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valves waaaaaay to tight but still runs good?

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so the valve clearence for a wr250f is 0.17, ~, 0.22 mm for the exhaust and they are at about 0.13

still starts first kick and runs fine.., how can the bike still run with it out this much

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That's too tight, if you measured correctly. It will run that way for a while, but eventually you''l burn the valve seat. Re-shim it before you mess it up.

 

Just re-measure again with the cam lobe opposite the valve to be sure that you weren't on the lobe's ramp when you took the last measurement. You don't want to fix something that isn't broken. 

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The exhaust valves are just opening a little sooner and a little wider than spec, otherwise you are getting combustion so you don't notice. Time for new shims, as you know.

Edit: I didn't think to recommend measuring again, but that makes sense.

Edited by Dragon67

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Yea just because its tighter then it SHOULD be, doesnt mean they wont fully close at some point in the revolution of the cam. The bigger issue is that they are closing up some clearance-wise. Exhausts on these bikes arent usually known to go...at least before the intakes unless the intakes only were done when the exhausts were still fine. Howd the intakes look?

Edited by J_WR2fitty

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If there is ANY cold clearance no harm no foul.  Like mentioned it is a sign things are wearing.

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If there is ANY cold clearance no harm no foul.  Like mentioned it is a sign things are wearing.

 

Not true.  Once hot there is even less clearance.  This can easily burn a valve if the heat can not transfer to the seat effectively.

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on some motors ,, but not this one,  they get looser, try measuring it hot sometime.   Time on the seat is important and it's less than ideal to run them out of spec, but it won't burn a valve.

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Not true.  Once hot there is even less clearance.  This can easily burn a valve if the heat can not transfer to the seat effectively.

 

I concur. The head, being aluminum, has a higher rate of thermal expansion than the valves. Logic suggests they get tighter with heat, however, I could be wrong, it's happened before. 

Edited by singletracmind

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get it hot, pull the valve cover and check them, check again when it cools down.   I can measure a difference from a 40f to a 75f shop.

Edited by highmarker

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Yea just because its tighter then it SHOULD be, doesnt mean they wont fully close at some point in the revolution of the cam. The bigger issue is that they are closing up some clearance-wise. Exhausts on these bikes arent usually known to go...at least before the intakes unless the intakes only were done when the exhausts were still fine. Howd the intakes look?

intakes were perf

were is a good place to buy shims guys?

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If there is ANY cold clearance no harm no foul.  Like mentioned it is a sign things are wearing.

highmarker is correct. I got in a heated debate about this very thing with a TT moderator, so I went out in the garage and got the engine good & hot, then measured them. Then went back on TT and apologized to the moderator for being wrong and calling him out. The clearance does increase with heat, but still don't run them tighter than what the manual calls for. They still need to "seat" for a certain length of time to shed there heat into the valve seat area, so that they don't burn up.

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Well I have heard that the bike should not of been ran for 24hrs prior to cold valve check. Seems excessive, but maybe its to be sure.

 

Far as them having more clearance hot...does seem odd. But if you remember, a lot of times its said that COLD start issues is usually the sign of bad valves....not so much for hot. Least from what I have seen in the past.

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Why bike with tight (zero'd) valves will start hard but run ok and restart warm all day. Take along break in the wind, bike cools off and it won't start.

 

up thread some said alum head expands with heat, yes !   valves get pushed farther toward the crank, and cam towers push cam farther up the other way,  The the valves, buckets, shim etc just float in the middle so gain clearance.   I have 2 bikes that spec ,002", so seeing spec like .006 and .011 on my honda seems loose to me. The cam duration in these bikes isn't so long that the closed seat time is really compromised to the point of burning a valve on few thousandth of lash difference.  It's not good to run them too close to zero because they may move during a ride have have you stranded, but not with a burnt valve. 

Edited by highmarker

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