a link. drive sprocket the life may result in of the chain. abnormal noise and Accordingly, sprocket teeth for wear and deformation. Look check the the sprocket over for any of the problems shown in Figure 23-26 (top). Sprocket-and-chain wear can be caused by operating in excessively dirty conditions, or by improper tension, im- proper alignment, and poor lubrication. Anytime the chain has been removed and bing the chain at its is with specifications. about '/2 it determined by grab- longest span (between the two sprock- Generally, the free play should be to Vt of an inch. Chain tension installed, should be checked for tension and alignment. The amount of tension (tightness) a chain has ets) and moving it up and down (Figure 23-27). The amount of up-and-down movement is called /ree pl<^y- After measuring the free play, compare your measurements is adjusted by moving the rear wheel as- sembly with the rear sprocket back or forward. gated slot is provided for the rear axle (Figure 23-28). The the elongated slot rear axle shaft is An at the rear elon- frame held in position in by the rear axle nuts and the drive chain FINAL DRIVES Figure 23-27. Checking the chain Suzuki Motor Corp.) 361 for ten- sion, (U.S. ADJUSTING BOLT LOCKNUT DRIVE CHAIN ADJUSTING CORRECT (MEASUREMENTS EQUAL) Figure 23-29. Checking rear wheel alignment. (Mid American Vocational Curriculum Consortium) REFERENCE LINES Figure 23-28. Chain tension adjusting mechanism. (Mid American Vocational Curriculum Consortium) INCORRECT (MEASUREMENTS UNEQUAL) that the same marks are in alignment. Finally tighten the axle nut, the adjusting bolt locknuts, and the adjusting bolts. After adjusting chain tension, adjusting bolts (one on each sometimes provided at side). Reference lines are each axle to help you keep the wheel square to the frame as you make adjustments. To make an adjustment, loosen the rear axle nut, the ad- justing bolt locknuts, and the adjusting bolts. adjusting bolts in or out until proper free play Turn both is obtained. Both bolts should be turned an equal amount to maintain correct alignment; if reference marks are present, be sure you should check the alignment of the rear wheel. Use a tape measure to measure from the center of the rear axle to some point on the motorcycle frame, and then repeat the measurement on the Be careful to use the same point both times. If your measurements are not the same, the wheel is not other side. pointing straight and you will have to make an adjustment on one side of the axle to correct the alignment (Figure 23-29). NAME SECTION DATE 4. Remove the chain from the solvent and hang it up so the solvent will drain off. Allow the chain to air-dry long enough to get rid of all the solvent. 5. Wipe off both sprockets and inspect the teeth for wear. Are the sprockets: Worn Acceptable Instructor check on a 6. Lay 7. Compress 8. Subtract the shortened length from the stretched length. 9. The difference the chain flat the chain as in surface, stretch much it to its full measure length, and then as possible without bending or kinking your two measurements is the amount of stretch. it, its length with a measuring tape. and measure it again. Write your measurements below: Extended measurement Compressed measurement Difference (stretch) 10. Compare the Worn amount of stretch you found with specifications. Is the chain: Acceptable 11. Spray chain lubricant over the chain several times and then wipe off the excess. 12. Install the chain over the sprockets and assemble the master link. end toward the direction of Make sure that the clip is oriented correctly (closed travel). NOTES Date completed Instructor check 363 NAME SECTION Job Sheet DATE . 4. 5. Turn both adjusting bolts As you in or out until you get the proper free play. turn the adjusting bolts, be sure that marks should be in you turn them an equal amount to maintain correct alignment. The same alignment on both sides of the wheel. Instructor check 6. Tighten the axle nuts and the adjusting bolt locknuts. 7. Measure from the axle center 8. If line to a common both measurements are the same, the wheel aligned. reference point on both sides of the frame. is in alignment. If the measurements are different, the wheel is mis- Are your measurements: Same Different Instructor check 9. If necessary, reposition one or the other side of the axle for alignment and remeasuring. NOTES Date completed Instructor check 365 366 UNIT 23: Transmission and Final Drives CHECKUP KEY TERMS Chain-and-sprocket drive: a final drive system in which a sprocket attached to the transmission output shaft is con- Identify the parts of a transmission in the spaces provided: nected to a sproclcet at the rear wheel by a chain. Chain free play: the amount of slack in the chain; used to determine chain tension. final drive 2. Final drive: the components that deliver engine torque from the transmission to the rear wheel. Shaft drive: a final drive system in which torque to the rear 1. 3. 4. is directed 5. wheel through a drive shaft instead of a chain. 6. Transmission: a system of parallel shafts and gears used to 7. multiply engine torque to get the motorcycle moving. 8. by writing their names DISCUSSION TOPICS AND ACTIVITIES 9. 10. How are transmission gears attached to a sliaft? Why are fixed gears always in 367 mesh with freewheel- ing gears? 11. Explain how dogs work to lock a freewheeling gear to its shaft. Identify the parts of a gear shift their names in the mechanism by writing spaces provided. 12. 13. 14. 15. 16. 17. 18. Identify the parts of a chain by writing their names in the spaces provided. 19. 20. 21. 22. 23. 24. Identify the parts of a shaft drive by writing the spaces provided. (See art on page 368.) their names in DISCUSSION TOPICS AND ACTIVITIES 1. Use a disassembled shop transmission to trace the 25. flow of power through each transmission 26. the input shaft to simulate 27. 28. 29. 30. 2. power shift. Turn flow. Calculate the final gear ratio in each speed through a transmission considering primary drive, transmission gears, and final drive. 366 UNIT 23: Transmission and Final Drives u,'p to we have studied those components of which develop power and transfer it to the bike's rear wheel. These components would be useless if they were not held in the relationship necessary for them this point, the motorcycle to function as a unit. Holding them in that manner is the purpose of the motorcycle frame. Working with the frame to smooth out the ride and provide the rider with good conor handling trol linkages, springs, this unit, we the suspension system, a series of and hydraulic dampening devices. In is describe the components, operation, and ser- vicing of the frame and suspension system. FRAME AND SUSPENSION JOB COMPETENCY OBJECTIVES When you be able and studying finish reading this unit, you should to: Describe the parts and operation of the frame and 1. steering system. Identify the parts 2. and explain the operation of the front and rear suspension systems. pensive to manufacture. 3. Change 4. Disassemble, inspect, and reassemble a front fork. 5. Check a Check 6. front fork hydraulic oil. arm rear swing rear coil springs which is bolted to the frame, also adds structural support. The basic advantage of this type of frame is that it is inexAll larger motorcycles use a tubular frame (Figure 2). This type of frame is welded together to form the finished for wear. makes and shock absorbers. Some FRAME front in the correct relationship is to hold all the motorcycle parts so that the bike can operate as a complete unit. The engine power train and rear wheel must be held in position so that The power can be delivered The frame good handling be positioned so that they are comfortable. holds the front and rear wheels in line for and provides the brackets for tached to it, all is formed by the top main tube, tube, and center tube. (See Figure 24—2.) later) is The attached to a snort tube in front called the head tube. To these basic tubes, a number of smaller tubes and braces are fitted to form the final structure or assembly. must be at- Steering system One of tube, the most important parts of the frame which provides the mounting is the head for the steering system. and battery. The frame also must be able to support the weight of ponents and one or two riders, all down such as the fuel tank, seat, fenders, electrical parts, lights, oil tanks, ing the parts that The design to the and footpegs must rider's controls, handlebars, structure. of the main tubes of the tubular frame have steering system (to be described The purpose of the frame 24- a series of tubes for a very light, yet very strong frame. names. The basic structure road. made from all comsame time withstand- the motorcycle's at the the forces of the road or trail, such as bumps and potholes. The frame must be designed enough to support all the the necessary stresses, with just the right to very all but also as light as possible and amount of flexibility. The stampedframe (Figure 24-1) is used on many mopeds and small motorcycles. It is made from a structure that is There are two basic types of frame steel be not only strong necessary weight and absorb stamped or pressed from steel parts in use. and then welded to- gether. The stamped-steel frame provides and strength for very small the needed motorcycles. rigidity The engine. Figure 24-1. Small mopeus ano muiorcycles use a stamped-steel frame. (Batavus U.S.A.) 3b9 370 UNIT 24: Frame and Suspension TOP MAIN TUBE HEAD TUBE \.'--A-^ FRONT DOWN TUBE HANDLEBAR CLAMP TOP BRIDGE Figure The ADJUSTING NUT OUTER RACE OUTER RACE move front wheel is attached to the front forks, which are BALLBEARINGS An turn attached to the steering head assembly. ure 24—3. INNER RACE the front or right to guide the motorcycle. ploded view of the steering head assembly BALL BEARINGS INNER RACE left The in assembly. Co.. Ltd.) steering system allows the rider to wheel COVER- frame 24-2. Tubular (Honda Motor A Only the right fork is is clamped around both the head steering is shown ex- in Fig- shown. part called a fork leg holder, bridge is lower crown, or lower A forks. shaft called the attached to the lower bridge and passes through the frame head tube. Figure 24-^ shows the forks in relation to The each other and to the mounting components. steering head STEERING HEAD the forces of braking LOWER BRIDGE to turn. must be designed both and to support the end of the motorcycle. At the same time, To fulfull these requirements, to withstand weight of the front it it must be free has two sets of bearings, one at the bottom to support the weight and one top to absorb the forces of braking. at the The bearings either ball bearings or tapered roller bearings. other by roller or ball bearings that roll on the races to re- duce friction. steel to The The balls and races are made of very hard enable them to withstand the forces they encounter. steering-head-and-bearing through the frame head tube. WHEEL A of the steering Motor Corp. is is installed head in position. A top then installed which clamps around the top of the forks and provides a A assembly cover and an adjusting nut are installed to hold the steering bridge U.S.A.) are each end of the steering head are two races, separated from each RIGHT FORK Figure 24-3. Exploded view head assembly. (Yamaha On mount for the handlebar. clamp assembly is shown typical handlebar 24—5. The clamp assembly fits in Figure over the bar and holds it in FRAME Figure 24-4. Front (Honda Motor Co.. Ltd.) steering assembly. 371 UNIT 372 24: Frame and Suspension DAMPER BOLT DAMPER KNOB HANDLEBAR CLAMP TOP BRIDGE RUBBER CUSHIONS HANDLEBAR Figure 24-5. Handlebar-to-steering-bridge mount. (Honda Motor Co., Ltd.) Rubber cushions the top bridge. tween the clamps and the bridge from being the front fork felt in are sometimes used befrom to prevent vibrations the handlebar. or oscillations from the front wheel are If vibrations transferred to the handlebar, the rider will steering to keep the motorcycle going some type of dampening device ingly, effect of these vibrations. damper, shown in have to fight the used to lessen the is One common BRACKET Accord- straight. type of steering Figure 24-6. Sectional view a steering of damper assembly. (Honda Motor Co., Ltd.) Figure 24—6, consists of a set of friction located on the lower bridge and connected by a discs Some bracket to the frame. of the discs are attached to the bridge, and others are attached to the frame through the bracket. The vibration. A friction knob at between the discs prevents unwanted the top of the handlebar assembly is damper bolt which goes down to Turning the knob allows the rider to set attached to a long friction discs. dampening A -STEERING HEAD amounts of tension on the discs and thereby change ferent the the dif- effect. damper is used on many steering systems. This type of damper has two parts: a center shaft (Figure 24-7) attached to the lower bridge, and an outer body attached to the frame. The damper is filled with hydraulic hydraulic fluid and works like a shock absorber. That shaft propels hydraulic fluid in the passages, moving the shaft is, the center body through restricting back and forth, and thereby providing a dampening effect on the steering. LOWER BRIDGE Frame and steering dimensions The frame and make the steering system are designed together to the motorcycle easy for the rider to control. ber of common A num- terms are used to describe some of these design relationships. Some CENTER SHAFT HYDRAULIC DAMPER of these terms, together with shown in Figure 24—8. Ground clearance is the distance between the road and the lowest component in the middle of the motorcycle. It the relationships they denote, are is important that the weight of the motorcycle be as low good cornering. Otherwise, the motorcycle would be top heavy and difficult to control. On off-road as possible for OUTER BODY Figure 24-7. A hydraulic steering damper. (Yamaha Motor Corp. U.S.A.) FRAME 373 STEERING AXIS LINE VERTICAL AXLE LINE TRAIL Figure 24-8. Frame and steering relationships. (Kawasaki Motors Corp. U.S.A.) ground clearance must be very high so dirt bikes, the the motorcycle The distance between center of the rear axle the center of the front axle and called the wheelbase. is motorcycle has a wheelbase also reacts Small do with how lot to slower handling because is The which also length of the handles. it A long reacts less rapidly it to a shift in the rider's position. steering response. Larger, heavier road bikes Steering feel tion Trail have a longer is also affected by a design feature called the distance between the points of intersec- is of two lines with the plane surface of the ground. of the lines, called the steering axis, runs of the steering head to the ground. cal line down The other from the center of the front axle which the other point, contact point — i.e., the center trail a motorcycle has and the fork offset. is determined by two The rake is of the steering axis from the vertical; the offset the angle is the dis- tance that the fork tubes are placed forward of the steering axis. Frame and steering system servicing in the Thus, if the front the friction of the road wheel on the tire is deflected by a bump, contact point behind and tire wear can cause poor twisted or bent so that the wheels is and suspension components are not in the ship to each other, motorcycle handling rider will have a difficult proper relationis affected: the time controlling the bike. Normally, the only way a frame gets damaged result of a crash. If the frame is is as a bent, cracked, broken, or otherwise distorted by a crash, handling will suffer. Cracks to follow, or self- one side of the steering axis pushes the steering system handling. If the frame or breaks in the frame are relatively easy to find. After a center of the tire's road wheel a tendency Frame damage and The the steering axis road intersection point. This rela- correct. How much factors: the rake ahead of to the ground. the center of the tire contact point tionship gives the front to is One line is a verti- steering axis intersection point with the road lies trails once