As internal combustion engines began to develop separately to steam engines, poppet valves became increasingly common.īeginning with the 1885 Daimler Reitwagen, several cars and motorcycles used inlet valve(s) located in the cylinder head, however these valves were vacuum-actuated ("atmospheric") rather than driven by a camshaft as with typical OHV engines. This was the case for the first Otto engine, which was first successfully run in 1876. The first internal combustion engines were based on steam engines and therefore used slide valves. History 1894 prototype overhead valve Diesel engine 1904 patent for Buick overhead valve engine Predecessors Some early intake-over-exhaust engines used a hybrid design combining elements of both side-valves and overhead valves. 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 therefore are strictly speaking overhead valve designs. 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. This contrasts with earlier flathead engines, where the valves were located below the combustion chamber in the engine block.Īlthough 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. Type of piston engine valvetrain design Components of a traditional OHV engine valvetrainĪn overhead valve (OHV) engine, sometimes called a pushrod engine, is a piston engine whose valves are located in the cylinder head above the combustion chamber.
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