Top-hat shim

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A top-hat shim (lash cap US) is a small inverted hardened-metal cup placed atop a valve stem. Varying thicknesses of top-hat shims are used to adjust valve clearances in a similar fashion to standard flat disc shims (as used in Fiat SOHC/DOHC, Volvo and early Jaguar engines) where the cam-lobe operates directly on the valve without an intermediate rocker-arm. Top-hat shims offer a dramatic weight reduction over standard disc shims and are used in applications where valve-train weight reduction is important (i.e. high-performance road and race orientated engines).