VALVE AND VALVE MECHANISMS
There are two
valves for each cylinder in most enginesone intake and one exhaust. Since these
valves operate at different times, it is necessary that a separate operating mechanism be
provided for each valve. Valves are held closed by heavy springs and by compression in the
combustion chamber. The purpose of the valve actuating mechanism is to overcome spring
pressure and open the valve at the proper time. The valve actuating mechanism includes the
engine camshaft, the camshaft followers (tappets), the pushrods, and the rocker arms.