Rocker Arms

The rocker arms transfer a displacement from the camshaft to the valves. The camshaft has lobes that contact push rods and move them up and down in a periodic manner. The other end of the push rods contact the rocker arms. The arms have a central shaft about which they rotate and an upward motion of the push rod is translated into a downward motion of the valve contacting the other end of the rocker arm. The valve is kept closed by a valve spring until the rocker arm motion opens it against the spring tension.