valvetrain

A valvetrain or valve train is a mechanical system that controls the operation of the intake and exhaust valves in an internal combustion engine. The intake valves control the flow of air/fuel mixture (or air alone for direct-injected engines) into the combustion chamber, while the exhaust valves control the flow of spent exhaust gasses out of the combustion chamber once combustion is completed. Layout The valvetrain layout is largely dependent on the location of the camshaft. The common valvetrain configurations for piston engines - in order from oldest to newest - are: Flathead engine: The camshaft and the valves are located in the engine block below the combustion chamber. Overhead valve engine: The camshaft remains in the block, however the valves are located in the cylinder head above the combustion chamber. Overhead camshaft engine: The valves and camshaft(s) are in the cylinder head above the combustion chamber. Components The valvetrain consists of all the components responsible for transferring the rotational movement of the camshaft into the opening and closing of the intake and exhaust valves. Typical components are listed below in order from the crankshaft to the valves. Camshaft The timing and lift profile of the valve opening events are controlled by the camshaft(s), through use of a carefully shaped lobe on a rotating shaft. The camshaft is driven by the crankshaft and— in the case of a four-stroke engine— rotates at half the speed of the crankshaft.