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Valves at zero clearance.

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My bike (2002 YZ250F) recently has been losing valve clearance very fast after an adjustment, It's now to the point where the bike will not even start after about 4 days worth or riding. I just checked my clearances again and all three of my intake valves are at zero clearance. Almost all of the compression is going right back into the intake. What am I going to have to do to keep the valves from going out of spec so fast? Do the valves themselves need replacing? Or is it something else that needs to be redone?

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Sounds like its time to replace. Don't do any more adjustments. Once they begin to get tight quickly they are typically stretching or rolling at the seat and if you continue to re-adjust you run the risk of breaking a valve and causing major damage. Tear it down and put some new parts in it. I would suggest a new piston, new timing chain, new intake and exhaust valves, valve springs, valve guides and valve guide seals. If you do it right you should get several more years of maintenance free ridding. The valve guides may be optional depending on whether they are still in spec or not, they are a pain to install and then you have to ream them to the correct size. Do a lot of measuring on tolerances. Cylinder size, check for out of round, clearance at the rod bearing, etc etc. You may have to have the valve seats re-cut for the new valves. You might consider sending the head to a reputable shop. Let us know how it turns out.

Good luck!!

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Yup, once they start losing clearance that quickly, it's time for new ones. I really doubt you'll need guides though, they almost never do. And the piston on my '01 was perfect, too. Just replaced rings, timing chain, valves and springs.

But, I have some bad news. If nothing changes soon, your bike will be down for a while. I tried buying Kibblewhite valves and springs, but no one from the TT Store to White Bros (the distributor) to Kibblewhite themselves had them in early January, or had any idea when they would. So, I ordered OEM stuff from Yamaha and found out it was backordered too. Ordered 1/7/05 and just got the last of it today. So off it went to the machine shop. Now it turns out they never ordered the intake springs, and Yamaha has no release date for their availabilty. :cry:

Wasn't Japan the country that perfected modern inventory controls?

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My bike (2002 YZ250F) recently has been losing valve clearance very fast after an adjustment, It's now to the point where the bike will not even start after about 4 days worth or riding. I just checked my clearances again and all three of my intake valves are at zero clearance.

Just comparing notes between brands. About how many hours did you have on the bike before the first valve adjustment and how many adjustments have you made? Thanks.

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Just comparing notes between brands. About how many hours did you have on the bike before the first valve adjustment and how many adjustments have you made? Thanks.
My '01 went until last summer before it had its FIRST valve adjustment. Wasn't required up to that point. Between then and now, it's needed 2 more. I'm currently doing a top job because of that at about 450 hours.

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I agree that it is definitely time to replace the valves. There are two options: Replace with stock titanium valves or with Kibblewhite stainless valves and KW springs. More expensive, but some say better longevity. I went with THE KW setup, but only have a few hundred miles on the new setup so it's too early for me to provide an opinion on them.

Any comments on which way to go from the lurking experts?

RH

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