yz426 Front Sprocket Question

2 replies to this topic
  • MaDgamEr

Posted June 13, 2007 - 07:53 PM


Hey guys/gals,

Just finishing up a complete rebuild of a 2000 426 I bought from a friend. So far so good, as the entire project has come together very nicely.

I have replaced every single bearing on the bike chasis, wheels, painted the frame. Rebuilt the forks and rear shock. New piston, rings, timing chain, completely fresh valve train, hot cams exhaust cam. While I was getting the new guides pressed, I ended up porting and polishing the head. Dismanteled and cleaned the carb, did the BK mod.

So far, so good. The bike absolutely tears at any RPM range. Now this brings me to my question...

When I was putting the front sprocket back on, I noticed that the drive axle was quite stiff to turn by hand once the sprocket nut was tightened down any more than hand tight. Once I put the chain on, it was fairly easy to turn by spinning the rear wheel (as you would expect), but you could still feel some tension. Is this normal?

Forgive me for asking this question if it seems a little on the dumb side, but after spending 11 years on the sportbike side of the world, this is the first time I have felt any "tension" in a countershaft with the sprocket torqued properly, and bike in neutral.

Thanks for your help, and thanks for having such an awesome forum that has already helped me SSSSOOOO many times on this project. I love the search feature... hence only a few posts so far.

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  • grayracer513

Posted June 13, 2007 - 08:36 PM


There's an inside and an outside to the front sprocket. One side is flat, and the other has a wide groove cut into it. When most people look at the sprocket, they can't see a reason for it to need to go on one way or other, and the grooved side looks way cooler.

But the dust seal over the output shaft seal hangs out beyond the collar that the sprocket bolts up to, and if you put the sprocket on grooved side out, the dust cover rubs on the sprocket. The flat side goes out. Don't ask me how I know this.

  • MaDgamEr

Posted June 14, 2007 - 01:52 AM


Thanks for the quick response Gray, and I double checked the sprocket. It is in fact installed with the groove towards the collar (engine). I did however notice that the axle oil seal is not quite driven flush with the engine case... I can't see this being a the cause since the seal is still in further than the collar. Should I be concerned about this? Not sure if I should just forget about it, or if this is going to be the source of a bigger issue diwn the road.

Would it be worth pulling the oil seal and collar out and replacing them?

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