Valve overhead
The valve overhead type is the most widely used type of valve train. Both the intake and exhaust valves hang upside down on the cylinder head. Valve group includes valve, valve guide, valve seat, spring seat, valve spring, lock plate and other parts; valve transmission group generally consists of rocker arm, rocker arm shaft, push rod, tappet, camshaft and timing gear. When the working cycle of the cylinder needs to open the valve for ventilation, the crankshaft drives the camshaft to rotate through a transmission mechanism (such as a timing gear), so that the cam protruding part on the camshaft pushes the rocker arm through the tappet, push rod and adjusting screw With a swing, the other end of the rocker arm pushes down on the valve and further compresses the spring. When the apex of the convex portion of the cam turns over the tappet, the thrust to the tappet is gradually reduced, and the valve opening gradually decreases under the action of the spring tension until it is finally closed. During the compression and power strokes, the valve is tightly closed under the action of spring tension.