again directly behind bikes often have a short wheelbase for a quick wheelbase to provide a more stable feel on the highway. trail. is change than does a shorter wheelbase, which more quickly dirt the center of the contact point the steering axis. denotes the length of the motorcycle. to a steering that can clear obstacles. around until crash, check the welds for cracks, especially around the Chipped or peeling paint is an indication of all steering head. a possible problem. any cracks easy Wash to see. the frame thoroughly to make The frame can be inspected with magnetic or fluorescent crack detection equipment. Diagnosis and repair is normally done by experts adept use of this special equipment. in the UNIT 374 A 24: Frame and Suspension bent frame is a lot harder to diagnose than cracks. may small bend in the frame not be visible but can The only alter the cycle's handling. and correct kind of a problem this way sure to is to A still diagnose completely disas- semble the motorcycle and have the frame checked and, if necessary, corrected on the manufacturer's test fixture. The steering system requires periodic maintenance and a handling problem. The inspection, especially there if is head bearings are subject to damage from unex- steering pectedly high shock loadings, such as might be caused by accidents. In order to have head bearings smooth steering, the steering and lubrication. They cleaning require damage should be removed, cleaned, and checked for fore be- being coated generously with a heavy, waterproof grease such as lithium grease. Then they should be reas- sembled. When the steering head is disassembled, check for obvi- Look ous broken or crumbled ball bearings. the races and pits, or dull spots While the steering head steering stem on a it in position in the steering bottom end of the bridge. the reset solidly U.S.A.) head tube and on they are loose, the steering If Figure 24-9. The suspension lets the wheels bounce while preventing the bike from bouncing. (Kawasaki Motors Corp. surface. If flat you remove the bearing races, they must be and squarely balls. disassembled, check that the by placing straight is is for dimples in on the races and Thus, the cocked slightly, the steering will bind, torcycle can may be destroyed completely. The most important The wear and loss head reassembly part of steering the bearing adjustment, which, if fast and the bearings done properly, To of control. adjust side. The bearings must be loose enough so wheel will fall to either side when the bike enough so is to on a center that there is wheel back and at all, forth. If you are able same no back- try to pull the front to feel many minor While variations, they all op- same manner. Front suspension The front suspension system consists of a ing front forks (Figure 24—10). its axle, is The set of telescop- front wheel, through attached to the bottom end of the front forks. is attached to the other end through the steering TELESCOPtNG FRONT FORKS any movement the bearings are too loose. SUSPENSION The suspension system is a set of linkages, springs, and damping devices that are used to suspend or hold up the weight of the motorcycle and rider. The suspension system also connects the wheels to the frame. The most hydraulic important function of the suspension is to cushion the mo- from the bumps on the road. If the susjob, the wheels of the motorcycle can go torcycle and rider pension does its up and down as they cle's An roll over bumps without the motorcy- bouncing (Figure 24—9). often overlooked fact is that the tires (see Unit 26) are an important part of the suspension. The to sus- on the center for play, leave the motorcycle Then respectively. that the front The frame stand and grab both front forks. tires, tires. and rear suspensions and then and-forth play in them. To check support the front and rear pension systems have stand with the front wheel off the ground. At the time, they must be tight bounce up and down on the erate in essentially the elasticity. can be compressed, and the mo- typical motorcycle has front bearings, swing easily from side until the forks air in the tires will avoid the tighten the adjustment nut until the bearings bind, back off the nut is some with air under pressure and also have bearings will go out of adjustment quickly. If they are tires are filled Figure 24-10. The front suspension consists of a set of telescoping front forks. (U.S. Suzuki Motor Corp.) SUSPENSION 375 CAP J^ TOP BOLT — UPPER COVER -FORK COIL SPRING DUST COVER=> COIL SPRING- PISTON SLIDE- a -OUTER TUBE SLIDE INNER TUBE- INNER TUBE PISTON ORIFICE OUTERTUBE— FLUIDFigure 24-11. Exploded view of a telescop(Yamaha Motor Corp. U.S.A.) ing front fork. system. Each fork is constructed from an inner and outer tube that can telescope in on each other, allowing the forks wheel moves up and to get longer or shorter as the front Figure 24-12. Front fork assembly, (Kawasaki Motors Corp. U.S.A.) down. Basically, each fork is a tubular hydraulic damper or shock absorber with an internal or external spring to support the motorcycle. The forks work to support the cycle without transferring road shocks to it and the An exploded view is shown 11, in Figure 24-12. of a front fork and a sectional view is shown motor- in rider. Figure 24- The front fork to the frame) With is divided into the inner tube (connected and the outer tube (connected to the wheel). the inner tube inserted into the outer tube, both tubes move up and down in a sliding motion. A slide located top of the outer tube provides the sliding surface. The on ver- UNIT 376 tical 24: Frame and Suspension motion of the tubes and by is CHAMBER FORK SLIDE SPRING HOLDER INNER TUBE •SPRING controlled by a long coil spring fluid inside the unit. When the wheels hit a bump, the springs mounted between the inner and outer tubes compress, allowing the PISTON forks to move upward to follow the contour of the bump. The compression of the springs and telescoping of the forks prevent the impact of the bump from moving up the frame. As the wheel reaches the top of the bump and UPPER VOLUME CYLINDER VALVE BODY VALVE SPRING .ONEWAY VALVE VALVE ASSY VALVE PLATE starts back down, the bike continues upward for an instant and then also starts coming down. When level surface, stops falling, but the motorcycle continues it the tire reaches the down, past the normal position, until the increased pressure of the compressed springs can overcome the downward force of the bike. Then the bike moves back upward towards If the its normal position. forks had only coil springs, the motorcycle continue to bounce up and springs MAIN PISTON would be down until the energy dissipated. But the hydraulic would CIRCLIP in the dampers in LOWER VOLUME the forks slow the extension speed of the springs so that they cannot push the motorcycle up beyond When sition. its normal po- the spring tries to extend after being com- damping unit resists the attempt. A sectional view of the damper parts inside a fork is shown in Figure 24-13. Inside the damper is a piston in a cylinder. The piston pushes oil back and forth through tiny orifices (holes) and one-way valves. The oil's resistance to pressed, the flowing through the orifices and valves that is COMPRESSION STOP the resistance slows the extension of the spring. O Compression When the fork telescopes, the slide over the inner tube, forcing in the cylinder, valve plate, oil The oil flow holes and valve body. Since these parts are all fastened to the inner tube, they ary relative to the slide. Figure 24-13. Fork hydraulic dampening system. (Kawasaki Motors Corp. U.S.A.) moves up and down through the PRINCIPAL OIL FLOW EXTENSION PRINCIPAL OIL FLOW COMPRESSION OIL FLOW HOLES oil is remain station- then trapped because the hand, the volume increases during rebound because the moves out of ner tube the slide. The piston seals against the inside of the inner tube, and the the bottom of the cylinder are large inner tube seals against the inside of the fork slide. to the moves from volume to the upper volume as the fork slide rises, and from the upper to the lower volume as the fork slide drops. The two volumes are sepaThe rated A oil by the valve the lower parts. one-way valve assembly is located in the end of the which helps prevent any resistance during compression. As the slide moves up on the inner tube, oil moves from the lower volume to the upper by flowing inner tube spring chamber during pression. The spring to allow free oil flow compression stroke, the com- carries the load during compression. Rebound During the rebound stroke, ume oil flows from the upper vol- as the size of the to the lower, upper volume de- creases. The valve shuts against the valve plate immediately because now the oil pressure close against the valve plate because of the oil pressure. hole at the top of the cylinder. this time, the oil is also allowed to move from The it. The oil in oil is helping the spring can get out only through the tiny the spring chamber flows easily oil volume through the center of the cylinder to the spring chamber above the piston. This translation is necessary because the total volume of the upper and lower vol- umes decreases during the compression stroke of the fork. top of the cylinder, determines the The reason for the decrease in volume is because tube takes up more room inside the fork slide. On the inner the forks will the other small into the is lower volume. The rebound oil and flow speed, which controlled by the size of the small oil flow holes oil flow down through the cylinder, out the large oil flow holes at the bottom, the lower in- flow holes near thereby aiding in preventing the unit from resisting through the valve. The tiny spring cannot hold the valve During oil amount of at the resistance have to being extended by the springs. If the at the top of the cylinder were even flow holes SUSPENSION The dampen SHOCK AND SPRING ASSEMBLY shock rear absorber twin-shock or 377 absorbers The shown in Figure 24-17. The rear shock absorbers or dampers have an arrangement of one-way valves and small oil flow orifices that give them the desired damping characteristics. spring action just as the front fork units do. shock or damper On most located inside the coil spring, as is motorcycles, the rear units cannot be disassem- bled or repaired, so how tion of Most REAR SWING ARM shall not present a detailed descrip- rear springs have a provision for changing the spring rate. This spring adjuster Figure 24-14. Swing arm rear suspension system. (Harley Davidson Motors. Inc.) smaller, there we they work. The bottom of whose position would be more rebound damping (controllby a hydraulic piston assembly). ing spring oscillation is shown Like the front wheel, the rear wheel must be allowed to the frame. The low slot in you to select a high The slots increase or for the spring seat. it by coil springs wheel rear is and hydraulic shock absorbers. The The attached to the end of the swing arm. name from the fact that it allows the wheel to swing up and down (Figure 24—14). The swing arm is mounted to the rear of the frame on a set of bearings or bushings so that up-and-down movement unit gets its is possible. pension is An exploded view of a typical swing arm sus- shown in Figure 24-15. A pivot A through the frame and the swing arm tube. fits into the shaft fits long bushing swing arm tube and supports the center of the swing arm. Smaller frame bushings support the pivot shaft in the frame. When the rear wheel Movement of in an arm is controlled by one or and one or two shock absorber 24-15 each side of the swing arm has a middle of the coil spring sign is is sign, in is coil spring, and such as the wheelbase and the steering the motorcycle, trail. If the tension motorcycle has a chain-type is also affected (Figure 24-18). in is called a monoshock A de- is monoshock at- sys- The chain tightens and loosens as the dis- rear spring or springs The and shocks are similar, in springs support the weight of motorcycle and are on the outside of the suspension This arrangement allows the use of a longer spring than would otherwise be possible. The external spring has unit. another advantage in that it Heating of the spring is traction and expansion. which is why travel is as much a correct chain tension problem impor- is cooled by the surrounding caused by the energy of conis Suspension system servicing Front or rear suspension problems stiff may show up crash, the front forks and rear trailing for breaks, cracks, or the rear swing as poor or soft suspension action. After a arm must be checked and bends. Damage to the front forks arm can make the bike difficuh to steer and control. The same techniques as are used to locate a Figure 24-16. principle, to the forks. chain between the two sprockets changes with wheel tance handling, or too which one large spring and shock absorber shown The final drive, the by the action of the swing arm in a shock absorber. This de- tached to the center of the swing arm. tem the wheels rise and however, they change the other basic dimensions of two units. In Figure called a twin-shock design. Other motorcycles use what air. fall, tant. arc. the swing As over without disturbing the rider. Too much suspension wheel moves move up and down go over bumps, the greater the suspension travel, the larger a bump or the deeper a hole that the wheel can travel to little, mounted relative to the rest of the motorcycle. Because the wheels must as too is You may a passenger. the distance that the front or rear is move up and down wheels can travel. coil springs the Suspension travel to rear the in the vertical swing arm which be. travel frame on bushings becomes the pivot point, and the direction, the part of the the moves Suspension may you normally carry if rear suspension system consists of a swing arm assembly controlled adjuster, absorber. Turning the adjuster allows or want to change tension move up and down independently of Figure 24—17. controlled by a spring seat on the shock is decrease the spring tension, as the case Rear suspension in on the spring the coil spring sits frame problem will work for suspension system components. Worn worn hydraulic components can coil springs or cause the suspension to to fail wheels properly. The bike will the parts are binding, hydraulic parts lost: fail, the bike will it the may control the start to feel start to feel damping motorcycle too soft, or, too stiff. if When effect of the springs is begin to bounce excessively after a UNIT 378 24: Frame and Suspension UPPER SHOCK MOUNT PIVOT SHAFT Figure 24-15. Rear swing arm assembly. (Yamaha Motor Corp bump. have If you experience any of these problems, you will to service the front or rear suspension. If Front Fork Servicing Sometimes of hydraulic front fork oil in the The a change fluid can get Or worn change of To change bolt (Figure dirt, seals you have poor try a problems can be cured by hydraulic dampers. contaminated with torn. USA) especially if the fork dust boot gets can allow the hydraulic front fork action, a good oil to first escape. step is to fluid. the fluid, place a drain pan under the drain 24-19) on one of the forks. Then remove the SUSPENSION MONO SHOCK AND SPRING 379 Loosen the pinch bolts on the steering stem and bridge, and remove the forks. and clips, oil Remove the fork tube caps, spring drain screws. (Refer to Figure 24-19.) Drain You can then hand pump remove any remaining fluid (Figure 24-21). Remove the Allen bolt from the bottom of the fork as- the fork oil as described earlier. the fork to sembly, and pull the inner tube out of the outer tube. To remove move the set the fork seal, Then pry out with a screwdriver. not to cover and pull off dust first re- ring or circlip over oil seal (Figure 24-22) damage A the fork tube. The escape from the oil seal, being careful bad a oil seal is common wear out frequently, allow- front fork problem. seals ing fluid to the fork. Pull the remaining parts out of the tube. Clean Examine each part for evidence of damage or wear. of the inner tube the straightness. tube If the should be replaced. fork You can check ing the tube