'00 YZ 426 CB drive gear key - clack, clack, clack

God awful rattling sound at idle last weekend. I was concerned that I'd lost a radiator bolt, or that the head wasn't receiving oil or something.

I did some reading here, lead me to suspect the crummy key securing the counter balancer drive gear to the crankshaft.

I removed the right side crank case cover last night, and sure enough, the counterbalancer drive gear had 10-15 degrees of slop, it was easy to "clack" it back and forth by hand. It makes the exact noise I was hearing from behind the water pump with the bike idling. Also, the nut on the crankshaft was surprisingly loose.

I am glad I didn't ignore the noise.

So I ordered a new key, lock washer and crankcase cover gasket from bikebandit.com. I'll have to pull the clutch assembly in order to replace the key.

To unfasten the nut holding the clutch, should I...

a) get the Yamaha clutch holder tool

:thumbsup: jam a screwdriver in the clutch drive gear

c) put the bike in gear and block the rear wheel

Anything else I need to do while I'm in there? My plan was to just a loc-tite a Yamaha key in there instead of fashioning a new key from longer thicker stock. Is this stupid?

Many thanks for your wisdom...

You can do ©, or you can just hit the clutch hub nut with an impact wrench. A few guys have had problems with new Yamaha keys failing as well, so you might want to go buy some key stock and cut your own key just to be safe. Better to only have to tear it apart once. Or, if you have a bunch of loose cash laying around, you could buy a right side 01 crank that has a splined CB gear.


So much for only tearing it apart once. After installing my new key and reassembling the bike, I found that I could not shift gears. I inadvertently let the shift shaft slot slip off the roller. Since the shift shaft is held in place by the right side case cover, it all had to come back apart.

I located a clutch holding tool, and it was excellent for installing the clutch hub nut, allowing me to torque it properly. However, it was of no use for removing the frozen clutch hub nut. A borrowed electric impact wrench did that job nicely.

Once properly reassembled, my bike started right up, ran much quieter (just the normal level of YZ 426 clatter, no more violent clacking from the CB drive gear), and clutched and shifted smoothly.

Thanks for your help!

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