'98 YZ400 Timing Chain Problem

It seems my timing chain keeps jumping a tooth. I get it fixed but soon after it does it again and runs like crap. (or not at all)

What would cause this to happen all the time ? :D

The valves were adjusted and were fine and the carb has been rebuilt also.

The bike was sitting for a long time before. (9 months)

Any suggestions would be greatly appreciated ! :D

Sounds like worn timing chain and possibly gears. I would replace them as a set. also check the chain adjuster.

Check the gear on the crank. If its shot then a new half crank is in your future

Sounds like worn timing chain and possibly gears. I would replace them as a set. also check the chain adjuster.
I always get a chuckle out of it when someone makes this recommendation. It would cost $600 to do that. The cam sprockets are serviced only by replacing the cams, and the crank sprocket is cut directly on the left axle of the crank.

Fortunately, it seems nearly impossible to wear out the cam sprockets. Unfortunately, the same cannot be said for the one on the crank. This is the single best reason to replace the cam chain on a fairly regular basis; so that it won't prematurely wear the crank gear off.

Yamaha does, however list the two halves of the crank separately, if that turns out to be necessary.

Yamaha does, however list the two halves of the crank separately, if that turns out to be necessary.

What's your suggestion on this situation? Replace the WHOLE crank of just the half....doesn't that entail getting it pressed correctly? :D

What's your suggestion on this situation? Replace the WHOLE crank of just the half....doesn't that entail getting it pressed correctly? :D
Yes, it does, and that involves shop labor, so in the end, I'm not sure which would be less costly. Another detail is that to be technically correct, you should not reuse the crank pin (press it out of one crank and into another), and you shouldn't use a used bearing on a new crank pin, and... you see where this is going, don't you?

I would check the TT store for a new crank, is what I would do. Their OEM parts prices can only be beat if you own a dealership or have a sponsorship.

I would check the TT store for a new crank, is what I would do. Their OEM parts prices can only be beat if you own a dealership or have a sponsorship.

Good deal. Just trying to prepare to do things correctly if/when the day comes. :D

You might try replacing the chain 1st. Chain is like $35. Crank is major $ and time. If its a 98 the chain is probably stretched out farther than the tensioner can compinsate for. yea the sprockets may be worn. But what do you have to loose by swaping out a new chain. What $35 if the sprockets eat the chain. Still cheep compared to a new crank / splitting the cases.

Well, of course, the thing to do is remove the flywheel and stator to inspect the sprocket's condition, then decide what to do from that point.

Well, of course, the thing to do is remove the flywheel and stator to inspect the sprocket's condition, then decide what to do from that point.

Come on now. Let's just speculate on the internet and make him throw all kinds of time and coin at the problem in a haphazard fashion. :D:D

Chain is like $35.
The chain for my '03 was $20 with an ignition over gasket and California sales tax. It's too cheap no to do once in a while.

Thanks for all that info !! I'm going to try just the chain first and go from there. :D

The chain for my '03 was $20 with an ignition over gasket and California sales tax. It's too cheap no to do once in a while.

I just picked up a timing chain for my 99 WR400 from my local dealer - $38 OTD. Probably cheaper here on TT, but after you pay shipping and handling (&%$#@! is that :D ), it's more expensive.

I just picked up a timing chain for my 99 WR400 from my local dealer - $38 OTD. Probably cheaper here on TT, but after you pay shipping and handling (&%$#@! is that :D ), it's more expensive.
My $20 cost was a no-discount buy at a dealer, too. Like a lot of things, the old stuff costs more than the current product.

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