over a for any bends by for surface. If the tube flat and scratches scratched severely or bent, is where, you should be able to see Check and allow them the parts in cleaning solvent all to dry. Inspect hop it the outer tube for dents. If as it it roll- bent any- is rolls. any dent in the outer "hang up" during operation, tube causes the inner tube to the outer tube should be replaced. Check SWING ARM PIVOT SWING ARM Figure 24-16. The mono shock system uses one shock and coil spring, (U.S. Suzuki Motor Corp.) fill plug at the top of the fork and the drain plug bottom of the fork. Allow the To push any remaining oil mended type and amount of plug. Finally, replace the for the other fork down on and use a funnel and the forks. Next, re- add the recom- to through the oil to the fork fill fill plug. Repeat the procedure checking test-ride the bike, it for good suspension performance. If a change of fluid does not result in install When you install the the forks, securely block the motorcycle front wheel off the ground, and then follow the specific up with the procedure in the shop service manual for the motorcycle you are working on. The following procedures are typical. Disconnect the speedometer cable (Figure 24-20; see Figure 24-4 for details.) pers Then disconnect the brake cali- and remove the front wheel. Place a wooden wedge keep the brake or other object into the caliper assemblies to pads from falling out (more on this in Unit 25). the front fender. Remove install in- fork springs, the greater pitch (the (Figure 24-23). assemblies into the bridge and steering Install the fork assemblies. Be sure to torque all clamp bolts to specifi- wheel and brake assemblies, as well as any accessories (e.g., the fender and the speedometer ca- mended type and amount of move Then space between the spring coils) should be at the bottom ble) parts. install the seal structions. re- and replace any worn is washer. Assemble the inside components in the order you To for wear, and disassembled them. Be sure to follow the shop manual in- them seal, it and tighten the Allen bolt and performance, you will need to disassemble the forks, spect free length with tube inside the outer tube. and cations. Install the good suspension its shorter than specifications, the snap ring. the dust cover at the is spacer and seal by driving them in with a seal driver. InInstall the inner drain out of the fork. it worn out and should be replaced. Apply hydraulic oil to the fork stall out of the fork, apply the front brake while you push up and place the drain plug oil to by measuring the coil spring a measuring tape. If that torcycle you removed. from its Fill blocks and the oil forks with the recom- and then remove the mo- test the suspension action. Rear Suspension Servicing Wear the in the rear suspension occurs chiefly swing arm pivot bushings, the shock absorbers. Wear in the bearings causes poor swing coil at three points: spring, and the swing arm pivot bushings or arm action. Wear in the coil spring results in too soft a ride and the possibility of rear wheel hop. Finally, if the shock absorbers wear out. they 380 UNIT 24: Frame and Suspension SPRING RETAINER SPRING SPRING ADJUSTER (ASSEMBLED) Figure 24-17. The shock absorbers are located inside the coil springs. (Yamaha Motor Corp. U.S.A.) CHAIN SLACK will fail to that dampen To check NORMAL AXLE POSITION and support the rear of the motorcycle. from side U.S.A.) to side. to unbolt Remove wheel assembly, and grab the swing arm and First, lift the rear try to move There should be no noticeable side the swing arm up and down. The arm move smoothly, without tightness, binding, or rough spots that might indicate damaged bushings or bearplay. Figure 24-18. Wheel travel is limited by a drive chain. (Kawasaki Motors Corp. you will have from the bottom of the arm. the rear swing arm, the shock absorbers it final the springs properly, resulting in a bike bounces excessively. Then move should ings. SUSPENSION 381 UNSCREW TO REMOVE CABLE FRONT BRAKE HOSE CLUTCH HOSE \ FILL PLUG CAP BOLT FUSE BOX SPRING CLIP -/-^ SPRING SPEEDOMETER CABLE Figure 24-20. Disconnect thie speedometer cable. (Honda Motor Co., Ltd.) DAMPER ALLEN BOLT J Figure 24-19. Location of the drain and fill plugs on a front fork. (Yamaha Motor Corp. U.S.A.) If 24). you find a or bearings. and problem, remove the pivot bolt (Figure 24- and then remove the swing arm. Replace Then reinstall the In order to moved from lubricate the bushings or bearings Figure 24-21. coil spring, under tension. will it have to be not remove Using the recommended tool, it from the Wear eye pro- compress the coil spring (Figure 24—25) until the spring retainers can be re- moved. Use measuring tape to measure the free length of the coil spring. If it is shorter than specifications, replace the is extremely The shock absorber can be checked leakage or a bent tube or rod. difficult to test a if the rear wheel has been remove remainLtd.) visually for signs of On the other hand, it it shock absorber for good by hand. The best rule is that bouncing or hopping, replace the shock absorbers. coil spring same compressing CAUTION: Wear tool rear eye protection.) wheel assembly and operation. on the shock absorber, using the you used coil-spring assembly back spring. fluid fork to Motor Co.. damping action by working Replace the a Pump ing fluid. (IHonda re- (SAFETY CAUTION: The Do shock absorber without a compressing tool. tection.) all swing arm. check the the shock absorber. coil spring is new bushings to remove Mount on the bike. Finally, test the rear it. (SAFETY the shock-andreinstall the suspension for proper 382 UNIT 24: Frame and Suspension OUTER BUSHING 1. 2. OILSEALRING OILSEAL CENTER Figure 24-22. Remove set ring or (Kawasaki Motors Corp. U.S.A.) BUSHING circlip. BOLT <*«. Figure 24-24. Rear swing arm disassembly and assembly. (Honda Motor Co., Ltd.) SMALLER PITCH LARGER PITCH Figure 24-23. Install coil springs with wide pitch toward the bottom. (Yamaha Motor Corp. U.S.A.) Figure 24-25. Using a spring compressor remove a spring from a shock absorber. (Honda Motor Co., Ltd.) to NAME DATE SECTION . Job Sheet 24-1 CHANGE FRONT FORK HYDRAULIC OIL Before you begin: Read pp. Make of Motorcycle Time Model Time Finished Started Flat-rate Total Year . Time Time Special Tools, Equipment, Parts, and Materials Drain pan Replacement oil Eye protection Measuring container Funnel References Manufacturer's Shop Manual Specifications Look up the type Oil type and amount of Oil oil for each front fork, and write them in the spaces below: amount Instructor check Procedure 1. Remove 2. Place a drain pan under the fork and remove the drain plug. 3. Apply the 4. Install the drain plug. the filler caps at the top of the fork. front brake and pump the forks to remove any additional oil in the fork. 383 5. Repeat steps 1^ at the other fork. Instructor check 6. Measure out the correct amount of 7. Using a funnel, pour the correct amount of 8. Replace the 9. Repeat steps 6-8 for the other fork. filler oil for the fork. oil in the fork. cap. ^ 10. Check the forks for good suspension Instructor check action. NOTES Instructor 384 check Date completed NAME DATE SECTION Job Sheet lis DISASSEMBLE, INSPECT, AND REASSEMBLE A FRONT FORK Before you begin: Read pp. Make of Motorcycle Time Started Flat-rate Model Time Finished Total Year . Time Time Special Tools, Equipment, Parts, and Materials Measuring tape Fork overhaul parts Seal driver Eye protection ' Drain pan Funnel Replacement oil References Manufacturer's Shop Manual Specifications Look up the specification for coil spring free length and write it in the space below: Coil spring free length Instructor check Procedure 1. Block the motorcycle up safely, with the front wheel off the ground. 2. Remove the front wheel. 3. Remove the speedometer cable. 4. Disconnect the front brake calipers and remove the front wheel. 5. Remove the front fender. 385 386 6. UNIT Frame and Suspension 24: Loosen the bridge clamp bolts and remove the forks from the motorcycle. Instructor check from the forks. 7. Drain the 8. Remove 9. Pull the inner tube out of the outer tube. 10. Remove 11. Clean oil the Allen bolt from the bottom of the fork assembly. the fork seal snap ring and seal. parts in cleaning solvent. all Instructor check 12. Examine 13. Measure the all parts for wear or damage. free length of the coil spring Too Acceptable and compare your measurements with specifications. Is the spring: short Instructor check 14. Lubricate a all new the components with hydraulic seal with a seal driver, 15. Install 16. Install the parts in the fork assembly oil. and replace the snap ring. in the correct order. Instructor check assembled forks on the motorcycle. 17. Install the 18. Fill the 19. Install all the accessories 20. Remove forks with the correct the bike amount of recommended oil. you removed during disassembly. from the blocks and check the front forks for correct suspension action. NOTES Instructor check Date completed NAME SECTION Job Sheet DATE 8. If the bushings or bearings are worn, remove the pivot shaft nut and withdraw the pivot shaft. punch may be needed 9. 10. arm from Separate the swing Drive or press out all A hammer to drive the pivot shaft out. the frame. bushings, bearings, seals, and spacers from the swing arm. Instructor check arm 11. Inspect the bushings or bearings, pivot shaft, and swing 12. Reassemble the swing arm, replacing old components with new ones as necessary. 13. Test the swing Instructor 388 check arm for for wear. smooth operation. Date completed and a drift NAME DATE SECTION Job Sheet . 24^ CHECK REAR COIL SPRINGS AND SHOCK ABSORBERS Before you begin: Read pp. Make of Motorcycle Time Time Finished Started Flat-rate Model Total Year . Time Time Special Tools, Equipment, Parts, and Materials Coil spring compressor Eye protection Measuring tape References Manufacturer's Shop Manual Specifications Look up the specification for rear coil spring free length and write it in the space below: Coil spring free length Instructor check Procedure 1. Remove 2. Using a the coil-spring-and-shock-absorber assembly by coil bolts. spring compressor, compress the shock absorber spring until the spring retainers can be removed. (SAFETY CAUTION: Wear 3. removing the upper and lower retaining eye protection when doing this job.) Release the spring tension and remove the spring and other parts from the shock. Instructor check 389 4. Inspect the hydraulic shock absorber for oil leakage and obvious damage. 5. Check 6. Measure the the shock's resistance to compression Correct free length of the coil spring Too and extension by moving the shock and compare it with specifications. in and out by hand. Is the length: short Instructor check 7. Using the compressor, reassemble the coil spring onto the shock absorber and lock the assembly retainers. 8. in place with spring _. Reinstall the coil-and-shock-absorber assembly on the motorcycle. NOTES Instructor check 390 Date completed CHECKUP KEY TERMS 391 Telescoping forks: motorcycle front suspension consisting of a set of inner and outer tubes that are controlled by a Coil spring free length: the length of a coil spring when it is not compressed; used to determine whether the spring is worn. and hydraulic damping. Tubular frame: a common type of frame constructed from tubes welded together for a strong, light structure. Shock absorber: a hydraulic device connected at coil spring one end and to the wheel at the to the frame other end; used to CHECKUP control spring oscillations. Stamped- steel frame: type of frame used on small motorcycles and mopeds; welded from pressed Suspension: system of linkages, dampers used to Identify the parts of the frame steel. springs, and hydraulic suspend the front and rear wheel of the the spaces provided. 1. motorcycle. 2. Swing arm: motorcycle rear suspension system pivoting rear fork that is that uses a attached to the rear wheel and controlled by a coil spring and shock absorber. 3. 4. by writing their names in UNIT 392 24: Frame and Suspension Identify the parts of the steering their names in the head assembly by writing spaces provided. 5. 6. 7. 9. 10. 11. 12. Identify the names frame and steering dimensions by writing their in the spaces provided. 13. 14. 15. 16. 17. 18. STEERING AXIS LINE VERTICAL AXLE LINE TRAIL CHECKUP Identify the parts of the front fork by writing their names in the spaces provided. 19. 20. 21. 22. 23. 24. 25. a |S3| 393 UNIT 394 24: Frame and Suspension Identify the parts of the rear names in the swing arm by writing their spaces provided. 26. 27. 28. 29. 30. DISCUSSION TOPICS AND ACTIVITIES 1 Change the rear coil spring settings on a motorcycle do the riding characteristics change as the coils How get stiffer? 2. Measure the suspension travel a dirt bike. Which has the on a road bike and on most travel? Why? I he down purpose of the motorcycle brake system is to slow the rotation of the wheels to allow the rider to slow or stop the bike. The system has a lever which is squeezed by the hand or pushed by the foot, producing a force that wheel brakes, which develop is transferred to the to slow the motorcycle. There are two basic types of brake systems lic friction mechanical drum brake and the hydrau- in use; the disc brake. In this unit, we describe the operation and servicing of both types of brakes. JOB COMPETENCY OBJECTIVES When you be able finish reading and studying this unit, you should to: BRAKE SYSTEM OPERATION AND SERVICING Describe the parts and operation of mechanical drum 1 brakes. Describe the parts and operation of hydraulic disc 2. brakes. Adjust mechanical 3. drum the lever brakes. drum needed by several inches, so a cable is used to provide flexibility. 