The rocker arm in the car is actually a two-arm lever that changes the direction of the force coming from the pushrod and acts on the end of the valve rod to push the valve away. The ratio of the length of the two sides of the rocker arm is called the rocker arm ratio, and the rocker arm ratio is about 1.2 to 1.8, of which one end of the long arm is used to push the valve. The working surface of the rocker head is generally cylindrical and can slip along the end face of the valve rod when the rocker arm is swinging, so that the force between the two can act along the valve axis as much as possible. There are also oil passages and oil holes in the rocker arm. In the short arm end threaded hole of the rocker arm, screw in the adjustment screw to adjust the valve clearance, and the head ball of the screw contacts the concave seat at the top of the pushrod.