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Problem with left intake valve.

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After checking my valve clearances all but the left inlet were within spec. This valve had no clearance at all. Stock shims are 2.95, so went with a few smaller thinking that one of these must be the right size. The smallest of which was a 2.80 shim. Now that`s a difference of .15mm so you would think that it would be within the spec clearance range of .10 - .15mm, right? This shim created a clearance of only .03mm. The valve was obviously very tight.

I`ve order even smaller shims, but I`m concerned. I read on this board that if the valves move 2 full sizes or .10mm they need to be replaced with new ones and new seats have to be cut. If this is true, what exactly needs to be replaced? Just the inlet valve? Both valves?

Thanks

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Your correct.:) You didn't mention the year of your bike or the last time you checked your valves or did a top end but if that valve moves again(which it should) You should proceed as you mentioned.

Peace!:D

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It`s an 08 KX250F and I checked the valve clearance about a month ago and everything seemed fine. Though I now feel that I must have somehow made a mistake. I initially checked the clearance because I was having trouble starting it and it wouldn`t idle. But at that time I had just rejetted for the hot, humid summer here in Okinawa and I thought that was a likely cause. After several jetting changes I just recently rechecked the valves and found the definitive cause.

Today, as an experiment I used fine grit sand paper to decrease a 2.80 shim down to a 2.75mm. I fit perfectly and against my better judgement and the manual caution, I installed the shim and started the bike. It now starts and idles fine, but sounds `loose` but that may be just because I had gotten used to it sounding `tight`.

I`ll install the proper shim when I get it in a couple of days.

But the question remains: how long is this going to last? If you`re doing the math, that`s a movement of .20mm. Twice the rule of thumb for replacing valves.

In the meantime, I guess I start shopping for valves!

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You didn´t say how many hours on that engine, or how hard it was raced, but maybe you should get some new airfilters and be extra careful in the future with filter service. Valve jobs are expensive!

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D-K,

No more than 43 hrs on the engine and, I`m no pansy, but I`m not always on the gas either.

I use 3 air filters, all of which are in perfect condition and cleaned after every ride no matter what their condition. If there`s one thing I`m anal about it`s filter maintanace.

I`ve read a few theories as to why, but it`s alway the left intake valve while all others are still fine.

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That´s funny, I have 68 hours on my stock valves with no problems...

Well, I guess you can never really know exactly what happens in there all of the time...

After all, these are racing engines and shit happens...

Hope you get it fixed..

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