4. Service a mechanical 5. Service a master cylinder. (Figure 25-3) connected to a rod which 6. Service a disc brake caliper. nected to the rear wheel brake mechanism. brake. The used rear brake at the rear is often operated by a foot-pedal lever in turn is A brake because the distance between the brake lever and the rear brake does not change MECHANICAL DRUM BRAKES con- rod can be much as the wheel goes up and down. The foot-operated brake pedal same kind of leverage lever provides the Mechanical drum brakes are the oldest type of brakes used to increase the mechanical advantage. on motorcycles. This brake system uses the mechanical advantage gained by a hand lever or foot pedal to push a set Wheel brake mechanism of brake shoes into contact with a rotating brake drum. Mechanical drum brakes are commonly used on small motorcycles and street dirt bikes. The rod or cable is attached to another lever located on wheel brake mechanism. This lever again multiplies rider's effort to give additional Brake lever lever is with the hand- or foot-operated brake starts lever, which abling him or her to exert the necessary force on the brake The lever is designed so that with a small effort at itself. acts to multiply the strength of the rider, en- can exert a the lever, the rider much larger force at the hand-operated brake lever is shown in Figure 25-1. The long lever swings on a pivot to pull on a brake actuating cable. With a 1-inch distance from the pivot to the cable junction, and a 5-inch distance from the pivot to the center of hand pressure, the lever provides a mechancial advantage of 5 to 1. Thus, if the rider squeezes the lever with a force equal to 10 pounds, there will be a force of 50 pounds applied to the brake cable. The The backing front brake is mounted on scoping forks (Figure 25-2) and the bottom of the teleis operated by a cable connected to a hand lever on the handlebar. Normal suspension travel varies the distance between the brake and is mounted stationary is it A return spring plate and is is The lever at components is on which mounted. turned, its position after the released. on the backing plate when are attached from the lever to the backing used to return the lever to is connected vice on the other side (Figure 25-5). tric that, the wheel and an- (does not turn with the plate provides the platform the rest of the nonrotating brake pedal or hand lever brake. A chored so that wheel). the mechanical advantage. The attached to a part called the brake backing plate (Figure 25-4), which Brake action the is The cam to a is cam de- an eccen- used to push brake shoes out and into contact with a rotating brake drum. The brake shoes have a friction lining which contacts the surface of the rotating brake An drum. exploded view of a wheel brake mechanism is shown in Figure 25-6. The mechanism is essentially the same whether it is used on the front or rear wheel. The brake drum is attached to the rotating wheel: the friction between the brake shoes and drum slows and stops the wheel. The backing plate, upon which all the other compo- 395 UNIT 396 25: Brake System Operation and Servicing Figure 25-1. The brake lever provides a mechanical advantage. (Top: Honda Motor Co., Ltd. Bottom: Kawasaki Motors Corp. U.S.A.) nents except the tating cam drum are mounted, by being firmly anchored lever, which receives lever, actuates the the is prevented from ro- to the frame. movement from cam, which then rotates is A the brake and forces the brake shoes outward; the shoes contact the end. drum at one pivot point supports one end of the brake shoes and not acted upon by the cam. the shoes released. away from the A set of return springs pulls drum when Single leading shoe brakes The brake the brake lever is There are two basic types of wheel brake mechanisms: single leading shoe brakes and double leading shoe brakes. They differ in the tional force of the way they are designed to use the rotadrum to help apply the brakes. Use of this rotational force is called the self-energization or self- actuation principle. How the self-energization principle works is shown in MECHANICAL DRUM BRAKES BRAKE LINE BRAKE CALIPER TELESCOPING FORK Figure 25-2. Front wheel and brake assembly. (Honda Motor Co.. Ltd.) LEVER BACKING PLATE RETURN SPRING T^j ANCHOR Figure 25-3. Rear Co., Ltd.) brake. (Honda Motor Figure 25-4. Backing plate and lever assembly. (Kawasaki Motors Corp. U.S.A.) 397 UNIT 398 25: Brake System Operation and Servicing CAM CAM DRUM LINING DRUM FRONT WEDGING ACTION LINING NING PIVOT Figure 25-7. Drum rotation helps force the leading shoe into the brake drum. (Kawasaki Motors Corp. U.S.A.) BACKING PLATE The other shoe is called the trailing shoe. It moves drum rotation, provides no self-energization, and Figure 25-5. Lever-operated cam pushes brake shoes out against the rotating brake drum. (Kawasaki Motors Corp. U.S.A.) against does not do as Since SHOE much SPRINGS to stop the bike. has one leading shoe and one trailing shoe, this type of wheel brake RETURN PIVOTS it shoe mechanism. mechanism is called a single leading Although only one shoe is self-enerwere stopped on a hill and began the motorcycle gized, if rolling backwards, the ing shoe (because the trailing drum shoe would become a lead- rotation reason, the single leading shoe is reversed). For this mechanism is often used on dirt bikes. Double leading shoe brakes The double leading shoe brake is designed to use the selfenergizing principle on both brake shoes. The components BACKING PLATE CAM ACTUATION LEVER CAM of this type of brake are similar to those of the single leading shoe brake, but with an important difference: Figure 25-6. Exploded view of a wheel brake mechanism. (Kawasaki Motors Corp. is U.S.A.) Figure 25-7. The drum rotates is toward the front of the mogoing forward. When the cam turns, the brake shoes are forced against the drum. With a pivot at the bottom and a single cam at the top, one of the shoes is pushed in the direction the drum is turning. This shoe, called the leading shoe, utilizes the push it gets from the cam to move out against the drum, around which it tries wedge to rotate. The drum rotation, the shoe tight against the however, acts drum and viding a good deal of added braking action. to the pivot, pro- on the actuating lever connected to a second actuating lever and cam. The con- necting linkage and the second torcycle as long as the bike cam double leading shoe brake, the brake cam shown are in Figure 25-8. Each brake shoe has its own Each shoe in the double leading shoe mechanism brake cam, and each shoe is by the brake drum, as shown braking force is a leading shoe. forced out in the direction of is in Figure drum rotation 25-9, and the net greatly increased. The double leading shoe brake provides greater stopping power because both shoes have self-energization. The system is about one-and-a-half times as powerful as a single leading shoe system of the same size and is used where HYDRAULIC DISC BRAKES 399 CAM ACTUATING LEVERS DRUM SHOES Figure 25-8. Exploded view of a double leading shoe brake, (Kawasaki Motors Corp. U.SA.) CAM CONTAINER I PIVOT ^^^0^ DRUM Figure 25-10. Since liquids are not compressible, the piston cannot move, (Kawasaki Motors Corp. U.S.A.) signed to provide the stopping performance required for LINING PIVOT these bikes. Principles of hydraulics CAM Figure 25-9. Operation of thie double leading shoe brake. (Kawasaki Motors Corp. The hydraulic disc brake system uses U.S.A.) draulics to multiply the rider's force in applying the brakes and increased braking this front fer power is required, usually on the wheel of a road machine. The forward weight trans- during braking places most of the braking load on the front wheel. to transfer motion from the hand lever wheel to the brake mechanism. The principles of hydraulic operation of these brakes are relatively simple, but quite important. draulics e.g., is the science of liquids. water or brake tant practical HYDRAULIC DISC BRAKES the principles of hy- fluid, The fact that no Hy- liquid, can be compressed has impor- consequences. Consider, for example, a cyl- inder filled with a liquid and sealed with a piston at one end, allowing no leakage. (See Figure 25-10.) With no While mechanical drum brakes work well enough for lighter, slower bikes, large, stopping power. fast The hydraulic road bikes require more disc brake system was de- outlets for the liquid to escape, the piston will be unable to move, because press the liquid. in order to move it would have to com- UNIT 400 25: Brake System Operation and Servicing INCH 1 MOVEMENT SO. IN. 1 OUTPUT INPUT PISTON PISTON Figure 25-11. Movement of one piston causes movement of thie otfier. (Kawasaki Motors Corp. U.S.A.) If we put an opening at the other end of the container Master cylinder and place a piston there as well (Figure 25-11), force can be transferred between the pistons. For example, a 1-inch movement movement tion travels at the first (input) at the would give a 1-inch piston second (output) piston. This from one part of the brake system Suppose, now, that the area of the 25-1 is 1 1 in- 50 is it to another. piston in Figure first and the force pushing how mo- is Then lb. the The brake on lever master cylinder provides for the system, and the master cylinder means lines to the disc every square inch of surface inside that system has 50 lb of pressure pushing on it. the second piston will be 50 lb/in- of the outlet If the area piston at the other end of the cylinder x 1 1 in^ = 50 lb. This sce- nario illustrates a second important principle of hydraulics: pressure in any part of the system is transmitted equally throughout the system. We can use this principle to force in the brake system. In Figure 25-12, same cylinder measures 2 we have the same 50 An lb/in- of pressure is applied a reservoir of hydraulic fluid means of hydraulic transferred by is brake mechanisms on the wheels (Figure exploded view of a master cylinder ure 25-14. When and a dust boot The The fluid reservoir lb. Remember upon it. We that x2 each square inch has 50 lb or 100 port which of pressure rest. As wear on in', use the same idea in the brake system to in- crease the rider's force. in Fig- exerts keep out is which is in which front of the piston is is connected to the cylinder by two small holes or ports (Figure 25-15). of the piston. The other, smaller port Therefore, the it. lb/in- to piston assembly rides in a cylinder above the fluid reservoir. output piston has 50 lb of pressure upon 50 it dust and prevent leakage of fluid. largest of these is a supply port is shown This piston assembly consists of a piston, two major seals by the input piston, each of the two square inches of the net force on the output piston is the rider pulls the brake lever, force against the back of a piston assembly in the cylinder. the as before, but with an output piston that in-. If ( 1 ) (2) the input force (with a piston as- called cups, a return spring, provide a multiplication of con- 25-13). force on in-, the is is sembly) for the hydraulic system. The force developed by pressure in the cylinder will be 50 lb/in', or 50 psi. This that system a disc hydraulic brake nected to a hydraulic device called a master cylinder. The The towards the back is when a pressure relief the piston the brake pads increases, the is at amount of brake fluid must be increased to maintain proper hydraulic pressure. The reservoir tank supplies this brake fluid. prevent air from entering the brake line fluid level lowers, especially on a rough road or clined position, a compensating which rises when and lowers with the To the brake in an in- diaphragm (Figure 25-14) fluid level is provided for the reservoir tank. When the rider pulls the brake lever, the piston forward easily until the first seal, passes the pressure relief port. At this point, there where is no- for the fluid in front of the piston to escape to, and the pressure begins to build up in the system. The pressure exerted evenly along the inside of the whole system Figure 25-12. How force is multiplied in a hydraulic system. (Kawasaki Motors Corp. (Figure 25-16) and U.S.A.) to the disc is moves called the primary cup, is transmitted through a hydraulic line brake mechanism at the wheel (Figure 25-17). HYDRAULIC DISC BRAKES BRAKE CALIPER ® Figure 25-13. Master cylinder. (Honda Motor Co, Ltd.) 401 402 UNIT 25: Brake System Operation and Servicing PRESSURE RELIEF PORT SUPPLY PORT / •PISTON (AT REST) RUBBER DIAPHRAGM CYLINDER PRIMARY CUP Figure 25-15. Passages to the cylinder from the reservoir. (Yamaha Motor Corp. RESERVOIR U.S.A.) CYLINDER DUST BOOT Figure 25-16. When traps fluid tor Corp. U.S.A.) v^/ard, SNAP It PISTON CLIP RETAINER CLIP Figure 25-14. Exploded view of a master cylinder. (Yamaha Motor Corp. U.S.A.) MASTER CYLINDER Figure 25-17. The pressure buildup from is transmitted through lines to the disc brakes. (Yamaha Motor the master cylinder DISC BRAKE Corp. U.S.A.) moves for(Yamaha Mo- the piston in front of it. HYDRAULIC DISC BRAKES PAD CYLINDER 403 PAD "A" DISC DISC (STATIONARY! 25-18. Cross-sectional view of a simplified caliper. (Kawasaki Motors Corp^ Figure Figure 25-19. Operation of tfie caliper dur(Kawasaki Motors Corp. U.S.A.) ing braking. U.S.A.) assembly Caliper CALIPER CYLINDER As Figure 25-18 shows, the fluid pressure from the master cyhnder is transferred by means of a hydraulic line to another hydraulic component called the brake caliper. The pressure forces the brake pads against the brake disc to slow and stop the rotation of the wheel. A in simplified cross-sectional Figure 25-19. A ton. seal this piston. ride rial, The caliper view of a caliper body has a cylinder The on each side of the rotating is caliper it shown which is held in the caliper body fits around The two brake pads, each with frictional mate- tached to the wheel and rotates with hold is for a pis- assembly is which disc, is at- it. mounted on two shafts which onto the front fork or rear suspension. The caliper thus free to move sideways on the shafts to keep the disc centered between the pads. When ton is pressure builds up in the caliper cylinder, the pis- pushed towards the disc. Between the piston and the pad (A). As the piston moves toward the disc, it pushes the pad ahead of it. When the pad touches the disc, which has no side-to-side play, the pad and piston disc is the brake The can go no further. caliper assembly then slides in the movement. As the caliper slides over, another pad (B), which is firmly mounted in the caliper half opposite the piston, moves into contact with the disc as shown in Figure 25-19. As more pressure direction opposite to that of piston is applied, the disc wheel stops. The is total distance the caliper moves is is but a almost in- There are no return springs tion designed to brake lever movement stantaneous. is Figure 25-20. Tfie piston seal acts like a re(Yamaha Motor Corp. U.S.A.) turn spring, squeezed between the pads and the fraction of a millimeter, so the braking action seal THE FRICTION BETWEEN PISTON SEAL AND PISTON AND ELASTICITY OF THE SEAL CAUSE THE PISTON TO RETURN TO ITS POSITION. move by making use of in the caliper. the piston back to its torsional its The piston return posi- movement after the is is released (Figure produced by the of the piston seal. The 25-20). frictional force The and torsional elasticity piston seal also serves as an auto- matic adjuster of the clearance between the disc and the pad. UNIT 404 25: Brake System Operation and Servicing Disc BRAKE SERVICING The brake disc (sometimes called the rotor) is attached to the lub of the wheel assembly. The disc provides the brake A The surface for the friction pads. A the disc. ploded view caliper caliper-and-disc mounting is is mounted over shown in ex- to notice, for ex- moved be that the bike uses a lot slow down. In the second case, noise in the fluid you may may have a great deal further than usual to get the motorcycle to stop. to Brake case, first ample, that the brake lever you may get the feeling Figure 25-21. in brake problem usually shows up as either difficulty in stopping or noise. In the wheel brake mechanism. If Or more road usually noticed is you have either of these problems, you will have to adjust, inspect, or service the The hydraulic used fluid in the brake system is called brake The performance of the hydraulic disc brake system highly dependent upon proper performance of the brake brake system before long. fluid. is Brake fluid used. must meet fluid is a specially standards. strict Drum brake adjustment formulated liquid that The most important of these are that the fluid must: When Flow freely at • Have a high boiling point (over 400° F, or 200° C) • Not cause metal or rubber brake parts • Lubricate metal and rubber parts • Be low and high temperatures The rear brake is adjusted by first determining the amount of free play at the brake pedal. As you move the pedal up and down (Figure 25-22), you will feel the pedal to deteriorate rated is fluid is assigned a number, such as Always use ing point. is DOT 4, in the fluid's boil- the type of fluid specified by the In hot weather, If there is justing. under heavy usage, some brake compo500 to 650° F (260 to 345° C), itself rarely gets this hot. Even at these high temperatures, the correct type of brake fluid will not the brake is applied, because of the tremendous As soon pressure inside the system. leased, however, the pressure of temperature can be will turn to gas Any water ize rities it fluid if — that tightly sealed be as the brake oil. re- with a low boiling point exposed to these high temperatures. fluid. Brake is, it attracts moisture fluid Because — it For from contamination, (CAUTION Never : It must it is al- hy- must be kept and away from dampness. Brake protected fluid should especially oil, should never be use gasoline, kerosene, motor transmission fluid, or any fluid containing oil to clean and you must turn the end of the brake rod where nects to the backing plate lever. adjust- con- it Turning the nut in a adjust the brakes so that they are tighter (Figure 25-23). Front mechanical drum brake free play is checked and The free play is measured as shown in Figure 25-24. adjusted at the hand brake lever. at the An brake lever pivot point, adjusting nut freeplay is is provided on the end of the cable. excessive, turn the adjuster so that the cable until the amount of it free play is correct. If the tightens Some- times there are additional adjusters on the brake backing plate. in the system. brake system components; these