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Replacing a Honda CB400 alternator

This is a tutorial about how to change an alternator of a Honda CB400N.
It's really not a complicated job, and it will provide you a good guide.

Overview of the tools you need:

Nr. 10 Allen-key
Oil drain plug, 20mm with 1.5mm thread
(Cheap replacement for official flywheel extractor)
Philips screwdriver
10mm nut with ratchet
Ratchet with 1/2" head
Torque ratchet
Impact Hammer (with "sand" in it)


Off we go!

Step 1. Remove the gear shift lever

Step 2. Remove the flywheel cover, you will now see the flywheel and the pickup coil or pickup sensor.


Step 3. Remove the center bolt by blocking the flywheel with the 1/2"head ratchet. I forgot to take a picture of that, but the idea is that you have the two holes horizontally, stick the ratchet head into the left hole and stop it from going lower by pointing the handle downwards to the ground. you may need a block of wood or a few bricks to make the sufficient height. Let me show it through my mad artistic drawing drawing skills, since interpretive dance looks rather silly.


Now I do not have the money for specialized tools, so a quick Google search lead me to a really nice and cheap solution. A simple oil drain plug that costs around €7. The width is 20mm and the thread height is 1.5mm

Step 4. Insert the plug and screw it all the way in. Check if you have enough clearance left! If not, remove the plug and add some washers.

Step 5. Insert the Allen-key and you can use the 1/2" head ratchet again to hold it down, but i am a strong believer in intertia so a few good whacks with my trusty sand hammer did the trick in half the time.


Step 6. If all went well and the Allen-key did not fly through your neighbour's window, then the flywheel has come loose.

Please keep en eye on the little flywheel pin or wedge. It holds your flywheel in one fixed position with your crankshaft and if you lose this, you turn your motorcyle into a giant paper-weight!


By removing the flywheel you have exposed the alternator that is basically a bunch of wires in coils providing power to your lights and ignition. You should know that otherwise you would not open up this part of your engine, ofcourse.

Step 7. Disconnect the connector plugs. These are located under the fusebox.

Step 8. Remove the three bolts with the philips head and the two bolts of the pickup coil with the 10mm head. I have circled the ones you should remove. Do not, and I repeat, do not remove the bolts that I have crossed through!


Also note that there is one philips bolt that has a washer. Remember the spot and do not forget to put the washer back when mounting the alternator back in!


Step 9. When you have removed all the bolts, carefully take out the alternator. It can be a little stuck, but wiggle it a little and it will come loose. With the alternator in your left hand, slide out the rubber wire holders located as shown below:


If your cable is now free, you can safely remove the entire contraption and start measuring with your multi-meter!

Putting it all back together

Step 1. Carefully slide the alternator back on its fitting, making sure that the holes of the bolts align with the screwholes in the engine block.

Step 2. Screw the three bolts back in with the Philips head. Remember the one with the washer? Then mount the pickup coil with the two bolts that have the 10mm head. Tighten both so, that cannot run loose. There is probably a set torque for it, but you know probably best what is tight enough.

Step 3. Fit the rubber wire holders back in place and connect the connector plugs.
Now is the time where you realized that you have seen that silly little wedge somewhere but cannot find it back. Go find it, it is the difference between you having an awesome time on your motorbike and sitting on the couch sulking because you did not read my warning earlier. If you have the wedge, carry on!

Step 4. Put the wedge in the slot on the crankshaft axle and fit the flywheel back on.


Step 5. Give the flywheel a few little taps on the center with the plastic hammer so it sits properly and put the center bolt back in.


Step 6. Now here comes another tricky bit if you lack proper tools like me. To tighten the center bolt securely and according to specification, you need to find a way to lock the flywheel again. I have done the following: Get a good piece of wood and place this against the footrest. Now take the small ratchet and stick the 1/2" bit into the flywheel hole and place it perpendicular to the wood. Look at the picture below:


When you have set your torque to the right setting, your starting point should look like this:


Set your torque ratchet to 80 foot pounds


Step 7. Now make sure you increase the pressure slowly in order to keep your teeth in. Keep building pressure till you hear the ratchet "click". At this point you have applied enough torque on the bolt.


Note: This is a duplicate article.

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