What are cylinder head shims?
Shims are thin ‘spacers’ placed between the block and the head. They are used to fine tune the distance between the piston at the top of a stroke and the head. This is done for a number of reasons, including to restore valve train geometry, valve clearance, compression ratio, and cam timing to factory specifications on engines where the cylinder head and/or block surfaces have been resurfaced. The gasket on the other hand is a compressible, fibrous material that is used to achieve a seal between the block and the head. Shim failure can affect the integrity of the seal of the head gasket, which can lead to a loss of compression amongst other things. A way to improve shim design is to ensure that its hardness matches that of the block. This will allow the gasket to compress in the same manner as if it were compressing directly onto the block itself. You don’t want your shims to deform under the compression of the gasket.