fluids will cause the rubber cups and seals in the master or caliper units to soften, swell, need ad- free play, the rear brakes Brake inspection very important that water and other impu- grease, and other petroleum products. reused. is reduced, and the effects "tored in clean, dry containers. groscopic much allowed to enter the system will vapor- be kept out of the brake ways be also is A is and not work properly that is immediately this reason, felt. too adjust the rear brake, ing nut provided at the nents reach temperatures of although the fluid To direction that shortens the rod will decrease free play and motorcycle manufacturer. when and then meet resistance as the rear shoes The amount of easy movement is the Use a tape measure to measure this free play, and then compare it with specifications. by the Department of Transporta- which the higher the number, the higher boil easily contact the drum. free play. fluid The move first system tion. takes rod has to be shortened to compensate for lining wear. able to absorb moisture that enters the hydraulic Brake it apply the brakes. Periodically, the brake cable or brake to • on a mechanical drum brake more hand or foot lever movement the brake shoe linings system wear, distort, resulting in brake failure.) after adjusting the brakes, the If, if the problem is problem is not solved, or noise from the brakes, you should inspect the brakes. Mechanical drum brakes are inspected by disassembling the drum from the backing same on both the cally the have to safely plate. The procedure front and the rear. is You basiwill block the bike front or rear wheel off the ground. Since the wheel must be removed, you must re- move the brake cable or rod attachment. On a front wheel, you will also have to remove the speedometer cable. To remove the axle and spacers on a rear wheel, you will have Figure 25-21. The disc rotates with the wheel. is attached to and (Yamaha Motor Corp U.S.A.) 405 406 UNIT 25: Brake System Operation and Servicing 10-20mm (3/8-3/4 Figure 25-24. Checking free play. (Honda in) Motor Co.. Ltd.) FREEPLAY LINING THICKNESS Figure 25-22. Rear brake^ (Honda Motor Co.. Ltd.) 25-25. Measuring Figure (Honda Motor Co can have asbestos. ADJUSTING NUT hose: asbestos Figure 25-23. Rear brake adjustment. Do remove chain and axle nuts, and then the wheel. When you as described later. to breathe.) the system will require servic- If not, the backing plate assembly from the drum. Look the brake shoes over carefully; the friction lining material or bonded to the metal brake shoe. of the lining and compare it with specifications manual (Figure 25-25). Generally, than the metal support behind it, is riveted Measure the thickness if in the the lining is shop thinner the brake shoes should be The disc is easy to see. Just look check is it is to run a score that is deep enough signs that parts lining material may can be overheated. Grease or cause {SAFETY CAUTION: Brake noise dust and from poor dirt on the stopping. the brake linings best to catch way to If there your fingernail, then The condition of the disc brake pads can be determined Look inside the caliper where the brake pads are located. Each brake pad consists of a steel backing to visually. which a broken return springs and for over carefully The the disc will require replacement or machining. thickness of the friction pad for it your fingernail across the surface. While the drum is off, check for any obvious signs of wear or broken parts. The brake drum surface should be Look you can reassemble the on the bike. (Figure 25-26) for any signs of scoring. replaced. clean and smooth. it Disc brakes can usually be inspected without disassembly. have the wheel removed, you can separate lining. not blow brake parts off with an air dangerous brake mechanism and reinstall to disconnect the final drive brake Ltd.) show wear, brakes If the ing, is . friction pad is attached (Figure 25-27). is worn down When to the the same thickness as the steel backing, the pads should be replaced. As ward the brake pads wear, the caliper piston to a new position. The different part of the piston gets larger piston seal then moves out- works on a and the area behind the piston and holds more brake fluid. You will notice that BRAKE SERVICING 407 FRONT FORK CALIPER Figure 25-28. Measuring (Honda Motor drum. brake Co.. Ltd.) INSPECT DISC SURFACE Figure 25-26. The disc can be checked visually for scoring. (U.S. Suzuki Motor CIRCLIP Corp.) 0.7 mm (0.028 Remove Figure 25-29. in circlip or snap ring. the master cylinder (Kawasaki Motors Corp. U.S.A.) CALIPER HOLDER place the springs each time you replace the brake lining. r*TJ Use a vernier caliper or a large telescoping gauge to measure the brake drum to determine whether size, or out BRAKE DISC it is oversize drum is worn, over- of round beyond specifications, it will or out of round (Figure 25-28). If the have to be replaced. Small scratches or glazed areas can be re- moved with sandpaper. Reassemble the new shoes and hardware on the backing plate. Install the Figure 25-27. Checking disc brake pads. (Honda Motor Co.. Ltd.) the master cylinder reservoir gets wear. Add more brake fluid, as ment drum brake wheel and brake drum as explained move the cam return springs Remove levers A earlier. Remove Then re- and the connecting rod. Remove the and shoes by folding the shoes inward. the brake cams and check them for thickness and for whether they are bent or warped. Check the return springs for signs of overheating. drum, and the Make an adjust- to the free play as described previously. Hydraulic disc brake servicing: Master cylinder servicing involves the replacement of the brake shoes and return springs. the in the lower as the brake pads needed. Mechanical drum brake servicing Front or rear mechanical brake backing plate wheel assembly back on the motorcycle. It is a good idea to re- problem in a hydraulic disc brake system may be due to the hydraulic system itself or to the mechanical parts of the pads and disc. A hydraulic problem can occur at either the master cyl- inder, the hydraulic line, or the piston per. A and seal in the cali- pressure leak at any of these spots will result in a spongy feeling the lever will action at all. at the brake lever: if the leak is a bad one, have no resistance and there will be no brake UNIT 408 you If first is Brake System Operation and Servicing 25: of these problems with your brakes, find either check the resevoir gone or the master cyhnder. PISTON CUP If the fluid dropped rapidly, the system has a level has (Rember, the leak. in the level does go down slowly as the brake pads wear, but the reservoir should never be empty.) Check over the hydraulic lines and connections. all inside the master cylinder dust boot; any fluid here Look that the cylinder is definitely leaking. caliper is The most leaking. Figure 25-31.- Check the piston surfaces for scratches. (Kawasaki Motors Corp. U.S.A.) inside the cali- per around the piston seal; any fluid outside the seal that the Look means means problem likely is Bleeding the hydraulic system leaky seals in the master cylinder. master cylinder If the and to replace the piston Remove dust boot. a repair kit Remove seals. is available the master cylinder the circlip or snap ring with snap ring Remove the piston and pull out the Remove the clip and remove 25-29). pliers (Figure is at fault, return spring (Figure 25-30). the piston Clean fluid. cup all retainer. Then remove the parts in the liquid in the and brush them with Blow out all passages, orifices, and Then allow the parts to dry thoroughly on a system. Air enters the system draulic parts are disconnected or when A the air. is Connect a vinyl tube oline, eye protection (SAFETY CAUTION: when using shop air. Do not use gas- kerosene, or any other cleaning fluid having the slightest trace of mineral oil, as this will cause damage to rubber parts.) bore If the excessively scratched, the cylinder should too low. re- spill. Use a con- end of the vinyl tube in general, that has any old brake fluid.) Apply the brake lever slowly a few times. With the lever squeezed, loosen the bleed screw. As fluid and air escape, the lever will close. Tighten the bleed screw before the le- ver bottoms on the handlebar grip. is is (NOTE: Do not reuse brake fluid (Figure 25-32). been emitted during bleeding, or hy- to the caliper bleed screw tightly, so that no brake fluid will tainer to catch the brake fluid at the a parts cleaning brush. Wear its the brakes are operated provided on the brake caliper to valve holes. clean paper or a lint-free clean cloth. if trapped air that is when any of the fluid level in the master cylinder bleeding valve move the piston cups. reusable metal parts in alcohol or clean brake Immerse Bleeding hydraulic brakes removes any When bleeding the do not operate the brake lever quickly because the make air, air will be replaced. Brake hoses are available for cleaning cylin- then turn into fine bubbles and der bores, but they must be used carefully to prevent hon- Keep bleeding Dip the new cups in clean brake them on the piston. Then install the retainer and cup, and insert the spring into the bore. Check the piston surfaces and cup surfaces (Figure appear in the vinyl tube. Refill the reservoir with fresh ing the bores oversize. and fluid the bleeding difficult. the air until the air bubbles completely dis- install 25-31) for scratches, and then insert the piston into the cylinder. become stall Avoid forcing the piston — the cylinder wall may scratched, allowing the brake fluid to leak past. In- the snap ring, and install the boot in the master cylin- der groove. tion. Then install the After making sure master cylinder back into posithat the bolts are torqued to specifications, install the hydraulic line. After the cylinder move the air is installed, by bleeding, fill the reservoir and re- as explained below. -^m RETURN SPRING I PISTON ASSEMBLY Figure 25-30. Pull out the return spring. (Kawasaki Motors Corp. U.S.A.) Figure 25-32. Bleed the brakes. (Harley Davidson Motors, Inc.) BRAKE SERVICING rain or high wind. Also, always use fresh fluid from a may closed container; an open container dust. If water is 409 mixed with brake boiling point of the fluid. If collect water or fluid, will it brake fluid is lower the spilled on a painted surface, clean the surface immediately; brake fluid can damage it. Hydraulic disc brake caliper servicing Worn brake disc pads can usually be installed without dis- assembling the brake caliper. Remove assembly. Usually the pads are held LEFT HAND SHOWN (RIGHT SPRING CLIP HAND OPPOSITE) PAD HOLDER move the wheel-and-disc in with clips, so re- Some brake pads have a mark or groove to indicate depth of wear (Figure 25-33). Replace both pads if one or both are worn down the clips to remove the old pads. to the service limit groove. (CAUTION: Use brake fluid or alcohol to clean brake parts, other than the brake pads or the disc. Do not use gasoline or motor rubber parts. Take care that no the brake pads or special solvent to When you oil oil, as they destroy or brake fluid gets on the disc; they should be cleaned with remove any install new pads, it is necessary to push back the piston so that the pads can be easily installed. the piston When pushed back, and the compensating port is open, the brake fluid level Loosen the bleed screw cess brake fluid. if Watch a oily residue.) in the reservoir tank will is rise. necessary, and bleed off the ex- that you do not cause the fluid in the reservoir to overflow. new pads and Install the shoes. A Then is worn out. is pulled out of line. Take care that neither dust nor water contaminates the new brake fluid; don't change the brake fluid outside in a assembly. caliper in its means that must be removed from the The pads are removed, and the bore. The bore and piston must clean brake fluid. If either are scratched or scored, the caliper assembly must be replaced. Pull the old seal out using a sharp piece of tic and install it or plas- bike. scribed. Bleed the system new Then install and mount it on in position. the piston. Finally, reassemble the caliper the wood so that you do not scratch the bore. Lubricate the seal with brake fluid, brake fluid so that the level will again reach the specified The bike to service the seal. piston be cleaned Figure 25-33. Check brake pads for wear depth. (Top: Honda Motor Co., Ltd. Bottom: Harley Davidson Motors. Inc.) cups that hold the hydraulic problem in the caliper usually the seal METAL BACKING install the reinstall the disc-and- wheel as previously de- NAME DATE SECTION Job Sheet I25I1 ADJUST MECHANICAL DRUM BRAKES Before you begin: Read pp. Make of Motorcycle Time Started Flat-rate Year Model Time Finished Total Time Time Special Tools, Equipment, Parts, and IVIaterials Measuring tape Eye protection References Manufacturer's Shop Manual Specifications Look up Hand the brake foot pedal and hand lever free-play specifications and write them in the spaces below: foot pedal free play lever free play Instructor check Procedure 1. Move 2. Use a measuring tape to 3. Use a 4. Adjust the rod to set the free play to specifications. the brake pedal wrench back and forth to feel the free play in it. measure the free play. to turn the rear brake rod adjuster to lengthen or shorten the brake rod. Instructor check 410 . you can feel the free play at the pivot. 5. Squeeze the hand lever back and forth 6. Measure the pivot 7. Adjust the cable nut backwards or forwards to set the free play to specifications. free play with a until measuring tape. Instructor check NOTES Date completed Instructor check 411 NAME SECTION DATE Job Sheet 125^ SERVICE A MECHANICAL DRUM BRAKE . Before you begin: Read pp. Make of Motorcycle Time Started Flat-rate Model Time Finished Total Year . Time Time Special Tools, Equipment, Parts, and Materials Eye protection Measuring tools References Manufacturer's Shop Manual Specifications Look up the specification for Minimum minimum brake lining thickness and write it in the space below: brake lining thickness Instructor check Procedure 1. Raise and support the front or rear of the motorcycle on a stand and blocks. 2. Disconnect the brake cable or rod. 3. Disconnect the speedometer cable, 4. Remove the brake backing plate anchor arm, if there 5. Remove the if there is one. wheel axle and spaces. Disconnect the is one. final drive wheel-and-brake assembly. 6. 412 Separate the backing plate assembly from the brake drum. chain if you are servicing a rear wheel. Remove the cam 7. Remove the 8. Remove the return springs and shoes 9. Remove the brake 10. Check 11. Inspect the brake levers and connecting rod. by folding the shoes inward. cams and check them for thickness and bent or warped conditions. the return springs for evidence of overheating. drum for scoring or distortion. Instructor check 12. Measure the thickness of the brake lining and Measure it to specifications. Is the lining: Worn Acceptable 13. compare the brake drum for out-of-round and oversize. Compare your measurement to specifications. Is the drum: Worn Acceptable Instructor check new ones where 14. Reassemble the brake 15. Reinstall the 16. Adjust the brake cable or rod to obtain proper free play. unit, replacing old parts with required. wheel and brake unit on the motorcycle. Instructor check 17. Check the brakes for proper operation. NOTES Instructor check Date completed 413 NAME DATE SECTION ^^ Job Sheet REPAIR A MASTER CYLINDER Before you begin: Read pp. Make of Motorcycle Time Started Flat-rate Model Time Finished Total Year . Time Time Special Tools, Equipment, Parts, and IVIaterials Master cylinder repair New kit brake fluid Eye protection Drain pan References Manufacturer's Shop Manual Specifications Procedure 1. Disconnect the hydraulic brake line from the master cylinder, making sure to catch the brake fluid in a drain pan. 2. Remove 3. Empty 4. Remove 5. Using suitable snap ring 6. Withdraw the the master cylinder the brake fluid mounting bolts, from the cylinder and remove the cylinder from the motorcycle. into the drain pan. the dust boot. pliers, remove piston, piston cups, the snap ring. and return spring from the cylinder. Instructor check 7. Wash all the parts in clean brake fluid. 