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BrandonW

Valve Adjustment gone wrong....

5 posts in this topic

Friend of mine has a 2000 XR650R, and he went to do a valve adjust on it for the first time.

Here is what we know:

He is not sure that he was at TDC when he did his first "adjustment"

He thinks that he might have rotated the engine about 1/4 of a turn in the wrong direction when he was trying to find TDC.

He has gone back in a number of times, and is sure that he has has the process down correctly, but the bike is now VERY HARD to turn over; it barely runs, and when it does he hears some knocking and pinging to the extent that he he just shuts it down.

He has not loosed the cam tensioner chain, so the timing should still be the same.

Any ideas of what he might be dealing with?

Thanks,

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Without any other info, it sounds like the cam chain tensioner has moved, this happened while turning the engine over in the wrong direction. Let me say this, any cam chain driven engine should NEVER be turned the wrong direction.

You will need to start with getting the chain tensioner re-set, and hopefully there was no damage. You also need to make sure the chain hasn't "skipped' a tooth, I suggest a factory manual.

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The auto decomp system on the big XR is cam-mounted. If you turn the engine backward during valve adjustment, it can throw off the decompressor, resulting in an out-of-spec valve clearance. If the clearance is too loose, it would be hard to start and noisy.

If the shop manual doesn't advise it already, pull the sparkplug to allow a more accurate crank rotation by hand. Checking/resetting the tensioner is fairly quick, too.

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Awesome guys! I thank you for your input. I agree that something has happened to his timing, and turning the engine backwards and "jumping a tooth" on the cam sounds like what might be giving him headaches.

Thanks for the help guys, I will pass this good information on.

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Check the exhaust valve on the right side for extreme clearance. This is the valve that is affected by the autodecomp. Adjust it with the crank after TDC on the firing stroke to minimize the autodecomp affecting it.

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