2000 yz 426 motor knock

2000 yz 426 has a motor knock. It sounds like its coming from the counter shaft balancer and water pump area. Any ideas.

It's a bad key on the crankshaft. There are two gears on the right end of the crankshaft. The outer one drives the clutch assembly, and is secured to the shaft with splines. Right behind that gear is another one which drives the counter balancer. That second gear is held in place on the shaft with a key. The key is the same part from the older YZ400F, leading some people to believe that's it's not strong enough to handle the increased "thump" of the 426.

The key cracks, deforms, or wears down, causing the counter balancer drive gear to have some slop in the crankshaft. This slop sounds like a fairly loud "clack, clack, clack" at idle, when the rotational velocity of the crank shaft is "pulsing". The sound goes away when you get on the gas, but it won't be long before the key fails completely, or the nut securing both gears to the crankshaft loosens to the point that something horrible happens in the right side of the crank case.

The cheap fix is to replace the key with either the stock part, or a longer, thicker piece of key stock.

The expensive fix is to replace the crank shaft and counterbalancer drive gear with the parts from a 2001 426, which used splines to secure the gear instead of the key.

Do you know if a 02' crankshaft will work? I've found one that has a good price tag on it. I have a 2000 426 with the same problem...I think. I haven't torn it apart yet, but it sounds like the same problem I have. I'd rather replace/update the crankshaft while I have it apart if this 02' crankshaft will work. Any info would be greatly appreciated. :thumbsup:

You can replace the right side of the crank with an 01 or 02 unit, but I'm not sure how much worked is involed in doing it. Send a PM to Hick, he'll know.

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