414 I 8. Inspect the master cylinder bore for scratches, scores, and pits. Is the bore: Damaged Acceptable Instructor check 9. Using parts from the repair kit, reassemble the master cylinder. Lubricate all rubber pads with brake fluid. Instructor check 10. Remount 11. Fill 12. Bleed the brake system. 13. Check the master cylinder to the motorcycle and connect the hydraulic line. the reservoir with new, clean fluid. the brakes for proper operation. NOTES Instructor check Date completed 415 DATE SECTION NAME Job Sheet 515 SERVICE A DISC BRAKE CALIPER Before you begin: Read pp. Make of Motorcycle Time Started Flat-rate Year Model Time Finished Total Time — Time Special Tools, Equipment, Parts, and Materials Eye protection Drain pan Brake Repair fluid kit References Manufacturer's Shop Manual _ Specifications Procedure 1. Disconnect the brake line from the caliper body and catch the 2. Remove the caliper 3. Remove the caliper assembly from 4. Remove the caliper bolts 5. Remove the brake pads. 6. Remove the piston boot and piston. from its mounting its fluid in a drain pan. bolts. mounting on the fork or frame. and separate the caliper bodies. Instructor check 7. Wash 8. Inspect the caliper bore for signs of scoring, scratching, and pitting. Is the bore: Worn 416 all metal parts (except the pads) Acceptable in clean brake fluid. Inspect the thickness of the pad friction material and compare Worn it to the thickness of the metal backing. Are the pads: Acceptable Instructor check 10. Coat the parts with brake 11. Coat the piston with brake 12. Install the 13. Reinstall the caliper bolts using 14. Reinstall the caliper assembly 15. Reconnect the brake 16. Bleed the system 17. Check and fluid fluid install piston seal in the caliper and push it body. slowly into the cylinder. brake pads into the caliper body halves. new dust seals. Instructor check to on the motorcycle, torquing all the bolts to specifications. line. remove all the air. the brake system for proper operation. NOTES Instructor check Date completed 417 418 UNIT 25: Brake System Operation and Servicing KEY TERMS Bleeding: removing air from a hydraulic brake system. Brake drum: the part of the wheel brake assembly that is attached to the wheel. Brake pads: the shoes or friction linings used on disc brake systems. Brake shoes: the friction lining used on drum brake sys- tems. Caliper: a housing for the hydraulic components of a disc brake system. Disc: the part of the disc brake system that turns or rotates with the wheels. Disc brakes: brakes that use a rotor attached to the wheel, and a caliper with brake pads to stop the wheel. CHECKUP Identify the parts of a writing their names drum wheel brake mechanism by in the spaces provided. 1. 2. 3. 4. 5. 6. 7. Identify the parts of the double leading shoe brake ing their names in the spaces provided. 9. 10. 11. 12. by writ- CHECKUP Identify the parts of a master cylinder names 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. in the spaces provided. by writing their 419 420 UNIT 25: Brake System Operation and Servicing Identify the parts of a caliper by writing their names in the DISCUSSION TOPICS AND ACTIVITIES spaces provided. 1. Do 26. 28. 29. 30. this chapter, check the condition of the brakes on the motorcycle you ride. 25. 27. Following the procedures in 3. they need replacement? Disassemble a shop master cylinder. Inspect the conand then reassemble the cyl- dition of all the' parts, inder. and the wheel assembly are an important part The tires and wheels support the weight of the motorcycle and allow it to move down the road. The I he tires of the motorcycle. and wheel provide directional control. The rear front tire and wheel deliver the engine's power to the road to push the motorcycle forward. In this unit, we describe the tire and servicing of the parts, operation, tires and the wheel JOB COMPETENCY OBJECTIVES When you be able finish reading you should this unit, to: Identify the parts 1. and studying AND WHEEL OPERATION AND TIRE assembly. and explain the operation of a SERVICING tire and a wheel assembly. 2. True a wheel for 3. Replace a broken spoke. 4. Remove and 5. Disassemble, clean, lubricate, and and lateral radial runout. replace a rim. The wheel bear- install ings. tread section of the tire provides the area of traction with the road. The tread cool the tire and is designed to allow Treads are made of a rubber compound that TIRES tant to abrasion. Tires have ion two basic functions. First, they provide a cush- between the road and the motorcycle wheels shocks transmitted by rough roads. Tires bumps flex, to absorb or give, as are encountered to reduce the effect of the shock Second, the the rider. tires on provide frictional contact be- tween the wheels and the road for good traction. Good motorcycle to transmit power through traction enables the the tires to the road for rapid acceleration, to resist the ten- dency of the bike to skid on turns, and to come to a quick stop when While is it is ber, and construction common A of a tire is The main beads. steel structural Each bead which does not touch the road, is is element of a tire its is two wire is specially in the road and not as thick as the TREAD made of rubber, it number of parts made from difshown in cross section in Figure 26-1. highly resis- cord plies from damage. The side wall rub- to think of a tire as really constructed ferent materials. is thick layer of tread rubber designed to help absorb irregularities to protect the Tire parts flow to compounded to withstand road wear and provide traction. The spaces between the treads permit distortion of the tire on the road without rubbing that would accelerate wear. Most street tires have wear bars or tread wear indicators (TWI) between the treads. These are raised sections moulded into the tire tread. An arrow on the tire side wall points to the locations of TWIs. When the tire wears down, the tread wear indicators come flush to the surface, signalling that a new tire should be purchased. The sidewalls are made of a different grade of rubber that is the rider applies the brakes. The air wet weather. to channel out water during INNER LINER formed by wrapping together several wires for a continuous hoop. The basic strength of a structure, called its tire is determined by its internal carcass or casing. The carcass consists of layers of rubberized metal or fabric called plies and belts. Each ply is cords imbedded in a layer of rubber with metal or fabric its a variety of materials, body. The cords may be made from such as rayon, nylon or polyester, fiberglass, steel, or aramid. The type of RIM VALVE CHAFER material used de- termines the tire's stability and resistance to bruises, fatigue, and heat. The plies are wound the beads at their and bonded into the sides of the ends around tire. Figure 26-1. Cross-sectional view (Honda Motor Co., Ltd.) of a tire. 421 UNIT 422 26: Tire and Wheel Operation and Servicing when it is depressed (for lowering The core can be unscrewed out of the valve sure and to escape air pressure). for quick tire deflation. The valve cap keeps the core clean and serves as the final seal. The screwdriver-type of cap has a forked tip which can be used to remove and replace valve cores (Fig- VALVE PIN ure 26-3). Motorcycle sizes TAPER SEAT CORE ter of the rim that the many in Common on. tire fits 18 and 19 inches. ters are 16, 17, used manufactured are tires different and designs. Tire sizes are determined by the diametire rim diame- The diameter of the tire determined by the size and use of the motorcycle. is Tire tread designs have been developed for different RUBBER COVER types of motorcycles and different riding conditions. of lection Knobby tread designs tire shown is in A se- Figure 26-4. treads are used for off-road riding because they provide good traction in the dirt. Rib treads are used on the front (never the rear) of road bikes because they provide good directional control. A number of tread patterns, on the rear of road bikes. called universal treads, are used markings Tire Figure 26-2. Tube valve assembly. Army) Tire manufacturers have adopted a tire marking system that (U.S. provides information about the construction, size, pressure, and speed ratings, as well as other important infor- mation, for motorcycle system is shown tires. in Figure the side of the tire Figure 26-3. A valve can be used Army) to tip cap w^ith a screwdriver remove a core. (U.S. markings, tire maximum made of an is is tells marking tire tire. One of the which the the direction in tire shown with an arrow. The speed referred to a speed chart, tell can be safely ridden. The load index code that tread but is when of a something about the tell most important items should rotate, which An example 26-5. Each of the markings on how much weight is how fast the a numerical a tire can support. abrasion-resistant rubber to provide protection for the structural plies. Inflation pres- Tire pressure sure and the stiffness of the cords account for the rigidity of sidewalls; the sidewall rubber has almost nothing to do with it. In general, the more plies a tire has, the stiffer the Correct tire pressure is necessary for safe driving, good tire mileage, and responsive steering. Tires should be checked make recommended sidewalls, and, therefore, the less cushioning the tire gives frequently to the rider. pressure. Tire pressure should be checked with an accurate The tire is filled rate inner tube to strip is air. Most motorcycles use air inside the tire. them is the bead area Tubes Some motorcycle contained inside the a sepa- rubber rim by air The by tires are tubeless. carcass, sealed tire between the rim and the are inflated into the tube tire. under pressure. Air is forced through the valve, which automatically pre- vents the air from escaping (Figure 26-2). is A used between the wheel rim and the inner tube to protect the tube. air in with hold the threaded inside and out at the end to The accommodate valve stem the valve core and cap. The core escaping. A is a spring-loaded seal that prevents air from pin on the core allows air to enter under pres- sure that they are at the pencil- or dial-type gauge; service station air gauges are frequently inaccurate from rough use and should not be de- pended upon for an accurate pressure reading. To check the pressure, remove the valve cap from the gauge check firmly over the valve. The pencil-style gauge scale extension will then pop out of the gauge (Figure 26-6), at which time you can read tire valve and push the the pressure on the scale. tire The dial-type gauge has a needle that points to the tire pressure. The specifications for correct tire pressure are provided in the motorcycle owner's manual and the shop service manual. Correct inflation (Figure 26-7, right) permits tread contact on the pavement with relatively full even force UNIVERSAL UNIVERSAL UNIVERSAL UNIVERSAL UNIVERSAL UNIVERSAL TREAD TREAD TREAD TREAD TREAD TREAD f^'S RIB TREAD TREAD SPORT TREAD TUBELESS TUBELESS HIGH-SPEED HIGH-SPEED KNOBBY TREAD UNIVERSAL USED ON FRONT OR REAR REAR TIRE DESIGN Figure 26-4. Tire tread designs. (Avon Tyres Ltd.) 423 UNIT 26: Tire and Wheel Operation and Servicing 424 MANUFACTURERS NAME OR BRAND NAME COUNTRY OF MANUFACTURE A COMMERCIAL NAME OR IDENTITY TIRE CONSTRUCTION DETAILS (NOT REQUIRED IN U.K.) REAR TIRE FITMENT LOAD AND PRESSURE MARKINGREQUIREMENT NORTH AMERICAN TIRE IDENTIFICATION NUMBER (NOT APPLICABLE NORTH AMERICAN DEPARTMENT OF TRANSPORT COMPLIANCE SYMBO IN U.K.) TIRE SIZE DESIGNATION SPEED SYMBOL LOAD INDEX ARROW DENOTING ROTATION THE DIRECTION OF WHEEL SPEED SYMBOL THE WORD TUBELESS WHERE APPLICABLE Figure 26-5. Tire markings. (Avon Tyres Ltd.) Uneven wear on pavement slipsi Uneven wear Figure 26-7. Comparison of high, low, and correct air pressure in a tire. (Kawasaki Motors When Corp. U.S.A.) a tire has too little air pressure to properly support the load, the central area of the tread rises upward at the point of road contact, as the sidewalls flex. This motion concentrates tremendous stress on the outside edges of the tread, as Figure 26-6. Checkirng tire flatten, throughout the tire offers full width of the tread. maximum greatly extended tire its full A properly inflated resistance to skidding and provides life. The tread will wear throughout width, and the original shape will be maintained each edge of the tread. shown in Figure 26-7 (center), causing maximum wear on those edges and minimum wear at the center portion of the tread. Moreover, low pressure allows the tire to pressure. at shifts the sidewalls from become more flexible, and the rim side to side over the center of the tread. The rider feels these changes as a slight side-to-side instability: the motorcycle feels Excessive flatten tire mushy when turning comers. pressure does not allow the out at the point of road contact. The tire tread to central portion WHEEL ASSEMBLY Figure 26-8. Dismounting the moving the (Yamaha tube. 425 tire and reMotor Corp. U.S.A.) of the tread then wears heavily (Figure 26-7, DETAIL: High left). CAST WHEEL pressure produces hard riding characteristics and reduces pavement. the ability of the tire to grip the bend up away from the road on the becomes stiffer, but less rubber so the tires can skid more is makes The tire also It the tread side. in contact with the road, heavy braking for easily under cornering. Tire repair One of the most common a tire is punctured, the rim, it tire problems is a flat tire. When Figure 26-9. Motorcycle equipped with cast wheels. (Top: U.S. Suzuki Motor Corp. must be dismounted from one side of Detail: and the tube must be pulled out. The tube can then Honda Motors Co.. Ltd.) be patched or replaced. To remove the tire, first unscrew move the valve core. When all the the valve cup and air is out of the tube, from (both sides of) the rim by with your foot. Use two tire removal re- The tire assembly is reinstalled by reversing the disas- separate the tire bead step- sembly procedure, with one difference: ping on the irons has been installed, but before the tire (with rounded edges) and begin to work the tire bead over edge of the rim, starting 180 degrees opposite the tube the stem (Figure 26-8). Take care to avoid pinching the tube as you work. you can slip the tube out. tire completely Be very careful not damage the stem while pushing it back out of the rim you are changing the tire itself, finish the removal by working the tire off the same rim edge. Once the tire is off the rim, examine its inside for signs to right after the tube has been completely slipped onto the rim, inflate the tube. Inflation any creases that might exist. Then stem is removes release the air and con- tinue with reassembly. Right after the tire has pletely slipped onto the rim, After you have worked one side of the off the rim, tire check to make been com- sure that the squarely in the center of the hole in the rim. WHEEL ASSEMBLY hole. If of damage. jury may A ply separation near a puncture or other in- not be easy to see; probing detect separation. If the damage patch, or boot, the inside of the A puncture the tube in the and holding is is the only not great, way to you can tire. tube can be located by putting air in it under water. The tube can then be patched or replaced, depending upon its condition. The wheel assembly supports the tire and provides for a center mounting on the motorcycle through an axle. There are two types of wheel in use: the spoked wheel and the cast wheel. The cast wheel (Figure 26-9) is becoming the more popular for the larger road bikes. In this type of wheel, the wheel hub center and rim are cast as one piece from an alloy of aluminum or magnesium. This construction requires very makes little for a very strong maintenance. and light wheel that 426 UNIT 26: Tire and Wheel Operation and Servicing Figure 26-10. A motorcycle with a spoke-type wheel. (Top: Kawasaki Motors Corp. U.S.A. Detail: Honda Motor Co., Ltd.) The spoke wheel the oldest type of motorcycle wheel is used on most small and mediumThe wheel (Figure 26-1 1) is