Overhead Valve

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An overhead valve (OHV) is a type of 4-stroke engine, also called pushrod engine or I-head engine is a type of piston engine that places the camshaft in the cylinder block (usually beside and slightly above the crankshaft in a straight engine or directly above the crankshaft in the V of a V engine) and uses pushrods or rods to actuate rocker arms above the cylinder head to actuate the valves. Lifters or tappets reside in the engine block between the camshaft and pushrods.

This contrasts with an overhead cam design which places the camshaft(s) above the cylinder head and drives the valves directly or through short rocker arms. In an OHC engine, the camshaft(s) are normally part of the cylinder head assembly, while in an I-head engine the camshaft (rarely more than one) is part of the main engine block assembly.