The function of the rocker arm is to change the direction of the force from the push rod or cam, and act on the rear of the valve stem to push the valve open. The rocker arm is actually a double arm lever. The ratio of arm length on both sides of the rocker arm (called the rocker arm ratio) is 1.2-1.8. Among them, one end of the long arm contacts with the valve to push the valve, so as to obtain a larger valve lift, and reduce the displacement of the push rod or tappet, thus reducing the inertia force generated by their reciprocating motion.