An 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. This contrasts with flathead engines, where the valves were located below the combustion chamber in the engine block.
1894 prototype overhead valve Diesel engine
1904 patent for Buick overhead valve engine
V8 engine (with intake manifold removed), showing the camshaft, pushrods, and rockers
A flathead engine, also known as a sidevalve engine or valve-in-block engine, is an internal combustion engine with its poppet valves contained within the engine block, instead of in the cylinder head, as in an overhead valve engine.
A crossflow T-head sidevalve engine
1915 Cadillac flathead engine block
Harley-Davidson flathead
BMW R12