CRF's Only Forums

Hi guys, new to the forum so hello everyone.

I have an 05 250R and a couple of weeks ago my bike started running bad...anything over half throttle (or when trying to rev higher in the rev range) the bike would splutter and misfire. Anyway I won't go into the details of everything I tried to eliminate the possibilities (new spark plugs/coil/jets/timing), I thought I'd check the valve clearances just to make sure (even though I'd checked them about 3 weeks ago) and one of the exhaust valve shims is missing! Has anyone come across this before, how would it disappear?! The clearance on that particular valve was on the tighter side of the tolerance so it's not like it had enough space to slide out. I'm now thinking I'll have to strip the engine to find the shim unless it appears in the oil when i drain it. On a KTM I had a couple of years ago there was a magnetic bolt that attracted any bits of metal, CRF's don't have anything like that do they? Cheers for your help guys, I'm praying it's going to be in the oil somewhere and I know I'm lucky it didn't get caught in the cam chain but will still be pissed off if I gotta strip the engine!

welcome to CRF's Only! the exhaust shims sit up kind of high. if you adjusted them and didn't get it full seated or had the clearance incorrect it's possible this is how it escaped. under normal clearance and conditions the shim would not be able to escape. as you mentioned, you do need to recover it. that shim could do some serious damage. check down in the left crankcase cover. use a magnetic pickup tool to try and retrieve it. otherwise pull the cover. check on the fly wheel as it may end up attached there.

we offer magnetic oil covers:

http://www.crfsonly.com/catalog/product ... ts_id/2828

again, welcome!

ken

Just a question Ken. Are the shims stainless steel ?
I would have thought that they would be.

Hi Ken, thanks for the help it's much appreciated. I'd like to think I know how to check/adjust clearances properly but clearly something is amiss as one has escaped! I'll pull the crank cover and hopefully it'll be in there - I have a magnetic tool too so finding it shouldn't be too hard. Thanks for the link on the magnetic covers I'll have a look at those.

The shim is not stainless and will attach to a magnet, i used a magnetic tool to remove the exhaust shims when i re-shimmed
Do not start or rotate your engine before you find the shim! If it jams it will do some serious damage!

Back2-2 wrote:Just a question Ken. Are the shims stainless steel ?
I would have thought that they would be.

if they have a minimum of 10.5% chromium they would be considered stainless steel. they are magnetic which means they likely only have enough chromium to keep them from rusting under normal conditions. it's nickel in some stainless steel alloys which make them non-magnetic. so, the magnet test does not eliminate a metal from being stainless steel.

The only way u can really loose that sihim would be if the valve stuck open. And u had enough clearance for it to fall out I would check the valve guides first. U might be pulling the head any way.

Hopefully u figure it out.

Definitely pull the left side engine cover to retrieve the shim. You may want to inspect the exhaust valve rocker for damage as well as the cam. Look at the decompressor mechanism. I hope you find the shim and can get it back together without any hassles or $$.