The valve train consists of the valves and a mechanism that opens and closes them. The opening and closing system is called a cam shaft . The cam shaft has lobes on it that move the valves up and down, as shown in Figure 5 . Click on image to see animation Figure 5. The cam shaft.
Most modern engines have what are called overhead cams .
This means that the cam shaft is located above the valves, as you see in Figure 5. The cams on the shaft activate the valves directly or through a very short linkage. Older engines used a cam shaft located in the sump near the crankshaft. Rods linked the cam below to valve lifters above the valves. This approach has more moving parts and also causes more lag between the cam's activation of the valve and the valve's subsequent motion.