Engine Noise

[Frankencelery]

I've been lucky enough to be able to ride my 250SX for a few years without having to do any engine work. Now it's making a fairly loud top end clicking noise at idle. Assuming it was the valve adjustment, I got out my service manual and adjusted them to .003-.004 like it says, but no difference in the sound. It's most obvious at idle. I'm thinking it must be a loose timing chain, but the adjuster is...well....non-adjustable. What to do? Do I have to just assume the timing chain needs replaced?

[Russell 350X]

It's the timing chain. My 350X did the same thing. Sometimes those tensioners get gummed up. Pull it out and clean it with some brake clean and see if it still does it.

[Woodsrider]

A mechanic friend of mine explained a way to verify if the noise is the cam chain or not. I have yet to try this because I have too many projects on the go....

Remove the auto-tensioner and then use a PLASTIC pen to push the tensioner guide against the cam chain while running the engine. If the noise stops, it was your chain...then you need to determine if your auto-tensioner was the problem or if you need a new chain. At least this would eliminate other possibilities.

[Frankencelery]

Thanks, I'll check that out. I was wondering if there was anything to clean in that tensioner assembly. I can try what both of you suggested at one time. Funny thing...it doesn't always make the noise. Today a buddy and I went to an ATV park and rode hard for 4 hours, and I never heard it. Seems to be worse when it's cold.