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CRF250X valves looser than spec, why?


12oclocker

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I'm doing the valve adjustment on my CRF250X, specs call for

intake: .005in +/- .001in

exhaust: .011 +/- .001in

My intake measures .004in, but my exhaust measures .014in on the right side, and .0135 on the left side. My question is, how did the exhaust valves get looser?? I seen valves get tighter as they seat, (like the intake did) but my exhaust valves going .003in looser? do people shim these things looser on purpose sometimes to lower the maintenance schedule during non competition use? or is something else going on maybe?

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so should I leave everything alone, and just check again later?, since the intake is technically in spec (only 1 thousands too tight), the exhaust being too loose is not going to hold my valves open, but maybe more wear on the valve train? I never rev this bike up anyway, it's eithor in a parking lot doing slow stuff, or commuting to the parking lot.

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Intake valves are the worry on Hondas. They will eventually get tougher to start as time goes on and the valves wear. Remember, when replacing valves (you're not at that point), you need to do the other stuff like springs, keepers, etc....

Exhaust being a little loose is something you can change and get into spec a lot closer, but it will not be as big of an issue. I would get them to .012, though.

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cool thanks guys, since the intake is in spec, I'll probably just check it again this summer after a few rides, It's not like I race the bike or anything, I barely rev it, its all slow parking lot stunts, I put a cooling fan on the radiator (honda had an optional fan kit for the x models I ordered) we'll see how much it changes next check I guess.

Edited by 12oclocker
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1. Measurements should be at nominal temps, room temperature. like 70F

2. Some air cooled engines won't like factory exhaust gap specs. They will leak when the engine warms up too much. I had one like that. I just gave it a tiny bit more than the factory spec, then it quit leaking. edit: or was it the intake valve? whatever, details lost in Time...

Edited by ReconRat
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Hi, It may be carbon build up from barely reving it. It might do you good to ride it hard once in awhile to blow the carbon out. The bummer would be shimming it then having the carbon blown out leaving no clearence.

Works the other way, a carbon build up anywhere in the valve train would reduce the clearances. Yes?

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Hi, Carbon build up on valve and seat will increase the valve to cam clearence because the valve is sealing against a layer of carbon. A good hard ride before and after practise may clear the carbon out. Extra clearance will not hurt anything but clearance increase and slight power decrease and with more clearance more ticking. The only worry would be if you continue to ride only at low revs then the carboning may get worse. Good Luck!

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Hi, Carbon build up on valve and seat will increase the valve to cam clearence because the valve is sealing against a layer of carbon. A good hard ride before and after practise may clear the carbon out. Extra clearance will not hurt anything but clearance increase and slight power decrease and with more clearance more ticking. The only worry would be if you continue to ride only at low revs then the carboning may get worse. Good Luck!

Correct, carbon on the valve seat increases the clearance. I've never seen a valve seat that bad. The valves would be really leaking with those conditions. I've only seen valves and valve seats that were messed up in other ways and leaking.

edit: just thinking... a mis-firing cylinder would do that. Carbon all over the place. Or one that was drawing oil into the cylinder and trying to burn it.

Edited by ReconRat
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I have not had this a straight parking lot bike long enough to have carbon build up, its only had a few parking lot sessions so far. If it was carbon build up on the exhaust side, why are both exhaust valves out of spec the same amount, and wouldn't I be getting some leakyness, since the carbon would be keeping the valve from seating correctly, thus it would act the same as a partially open valve, I should notice some power loss, ect. I also know the bike is not burning oil.

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Hi, To my knowledge: a slight carbon film on the valve may cause a slight compression leak only noticeable if you were racing or on a dyno or a leak down test. Excessive clearance can only be caused by 3 things: 1. Adjusted that way. 2. Valve stem or cam wear caused by oil starvation or soft components. 3. Carbon build up on valve and seat. Keep riding your bike the same way and check again, if clearance is the same or smaller then it was adjusted that way. If clearance is bigger it would be 2or3. Either way lugging the engine causes carbon build up. Just my opinion and opinions are like a##holes, everyone has one, some stink worse than others. Good Luck

Edited by phugitive
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