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4 stroke valve shims being pounded out in the middle?

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I just shimmed my valves and my exhausts were reading a staggering .52mm!!!! they should be .30... so there is .20mm of slack somewhere, and thats a lot. (at least theyre not tight!)

maybe thats what the ticking in my engine is?

anyways.. I took out the old shims and found why they were reading so loose. its not from the valves.

its the shims... the middle of the shims have been pounded down from the valves. where the valve contacts the shim, there is a "crater" in the middle of the shim that is about .2mm deep.

what is causing this?

the shims were 2.45mm.. but they are ruined now, and the part where the valve touches it not 2.45mm thick.. instead it is about 2.25mm thick!!

would I be fine if I put a new 2.50mm shim in there and got rid of the ruined 2.45s? I believe that would get my clearances back to around .28mm

and one final question... is it wise to re-use shims? now that I look closer.. the middles of the used shims where the valve contacts is are all a little bit "beat up". some you can see it starting to wear, some you can barely feel with your finger nail, and some you can see from across the shop. could I just flip them around and put the nice side on the bottom where the valve contacts it or what?

I have the full hot cam shim kit.. but kinda sucks if you can re-use the old shims due to the centers of them being pounded down.

any advice would be greatly appreciated!!! its been a while since I opened the engine, about a year. so I am a little hazy on some things

thanks

ps: the head is a 2008 head from bigborethumpers with approx 60 engine hours on it, trail/forestry. no racing/track. SS intake valves. oil changes every 3-5 engine hours, etc.. all the good stuff.

if it wasnt for the centers of the shims being pounded down by the valves I believe that my clearances would be still almost 100% after 60 engine hours... not bad at all.

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