Valve Spring Installed Height Variation

You never want to have thin shims [ 010 - 0.015" ] in direct contact with the spring. They can get chewed up. If you have a shim 'package', say a 040 & a 010 together, put the 010 under the 040 & all good. Alum heads use a cup or locator for the springs. Put the shim under these. The shims will not be damaged, even if thin.