What is "cam-in-block"

The cam-in-block valvetrain layout of piston engines is one where the camshaft is placed within 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. This contrasts with an overhead camshaft (OHC) design which places the camshafts within the cylinder head and drives the valves directly or through short rocker arms.

Placing the camshaft inside the engine block has a long history in its use in valve-in-block engines, in straight and V configurations, the Ford flathead being exemplary of the type. Pushrod overhead valve engines with the cam in the block were long used in Chevrolet and Buick straight engines from the 1930s through the mid-1950s and in various similar six-cylinder engines until the extensive employment of the V6 configuration in the 1980s.

There are three main cam-in-block designs:

• L-head, also known as L-block, flathead or sidevalve
• F-head
• I-head, also known as overhead valve (OHV)