overhead valve

Short definition from Wiktionary

Noun

1. 1
   A type of valve in an internal combustion engine, and thus also (metonymic) the type of valvetrain design, the type of engine that uses it, or an instance of such an engine; this design has the inlet and exhaust valves in the cylinder head (and therefore above the piston). The camshaft can be beside the pistons (with pushrods and rockers operating the valves) or above the valves, with the latter u