Reuse Valve Shims?

[RRoller123]

Looking for a definitive study, or paper, etc. on whether valve shims can be reused safely. I have read (don't remember where.. it was a long while ago) that the shims get slightly concave cupped, they take on the profile of their matched cam lobe, and each cam lobe rides at a slightly different location on the shim, with a slightly different wear profile, and that if you reuse them they may not rotate properly in the cup, and the mismatched profile could cause quick wear on the cam lobe, and if you put them in upside down to try and get around this, they may not seat properly in the cup..(taking a breath)....

So I am curious if anyone knows if there is any definitive study on this, a paper or tech article or anything that addresses the question? Measuring clearances today, will very likely have to adjust every single valve due to the complete block rebuild, flycut short block, and the use of a very small amount of hi-temp RTV sealant on the cam box gaskets, which likely added a thou or two to the height..

Thanks,

Pete

[Odoyle]

Have never had any of my shims come out concave, usually they are just shiny and flat from the wear, buckets and shims can float freely making me think they would wear mostly even. As for reusing, new shims where you can, reusing old ones not the end of the world, but do require that you confirm thickness with micrometer. Did it on a couple valves I didn't have right clearance for, better to use a used shim in right size then a new shim in wrong size, obviously new shim in correct size is ideal.

[RRoller123]

Yeah, I agree. I only had one turn out to be off, and of course that was the one that I didn't have the correct size for in a new shim. Needed a 4-10. So I reused an old one from the stash.

This is just one of those deeply technical topics that I find really interesting. Going to look through the SAE archives and see if they have anything on it. The crowd on FB says that all the dealers used to re-used them, but I am little skeptical of this, as they would have had a supply of new ones available. Except when they didn't...

Allison 274FI cams, Intake spec 0.010", Exhaust spec 0.010"-0.012". I set the Intakes all to 0.011-0.012" and the Exhausts all to 0.012"-0.013" A little loose is good.

Pete