00 426 keyway & balance shaft - teardown help help

Good evening everyone:

I've been planning a tear down of my 2000 yz426f for over a year now. I finally found a few days (and motivation) to do it, and I am at a roadblock. I have the crankcase torn down to the point where i can remove the primary crankshaft nut, so that I can get to the keyway/key. I can't get the crankshaft nut off. The Yam manual says to put a piece of aluminum plate in between two gears to be able to remove the nut. All I'm doing it making a nice rolling imprint of the two gears on my aluminum plate. The gears just churn through the aluminum, which is better than breaking off teeth, i suppose. I was to the point of trying my clutchremoval tool to hold the gear, and figured that my exhaustion might be making me stupid, so I'll turn to the experts.

The whole reason I'm doing this is because my bike is making some godawful noise.

I don't feel any wobble or looseness in the crankshaft gear(s), which I expected to find, if the problem really is the keyway/key. However, I do find a little bit of play on the balancer gear/shaft. Not enough to say it's problematic, but just slightly. It seems as though the balancer isn't torqued on as much as it should be, the lock-washer is the only thing holding the nut on the balancer shaft.

Does anyone have experience (grayracer?) with if what I am seeing points me in one direction or the other? Tips on removing the crankshaft nut? Should I stop my assault on the crankshaft nut, or check the keyway since im in this far (i think i should to be safe).

I appreciate the help!


Get a bigger piece of aluminum, or a piece of oak. Or better yet, an impact wrench.

May as well look at it.

What Grey said - or even a penny, but definitely use an impact gun, it'll spin off effortlessly.

Thanks guys. Great help as always.

So after I got home from work today, I decided to give it another try. I first started by throwing a torque wrench on the crankshaft nut to see what it was torqued at. I hit 115lbs, and decided to stop (this was a counterclockwise-torque spec) I think someone put the nut on the crankshaft with an impact hammer the last time they were in my engine. hmm. Naturally, I turn to my impact hammer (I hate using an impact hammer on anything engine related, Im old fashioned)

Moving on, I continue to move toward inspecting.replacing the key. No key. hmm. Oh wait, the gear's actually cogged. No need for a key. hmm. Someone has already done some part swapping in my engine.

So, I retorqued the crankshaft nut(to 54ft/lbs), torqued the balancer shaft nut, and tore off my old gasket. I'll continue to reassemble tomorrow.

Guess it wasn't that big of a deal that I tear into my engine. I learned something though..I have no idea what parts are inside my engine. The guy I bought it from raced Pro AMA D14, and said he had the engine built in germany and shipped home. I guess it really was built in germany, with some substantial upgrades. The problem is that now I want to check my valves, and I know I'm not running standard Cams. I have no clue where to start for shimming checks.

Ahh well. The fun of owning a bastard bike.

I'd be interested to see what you guys have to say about my findings.

Thanks again!


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