made up of components. The outside of the wheel is round rim made of steel or an aluminum al- (Figure 26-10). It is still size motorcycles. RIM basic three formed by a loy. The center of the wheel provides the mounting for the The hub and rim both have The spokes fit hub and go out to the rim, where they axle (to be discussed shortly). holes drilled in them to accept spokes. through holes in the are held in position with threaded nipples that fit through holes in the rim. The spokes are arranged in an overlapping pattern. Once they are installed (called lacing the wheel) and tensioned properly, the resulting wheel is extremely light, yet ex- tremely strong. Most wheels have terns are 36 or 40 spokes. Several pat- either used to lace the wheel according to which wheels are described as cross 1, 2, 3, or 4. patterns at is as follows. Each spoke rationale of the wheel is installed an angle from the hub to the rim. The angular position of the spoke allows it to absorb braking forces. In forming may cross over a of the hub) on SPOKES The in the way to the rim. If spoke only, it crosses over two spokes, Cross 1 power transmission and particular angle, each spoke number of other spokes (on its is its a cross 1 it is it the same side crosses over one pattern (Figure 26-12). If it a cross 2 pattern, and so on. and cross 2 use very short spokes, resulting in a very light wheel. Cross 3 and cross 4 use longer spokes, providing a heavier, more rigid wheel. Figure 26-11. Parts of a spoke (Yamalia Motor Corp. U.S.A.) wheel. steels and Each spoke has a head, blade. Spokes are manufactured from high-quality are usually chrome plated. WHEEL ASSEMBLY 427 CROSSES OVER THIS SPOKE AND NO OTHER) MORE THAN t^ INNER SPOKE LESS 1^ THAN 3 C J lllllllllll THREADED BUTT 90° C 1 OUTER SPOKE Figure 26-12. The spokes cross over one spoke on the same side of the hub in a cross 1 pattern. (Mid American Vocational BLADE 90° l l lllllllll SPOKE LENGTHFigure 26-13. Spoke parts and types. (Mid American Vocational Curriculum Consor- Curriculum Consortium) tium) The wheel and threaded butt (Figure 26-13). The length of the spoke is measured from the head to the end of the threaded with the head fitting through the holes in the hub. area, The trued by is or radial runout to is determining where the first correct the runout. The spokes are tensioned with a spokes used on the inside of the hub are called inner spoke wrench (Figure 26-16), which spokes and have a head angle of more than 90 degrees. nipple. The spokes used on the outside of the hub are of course outer spokes and have a head angle less than 90 degrees. The different head angles are necessary to aim the spoke tension. around the hub and directly at The nipple When you to-side (Figure 26-17) the rim. is obvious whether the rim Truing a wheel right. If it the right; A new wheel with a perfectly round rim and properly ten- lateral runout). If the the to wheel hits an obstacle hard enough, rim can get damaged and spokes can eventually begin loosen up. show When this happens, the wheel may begin to is called The wheel is removed from the bike, and the tire dismounted. The wheel is then installed on a truing stand (Figure 26-15), which supports it in its center hub truing a wheel. and allows you to rotate stand is it. An adjustable pointer on the adjusted near the wheel and is used to visually de- termine the amount of runout (Figure 26-14). Some stands have a dial indicator for very accurate runout measurements. is spin the rim, out of true to the you need left, to pull it will be it or to the left back into out to the right, you need to pull As you look fit it to the at your wheel, notice that half of the spokes hub and the other half fit into hub (Figure 26-18). Find the runout wheel and mark it with chalk or a grease pencil. into the left side of the the right side of the area in the Suppose, for example, pull the rim to the either or both kinds of runout (Figure 26-14). Correcting a wheel for lateral or radial runout out to the it As you is side- runout left. sioned spokes will rotate without either up-and-down variation (called radial runout) or side-to-side variation (called is if on the stand and observe in relation to the pointer, lateral present. is over the spoke fits turned to tighten or loosen the spoke spin the wheel movement lateral located and then tensioning the spokes is it off to the left. Then you can any area by tightening the right in spokes just opposite that area on the left side of the hub. Tighten several of the left-side spokes just slightly and keep checking to see also loosen spokes The trick is to how on the make the rim is responding. right side to get the You can same effect. small corrections, tightening and loos- ening, and end up with spokes that are all tensioned about the same. Correcting radial runout is a lot harder. wheel, look for up-and-down movement As you spin the or hop between UNIT 428 26: Tire and Wheel Operation and Servicing RIM- GAUGE TIRE RADIAL RUNOUT STAND CHECKING TIRE RADIAL RUNOUT TIRE LATERAL RUNOUT POINTER ^^-^ GAUGE Figure 26-15. Wheels are trued truing stand. (Harley CHECKING TIRE LATERAL RUNOUT in a wheel Davidson Motors, Inc.) Figure 26-14. Wheel radial and lateral run(Harley-Davidson Motors, Inc.) out. the pointer and the rim (Figure 26-19). First, try to deter- mine whether the hop If a high spot is which the high spot do so, tighten a is due to a high spot or a low spot. the problem, the side of the wheel is located has to be group of spokes on made lower. on To that side of the wheel, and loosen a group of spokes on the exact opposite side, shown in Figure 26-20. Anytime you correct a rim for one type of runout, you should recheck it to make sure you have not created the as Figure 26-16. Spokes are tensioned with a spoke wrench. (Yannaha Motor Corp. U.S.A.) other type. Keeping the spokes properly tightened during truing is an art. Good wheel with their fingernail and listen how tight or loose a course, takes a spoke is. twang the spokes to the pitch. This tells them This kind of knowledge, of builders good deal of experience. broken spoke head end out of the hub, and unthread the nipple from the blade end. Get a replacement spoke of the correct length and diameter, and then push this spoke through its hole in the hub in the same direction Pull the you removed Replacing a spoke A severe tire impact can cause one or more spokes to bend Damaged spokes will cause a severe runout conTo replace a spoke, you will usually have to re- or break. dition. move the wheel from the motorcycle and dismount the tire. it. Following the pattern of the rest of the spokes, direct the spoke over to its place on the rim. Start the nipple on the threaded end of the spoke, and tighten the nipple until there are as many threads uncovered as you can observe on the other spokes. Finally, install the wheel in a truing stand wheel as previously described. and true the WHEEL ASSEMBLY 429 POINTER LATERAL OR SIDE Figure 26-17. Wheel with side) runout. (Harley lateral (side-to- Davidson Motors, OUTER SPOKE RUNOUT Inc.) RADIAL RUNOUT Figure 26-19. Locating ley Davidson Motors. radial runout. (Har- Inc.) \ INNER SPOKE HIGH OR LONG AREA TIGHTEN LEFTSIDE SPOKES TO MOVE RIM RIGHT TIGHTEN SPOKES TIGHTEN RIGHT SIDE SPOKES TO MOVE RIM LEFT BRAKE DRUM LOOSEN OPPOSITE AREA RIM TIRE Figure 26-18. Correcting lateral (Kawasaki Motors Corp. U.S.A.) runout. Figure 26-20. Correcting radial runout. A high or long area is corrected by tightening long spokes and loosening short spokes. UNIT 430 26: Tire and Wheel Operation and Servicing The spin it spin it tire and wheel are balance in axis of rotation of the is When mark ends up on heavier there and wheel-and-tire assembly and then it, it with a piece of chalk. tire again. If the chalk is to true to stop rotating. it bottom of the the tom, the wheel A you would the wheel as slowly and wait for mark stops, Now and wheel can be balanced on the wheel truing tire Mount stand. is the bot- out of balance. when the weight of the distributed equally around the wheel (the axle). If the tire and wheel are balanced, the wheel will have no tendency to roFigure 26-21. Taping the spokes to prevent mixup. (Mid American Vocational Curriculum Consortium) by tate regardless of itself, its position. If they are not bal- anced, the wheel will always rotate until the heaviest spot is at A Replacing a rim the bottom. motorcycle wheel balanced by putting corrective is wheel balance weights that are commercially available on A severely bent rim cannot be properly trued without ex- cessive tightening of the spokes. Instead, the rim will need to To do be replaced. so, first motorcycle and dismount the stem hole in the remove the wheel from the Then locate the valve rim and, in direct alignment with all form an X, as shown the nipples from all in the spokes, Tape the where they pencil. spokes together with masking tape in parts cross and make it, Figure 26-21. Remove and then carefully work the rim free of the spokes. Make sure your replacement rim has the same number new rim of spoke holes as the old one. Then, place the with the reference mark you made on valve stem hole and carefully at a the hub. Start at the work one taped pair of time through the rim holes, and then screw the nipples on just a few turns. Continue this procedure until all the spokes are inserted starting at the valve and each nipple is started. Then, stem hole, tighten each nipple about one-half turn. Continue to made by work around the rim until all the in the the amateur from solder. When you heavy part of the wheel, put two find the wheel weights of equal mass on the side of the point opposite the top). If the heavy point stays where move them of the weights or moves point fifth spoke on either heavy point (Figure 26-22, increase the mass it is, closer together. If the heavy to the opposite side of the wheel, the weights are too heavy. In that case use lighter weights. back over the hub and spokes, aligning the valve stem hole spokes on the rim opposite the heavy spot wheel. Spoke-type weights can be tire. on the hub with a grease a reference the spokes or cannot find a heavy spot, the wheel is When you balanced. If you use two weights to oppose the heavy part of the wheel, the tomass is spread out, preventing overstress to any one tal You part of the wheel. also get greater accuracy away from the weights toward or by moving Use the the light point. same approach when using rim weights (Figure 26-22, bottom). Computerized wheel balancers are available that spin the wheel and sense any unbalance. The operator can then add corrective weight to balance the assembly. spokes are tightened to the same tension. Put the complete wheel on the truing stand and true WHEEL HUB ASSEMBLY it. Balancing wheels Any shaking or vibration that the rider feels speeds can be caused by a tire at highway and wheel assembly out of balance. Being out of balance is caused by there be- ing different densities in different parts of the tire, in turn rest of causes one part of the tire to that is which be heavier than the The wheel hub assembly is On serves as the support for the head spoke-type wheels, At highway speeds, the wheel assembly develops great centrifugal force. If the assembly is heavier at one point an important part of the wheel. end of the spokes. The rotation hub provides the mounting drum or brake disc. On the rear wheel, the for the brake hub serves as the mount drive. The hub for the rear sprocket of the final also provides for the mounting of the axle and axle bearings. A it. it cross-sectional view of a front 26-23; the brake parts shown described previously. An hub is ter wheel tates in relation to this stationary axle. In is connected to the steering and suspension systems, any condition causing the front wheel to vibrate will ously affect the life of all parts. In addition, the bike will able to ride. seri- of the suspension and steering be unsafe and uncomfort- is in the front forks. rotation as free of friction as possible, installed in the hub. The hub make order to is very similar. ro- the wheel bearings are The bearings allow the axle to turn while supporting the weight of the motorcycle. hub assembly in Figure have been axle that passes through the cen- mounted than at any others, vibrations will result. Because the front of the hub shown in the illustration The rear WHEEL HUB ASSEMBLY EQUAL ANGLES ,TIRE WHEEL WEIGHTS RIM HEAVY SIDE BALANCE WEIGHT Figure 26-22. Balancing a wheel. (Kawasaki Motors Corp. U.S.A.) FRONT AXLE BRAKE CAM BRAKE ROD SPOKE HOLES BRAKE LEVER Figure 26-23. Cross-sectional view (Honda Motor Co., Ltd.) front hub. of a 431 UNIT 432 26: Tire and Wheel Operation and Servicing Most motorcycles use ball bearings (Figures 26-24) to The bearing assembly consists of an outer race and an inner race which supports the balls. The outer race fits into the hub and has a groove or channel in which several precision balls ride. The balls also fit into a groove in the inner race, whose bore supports the axle. A cage supports and spaces the balls apart. The inside race can :^ support the axle. -BALL BORE turn in relation to the outside race because the balls are free to rotate in both races. With proper lubrication, this INNER RACE type of bearing allows excellent low-friction rotation. Both the front and rear bearings are close eventually get contaminated with dirt. xr^_ -OUTER RACE and to the road Accordingly, they must periodically be removed, cleaned, inspected, and lu- Figure 26-24. bricated. To service the wheel bearings, torcycle up so that the wheel safely block the first to be worked on Ball bearing. (Honda Motor Co., Ltd.) mo- off the is ground. Then remove the wheel assembly. Next, remove the axle nut and pull out the axle. Some bearings have a set of seals on each end of the hub to pre- HUB moisture from getting into the bearings. vent dirt and can be removed by prying them out with a pry good idea to use new seals during reassembly.) Drive out the wheel bearings and spacer (Figure 26-25). These seals BEARING bar. (It is a Use a hammer and brass fully drive drift SPACER BEARING SPACER or bushing driver, and care- on the outer race of the bearing to avoid damag- BEARING ing the ball cage. Wash all {NOTE: Some bearand cannot be repacked with lubricant: do type of bearing.) Wipe excess cleaning sol- the parts in clean solvent. ings are sealed not wash this Figure 26-25. Removing axle bearings from (Yamaha Motor Corp. U.S.A.) the hub. vent off of bearings and other parts with shop towels, and allow them to dry. Then inspect the bearing races and balls As you spin the bearing by hand, smooth movement between the parts. Re- for pits or roughness. you should feel a place any bearing that runs rough, is noisy, or has exces- sive play. The a flat axle can be checked for bending in V-blocks or surface (Figure 26-26). Check on the specification for allowable runout on the axle shaft. If you detect any bending, the axle should be replaced. Use the type of wheel bearing grease recommended in the manual and pack the bearings with grease. Then, placing some grease in the palm of your hand, hold the bearing between the thumb and fingertips of your other hand and force grease against the between the balls palm of your hand by pressing the bearings into the grease. Be sure to coat the outside of the cage and balls with grease. Reinstall the bearings with the drift or bushing driver. Figure 26-26. Check axle shaft ness. (Honda Motor Co., Ltd.) for true- being careful to drive only on the outer race. Then replace the seals how and install the axle. It may be necessary to adjust tightly the axle nut bears against the bearings spacer. Check the shop service Finally, install the wheel in the manual and for this procedure. motorcycle. NAME SECTION . ^ob Sheet DATE 7. Clean off the grease pencil mark from the rim, and continue checking and adjusting until runout does not exceed V32 of an inch. Instructor check 8. Adjust the truing and pointer to indicate radial runout. 