Vibration Source?

Help! I have a 02 YZ426 with an engine vibration that increases with rpm's. It hasn't been abused and has had frequent oil changes and always a clean air filter. No smoke from the exhaust or knocking from the engine.

I've checked the flywheel and Zip Ty weight, the clutch basket nut and motor mounts.

Any ideas?

First, check it for any loose engine mount bolts. Then, we need to know if it was OK once, but started shaking recently, or if it's been like this since you've owned it. Have you done any work on the clutch or primary gears, and did the vibration start after that?

If either of the last two scenarios fit, you could have a counter balancer shaft out of time with the crank. The balancer shaft is supposed to create a out-balance vibration that opposes those created by the engine itself, so that the two cancel each other out. If the shaft is put in place out of position, it will make things worse, rather than better. You could also check the shaft for a bad (loose) bearing.

I'll recheck all the mount bolts (I did check the easy to get to ones and they were all tight. This time I'll do a better job and take the tank and skid plate off to check).

The vibration is a recent thing. I notice it more on the moto track than during woods riding because of the higher rpm's.

The engine and clutch are all stock and have never been apart. It really doesn't have a lot of time on it and I'm the original owner.

Stay tuned for a full mount check.


I'm interested to see what you came up with. Anything yet?


I rechecked all the engine mounts - all were tight.

Yes, there was no vibration awhile back, it seems to getting worse.

I've never had the engine apart, no clutch or primary gear work done.

While checking the flywheel and add on weight that they were tight I checked for play in the counterbalancer on the left side of the engine. There was a very slight amount of detectable play in it. I don't know if that indicates bearing wear or is it just normal slop in the shaft and keyways?

Where is the best place to check for the balancer bearing wear as you mentioned for the next place to check?


The shaft has a bearing on both ends. You just looked at the left end. The right is under the other engine cover, behind the water pump. One thing you may not have checked for in your flywheel inspection is to remove it and see what it has gathered up and stuck to its interior. If you've had a gear tooth drop off, or a bolt drop out of a retainer plate, it could end up stuck to one of the magnets in the flywheel. Might cause your problem. ?

Vibration that increases with speed is generally attributed to imbalance in the rotating mass. Greyracer has you on the right track of things to check. Have you noticed a sudden increase in the amount of metal in your oil filter or ferrous metal on your magnetic drain plug?

No, oil and drain plug are clean. I've had the 8 oz Zip Ty weight on it for the past couple of years and had no problems. I just rechecked it and everything was tight. I'm thinking about running without it next time I ride to eliminate it as a source.

Maybe your frame is cracked?

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