Overhead valve engine

An overhead valve engine, abbreviated (OHV) and sometimes called a pushrod engine, is a piston engine whose valves are located in the cylinder head above the combustion chamber. This contrasts with flathead (or "sidevalve") engines, where the valves were located below the combustion chamber in the engine block.

Although an overhead camshaft (OHC) engine also has overhead valves, the common usage of the term "overhead valve engine" is limited to engines where the camshaft is located in the engine block. In these traditional OHV engines, the motion of the camshaft is transferred using pushrods (hence the term "pushrod engine") and rocker arms to operate the valves at the top of the engine. However, some designs have the camshaft in the cylinder head but still sit below or alongside the valves (the Ford CVH and Opel CIH are good examples), so they can essentially be considered overhead valve designs.

Some early intake-over-exhaust engines used a hybrid design combining elements of both side-valves and overhead valves.^[1]