Intermitent clunk

This evening I was riding my 1998 YZ400 and started to hear an intermittent knocking noise. It is not a piston knock too intermittent. Put it in the garage and took covers off and found the decompression lever was stuck open. So I started it up again to see if that had anything to do with it and noise still there. Shut it off right away. Bike starts just as easy as always. Shifts fine too. Not sure wear to start. Going to pull oil filter to look for trash. Oil was full and clean too. Thinking possible cam chain or valve adjustment or even chain tensioner. Just looking for alittle direction. Thanks.

Wild stab in the dark: check your lower shock bearing. They are first to go bad and often make a clunk or thunk sound just lifting in a garage. If you're hearing noise with throttle off over rough terrain that clunk clunk could be it.

 

Best of luck finding the noise.

The 400 and the 200 model 426 have a square key that achhors the balancer drive gear to the crank instead of splines as on the later ones.  If the crank nut works just a little loose, the balancer gear can start rattling back and forth on the crank/key.  Something to look at. 

Thank you gentlemen I will definetly check both of those. Anything better to do than putting another oem keyway maybe some different material if it is that? Upgrade to spline type maybe? Thanks again.

Upgrading to the spline type gear of the later models would require changing the crank, but that would mean a 426 crank in your case.  Then you'd set off a cascade of other required parts to make the crank match the rest of the engine.

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