9. Spin the wheel and make a mark 10. at the point of maximum radial runout. Correct any radial runout by loosening the spokes directly opposite the marked area by one-half turn and tightening the spokes at the marked area by one-half turn. 11. Clean off the grease pencil mark from the rim and continue adjusting 12. Since you have just adjusted the radial runout, recheck and readjust the lateral runout, until runout does not exceed 'A2 of an inch. if necessary. NOTES Instructor 434 check Date completed NAME SECTION . Job Sheet DATE 26-2 REMOVE AND INSTALL A WHEEL RIM Before you begin: Read pp. Make of Motorcycle Time Started Flat-rate Model Time Finished Total Year Time Time Special Tools, Equipment, Parts, and Materials Spoke nipple wrench Grease pencil Masking tape Eye protection References Manufacturer's Shop Manual Specifications Procedure 1. Remove 2. Dismount 3. Make 4. Use masking tape 5. Use 6. Carefully the wheel the tire a reference from the motorcycle. and tube from the wheel. mark on hub in alignment with the rim valve to tape the spokes together in pairs the spoke nipple work the wrench to remove the nipples where they from all stem hole. cross. the spokes. the rim free of the spokes. Instructor check 7. 8. Place the new rim back over Start at the valve the nipples the hub and spokes, aligning the valve stem hole with stem hole and carefully work one taped pair of spokes on a few at the reference mark on a time through the rim holes. the hub. Then screw turns. 435 9. Continue installing spokes 10. Begin 11. Go 12. all at the the until all the Mount 14. Install the in place and each nipple is on a few turns. valve stem hole and tighten each spoke nipple one-half turn with the spoke nipple wrench. way around the rim until True the wheel for radial and 13. spokes are the tire and inflate it all the spokes are tightened to the same tension. Instructor check _ Instructor check _ lateral runout. to specifications. wheel on the motorcycle. NOTES Instructor 436 check Date completed NAME DATE SECTION Job Sheet . 26-3 DISASSEMBLE, CLEAN, LUBRICATE, AND INSTALL AXLE BEARINGS Before you begin: Read pp. Make of Motorcycle Time Model Time Finished Started Flat-rate Total Year Time Time Special Tools, Equipment, Parts, and Materials Wheel bearing grease New seals Eye protection References Manufacturer's Shop Manual Specifications Procedure 1. Remove the wheel 2. Remove the axle nut and pull out the axle. 3. Use a pry bar 4. to from the motorcycle. remove Use a hammer with the wheel bearing seals from each end of the hub. a brass drift or bushing driver to drive the bearings out of the hub. race only, or you could damage 5. Wash 6. Inspect the bearing balls and races for any pits or roughness. Are the bearings: all parts in cleaning solvent Damaged 7. Check the axle Straight {NOTE: Drive on the outer the bearing.) and allow them to dry. Acceptable by rolling it on a flat surface for bending. Is the axle: Bent Instructor check 437 8. Pack the bearings with the recommended type of wheel bearing grease. 9. Install the bearings in the hub with a brass drift or bushing driver. new seals in either 10. Install 11. Install the axle end of the hub. and axle nut. Instructor check 12. Install the wheel on the motorcycle. NOTES Instructor 438 check Date completed CHECKUP KEY TERMS CHECKUP Lacing: the construction of a spoked wheel by installing Identify the parts of the tire the spokes in a crossing pattern. Lateral runout: the side-to-side wheel as it movement of in the a spoked 1. 2. 3. 4. Truing: the correction of spoke tension to lateral remove the ra- runout from a wheel. Wheel balance: the correction of a heavy spot on one side of a wheel by installing corrective weights on the other side. names spins. wheel. and their spaces provided. Radial runout: the up-and-down movement of a spoked wheel as it spins, caused by high and low areas in the dial by writing 439 5. 6. 7. 8. 9. Identify the parts of a spoke spaces provided. 10. 11. 12. 13. by writing their names in the 440 UNIT 26: Tire and Wheel Operation and Servicing Identify the parts of a in the hub assembly by writing spaces provided. their names Identify the parts of a wheel bearing by writing their names in the spaces provided. 14. 25. 15. 26. 16. 27. 17. 28. 18. 29. 19. 30. : 20. 21. 22. 23. 24. DISCUSSION TOPICS AND ACTIVITIES 1. Completely disassemble a spoked wheel. Following a pattern on a complete wheel, lace the wheel. 2. Try to identify the spoked wheels. spoke pattern on several types of INDEX INDEX 443 Built-up crankshaft, 163-165 Bushing, 156 Adaptor, 22 Adjustable-end wrench, 23 Adjustable pliers, 24-25 Air filter, 236-237 Air- fuel mixture, 239 Cable adjustments, 237 Air impact wrench, 24 Caliper assembly, 403 Air intake, 226 Cam Allen head, 22, 47 Allen wrench, 23 Alloyed, 156 Alternator, Carburetor synchronization, 239-241 301-303 American Petroleum Institute (API), 178 Ampere-hour rating (AHR), 300 Amperes, 287 Atomized, 217 Atoms, 285 Axle bearings, 437^38 Carburetors, 217-226 Carcass, 421 Casing, 421 Center electrode, 258 Chain-and-sproket drive, 355-357, 359 Charging system, 3, 301-302 Choke system, 223-224 Circuits, 288-289 Clamping screw, 34 B Cleaning: of 2-stroke engine, 94, 101-102 Back pressure, 207 of 4-stroke engine, 117 of lower end engine, 160-163 Balancing wheels, 430 Ball pein Battery, hammer, 26 Clutch, 330-332 249 Battery charging system, 308-310 Battery charging voltage, 303 Battery operation, 297-300 Battery rating, 300 Battery safety, 13-14 Bearing lining material, 156 Bearings, 155-156 Bleeding, 187, 408-409 Bolts, height, 118 Capacitor discharge systems, 254-256 Carburetor overhaul, 244-247 47 Boost pressure, 210 Bore, 69 Boring bat, 99 Bosses, 78 Bottom dead center (BDC), 62, 152 Bound, 285 Box-end wrench, 20 Brake backing plate, 395-396 Brake fluid, 404 Brake horsepower (BHP), 71 Brake system, 4, 395-409 Break-in period, 100 disassemble and reassemble, 341-342 troubleshooting and servicing, 335 Clutch adjustment, 336, 339-340 Clutch repair, 336-338 Clutch screwdrivers, 18-19 Cold spark plug, 261 Collector, 292 Combination pliers, 24 Combination wrench, 20 Combustion, 2 Combustion chamber, 61 Combustion principle, 61 Compressed air, 1 Compression, 64, 376 Compression measurement, for 4-stroke engine, 113-114 Compression rings, 79 Compression Compression stroke, 67-68 testing, 90, 111 Condenser, 252. {See also Breaker point capacitor.) Conductor, 287 Connecting rod, 155 inspection and measure, 172-173 Break point capacitor, 274 Constant-velocity carburetor, 224-225 remove and replace, 278-279 Breaker bar, 21 Coolant, 197-198 Breaker points, 252, 270-271 Brushes, 316 Converting metric and english measurement, 32 Cooling systems: air, 193 INDEX 444 Cooling systems (Cont.) liquid, 193-194, 200-201 servicing and troubleshooting, 198-200 Eddy (CEMF), 317 currents Counter-electromotive force (CEMF), 303-306 Electric fan, 195 Crank Electric starting system, 3 pins, 151 Crankcase, 149 Electrical accessory systems, 3 Crankcase compression phase, in two-stroke engine, 64 Electrical system, 3 Camshaft, 85 Electricity, Camshaft timing, 115 Electrolyte, Crankshaft, 61, 149 inspect and measure, 170-171 287-290 297 Electromagnetism, 290 Electron theory, 285 Crankshaft intake phase, in 2-stroke cycle, 64 Electronic torque wrench, 22 Cross, 358 Electrons, 285 Countershaft, 347 Electronics, Crown, 330 Current, 287 Elements, 285 Current flow, 285-287 Emulsion tube, 223 290-292 Emitter, 292 Customary system, see English measuring system End-cutting pliers, 25 Cylinder, 61 Engine, 2-3 Cylinder head, 66, 81-82 lower end servicing, 160-167 Cylinder measurement: lower end troubleshooting, 159-160 for 2-stroke engine, 103-104 Engine for 4-stroke engine, 135-136 Engine size and performance measurements, 69-72 English measuring system, 31-32 Cylinders, 75 parts, 61-62 Exhaust phase, 2-stroke engine, 64 Exhaust port, 66 Exhaust stroke, 68 Exhaust systems, 3, 206-210 Exhaust valve, 66 Dead-blow hammer, 27 Expansion chamber, 207 Deglazing, of 2-stroke engine, 97-99 Desiccant, 292 Extension, 22 Diagonal pliers, Dial indicator, Extractors, 54-56 25 39^2 Die stock, 53 Diode, 291 Face, 66 Disassembly: of 2-stroke engine, 93, 101-102 Fasteners, 47 of 4-stroke engine, 115-117, 129-130 of lower end engine, 160-163, 168-169 Feeler gauge, 43^4 Final drives, 353 289 Disc brake caliper, 416-417 Field, Disc brakes, 399-400 Film, 177 Displacement, 70 Fire extinguishers, 11-12 Double Fire prevention, 11-13 taper, 221 56 Drive chain, 362-365 Drive train, 4 Fixed jaw, 34 Driveshaft, 347, 358 Flywheel, 61 Drum Flywheel magneto, 252-253 Dowel pins, 404 Dry sump, 178-179 Dynamic timing, 272 Dynamometer, 71 brakes, 395, Float bowl, 219 Floating position, 307 Fouled spark plug, 260 Frame, 4, 369-374 Four-stroke cycle engine, 66-69 INDEX Four-Stroke cycle engine (Com.) cleaning, 117 compression measurement, 113-114 cylinder measurement, 135-136 disassembly of, 115-117, 129-130 inspection and measurement of, 117-121 piston measurement, 137-139 reassemble, 146-147 upper-end troubleshooting, I ISO (International Standard Organization), 51 Idle speed, 238, Idler, 242-243 328 Idler geais, 347 Ignition system, 3, 249-261 268-275 servicing, 1 1 troubleshooting, 265-275 Four-stroking, 235 Four-wheel machine, 1 Ignition coil, 249, Ignition switch, Free electrons, 286 274 249 Free length, 119 Ignition timing, 256, 271-272, Free play, 360 Impeller, 194 Friction, In-line, 177 151 pump, 190-191 Injection Front suspension, 374-376, 380-386 Fuel system, 3 Input shaft, 347 Fuel systems: Inspection: carburetors, servicing, of 2-stroke, 95-96 217-226 of4-stroke, 117-121 236-241 troubleshooting, 233-236 Fuses, 323 280-281 Insulator, 287 Intake port, 66 Intake stroke, 67 Intake valve, 66 Integral gears, 347 Galleries, 182 Gasoline flammables, 12-13 Gauges, 42^4 Gears, 327-330 Grade markings, 52 Ground circuits, 293 Ground clearance, 372 H JIS (Japanese Industrial Standard), 51 Journal, 149 Jumper wire, 294 Keys, 58 Hammers, 26-27 Hand tool safety, 7-10 Keystone ring, 80 Kickstarter, 353 Harley-Davidson, 154 Head, 78 Headlights, 320-321 Heat range, 261 Helicoils, 54 High reluctance, 289 High-tension system, 253 Hollow-head screws, 47 Horn, 323 Horsepower, 71 Hot spark plug, 261 Hydraulic disc brake caliper, 409 Hydraulics, 399-400 Lands, 78 Lapping procedure, 122 Lateral runout, 427 Layshaft. 347 Leading shoe, 398 Lifting and carrying rules, 6 Lobe height, 118 Locking pliers, 26 Loop scavenging, 65 Low reluctance, 290 445 INDEX 446 Low speed, 223 Ohm's law, 288 Low-tension systems, 254 Oil Lubrication systems, 3 Oil injection, 182 2-stroke engine, 182-186 filter change, 188-189 One-piece crankshaft, 165-166 4-stroke engine, 178-182 One- wire servicing of, 186-187 Open troubleshooting areas, 187 Open-end wrench, 20 Opposed cylinder arrangement, 154 M 289 circuits, circuits, 288, 293 Output shaft, 347 Overrunning clutch, 317 Owners manual, 27 Machining: 2-stroke engine, 97-100 4-stroke engine, 121-128 Machinist's precision steel rule, 32-33 Magneto ignition systems, 252-254 Magnetic poles, 289 Magnetism, 289-290 Main jet, 222 chart, 29 Master cylinder, 400-402, 407^08, 414-^15 Matter, 285 Measurement of 4-stroke engine, 117-121 Measuring systems, see English measuring system; Metric system Measuring 27 Permeability, 290 Phillips screwdriver, 18 Mainshaft, 347 Maintenance 288 Parallel circuit, Parts cleaning, 34-44 tool, Mechanical drum brakes, 407, 410-413 Mechanical voltage regulator, 306-308 Meter, 31 Metric system, 31-32 Micrometer, 37-39, 42 Millimeter, 32 Monoshock design, 377 Moped, 1 Motor armature, 317 Multimeter, 295-296 Multiplate clutch, 330 Mutliple disc wet clutch, 330 Pilot speed, 223 Pin hole, 78 Pinion gear, 317 Pinion shaft, 358 Piston clearance, 78 Piston pin, 81 Piston rings, 79 Piston seize, 79 Piston skirt, 79 Piston slap, 79 Piston measurement: 2-stroke engine, 105-107 4-stroke engine, 137-139 Piston port, 64-65 Pistons, 61, 75-76 Pitch gauges, 52 Plastigauge, 166 Pliers, 24-26 Points checker, 272 Positive plate, 297 287 349-353 Potential difference, N Needle nose pliers, 25 Negative plate, 297 Power Power Power flow, stroke, 68 tool safety, 10-11 Precision insert, 156 Nozzle, 221-222 Pre-ignition, 261 Nucleus, 285 Preloading, 40 Nuts, 49-50 Premix, 182 Primary choke, 222 Primary drive, 330 Off-road riding, Ohm, 287 1 troubleshooting and servicing, 333-335 Primary wire, 253 Priming the pump, 187 Propeller shaft, 358 INDEX Service rating, 178 Set screws, 47 Radial runout, 427 Shaft drive, 358-359 Radiator, 194 Shallow socket wrench, 21 Shift mechanism, 353 202-203 Radiator pressure cap, 195-196 Rake, 373 drain and debug, Shoe brakes, 396-399 Short circuits, 293 Shunt winding, 307 Rachet handles, 21 78 Rear suspension, 377, 387-390 Skirt, Reassembling: Slide caliper, 34—35 2-stroke engine, 99-100 Sliding gears, 347 4-stroke engine, 126-129, 146-147 Sliding T-handle, 22 of bottom end, 174-175 Slippers, 78 of lower end, 166-167 Small-hole gauge. 42-43 Snap-ring pliers, 25 Rebound, 376-377 Snap 303 Rectifier, 301, Reed and Prince cross-slot screws, 18 Reed valve, 64—66 Relay switch, 319 Resistance, 287 Rim, 430 Ring belt, rings, 56-57 Society of Automative Engineers (SAE). 178 Socket drivers, 1-22 Socket wrench, 20-21 hammer, 26-27 Soft-face Solid-state current limiter, 306 Spark plugs, 256-261 78 Ring gear, 371, 358 remove and Ring grooves, 78 servicing, 268 replace, 276-277 Road horsepower, 71 Spark plug cables, 273, 282-283 Rocker arm, 67 Rotary valve, 64—65 Specifications, Specific gravity, 308, 311-312 27-29 Rotating magnetic rotor, 253 Speed adjustments, 238 Rotor pump, 180 Speed handle, 21 Ruler, 34 Splines, 58 Spokes, 427^29 Spider, 358 Splined gears, 347 Spread, 156 Sprockets, see Gears Saddle bore, 165 Stamped steel frame, 369 Starter, 223-224 Safety: in the shop, 5-7 in using hand in using power tools, 7-10 tools, 10-11 Starter motor, 315 Starter/generator, 315 315-320 while working on batteries, 13-14 Screw extractors, 54 Screw thread inserts, 54 Stem, 82 Screwdriver sockets, 22 Stemming Screwdrivers, 17-19 209 Stoplight, 321-322 Street motorcycle, Secondary wire, 253 Self-actuation principle. the valve, 124 Storage battery, 13-14 274 circuit, Steering system, 369-374 Stinger, Screws, 47 Secondary Starting system, 396 Semiconductor, 287 Stud extractors, 54 Separators, 298 Sttids, Series circuit, 288 Series resistance, 274 Service manuals, 27-28 1 Stroke, 69 49 Superbikes, 1 Suspension, 374-382 Suspension systems, 4 447 INDEX 448 u Tailight, Unified National Coarse (UNC), 51 321-322 Taps, 52-53 Unified National Extra Fine (UNEF), 51 Telescoping gauge, 42 Unified National Fine (UNF), 51 Test light, 272, 294 Universal joint, 22 Test ride, 100 Thermostat, 196-197 Threaded fastners, 47-52 metric and english systems, 51 Three- wheel machine, Throttle valve, 1 Valve cutting, 123-126 Valve faces resurfaced, 142-143 220 Throws, 149 Timing light, Valve guide replacement, 140-141 273 Valve lapping, 122 Timing marks, 115 Tire pressure and markings, 422^25 Tire repair, 425 Tires and wheels, 4 Tires, 421^25 Top dead center (TDC), 52, 62 Torque, 71, 327 Torque multiplication, 327 Torque wrench, 22 Tracers, 293 Trail, Transmissions, 347-353 292 Tread wear indicators, 421 Truing, test, 427^28, 433-434 Tubular frame, 369 Turbine, 210 Turbocharging, 210-213 Turn signal, 322-323 Twin-shock design, 377 Two-stroke cycle engines, 62-66 cleaning, 94, 101-102 compression measurement, 91-92 cylinder measurement, 103-104 disassembly of, 93, 101-102 inspection, 95-96 piston measurement, 105-107 Valve spring compression, 116 Valves, 82-83 Valves guide, 83 Valves seat, 83 Valves springs, retainers, and seals, 84-85 Vaporization, 217 Vernier caliper, 35-37 Viscosity, 178 Voltage, 287 Voltage regulator, 301, 303-305 w Washers, 50 Wastegate, 213 Wear bars, 421 Wet sump, 178-179 Wheel assembly, 425-427 Wheel hub assembly, 430-433 Wheel rim, 435^36 Wheelbase, 373 Wiring diagrams, 292-293 Wrenches, 19-21 reassembly, 99-100 top end servicing, 93-100 top end troubleshooting, 89-90 upper end assembly, 108-109 144-145 Valve spring, 66 Venturi, 218 1 Trailing shoe, 398 Transistors, Valve mechanism of 4-stroke engine, 131-134 Valve seat and resurface and Variable venturi, 220 373 Trail bike, V-twin engine, 154 Zener diode, 292 0-8359-4669-X