Mystery Noise

When riding this afternoon, I noticed increased noise (sounds like piston or cams?) coming from what appears to be the top of the cylinder head around the camshaft on the right side of the engine only - left side is quiet. It sounds like metal rubbing at approx. the same RPM as the engine-maybe slightly less. Noise gets slightly louder at higher RPM's. Bike is 01 426 w/ about about 3 hours max on it w/ BK mode and runs freakin' unbelievable!! Anyone else seen this symptom? Also, anyone know a GOOD Yamaha mechanic in the Dallas-Ft. Worth area? I've pretty much lost confidence in reliable service w/ the shops I've visited. Thanks to all fellow Thumpers!!

Can you clarify "rubbing"? Does it sound like the usual valve/lifter noise that you hear in a 4-stroke only louder, or does it sound like a "bad" sound? I have noticed that this motor is very noisy when compared to other 4-strokes that I've heard as far as the valve/lifter noises go (clicking, etc..) but I don't hear anything alarming (mine is also an '01).

My friend just had what may be the same problem. His was more noticeable at lower RPMs. A couple guys from this forum said it might be the primary drive gear or cb gear. I doubted it, but they were right! He pulled the right case cover off and the primary gear was loose. A little red lock tight and a little torque and the noise was gone. He just did it last week. I guess it is common. Look up cb gear on the search for more info. good luck!


Was this an '01 with the loose cb gear?

The noise does not sound like valve or lifter noise; it's like the sound of metal rubbing together like a loud piston ring or something. Since it's on the right side of the motor I suspect it might be the CB gear detailed in the other posts. Thanks for the responses and I'll have a look at it.

It is most likely NOT the CB gear. The '01 crank was improved with a spline drive, not the failure prone key drive.

[This message has been edited by Scott F (edited September 25, 2001).]

After searching and reading through the other posts, it doesn't appear that it is the CB gear (o1 model) although the sound (and symptom) appears to be identical to those posts w/ CB gear and nut loosening issues. I suspect the only way to find out is to remove the right side case and inspect carefully. If you guys have any other suggestions, I would appreciate it.

hey guys, the Primary gear can get loose on an '01.

It's worth taking a look to see if the nut is loose. That could lead to some unpleasant damage.


Scott F '02 YZ250F < '01 YZ250F < '00 YZ426F < '99 YZ400F <'98 YZ400F


If your looking for a good mechanic, try giving Brian Story of SMS Racing a call, his shop is in Denton. 940-381-0737.

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