There are three types of camshaft positions: lower, middle and upper. The camshaft of the lower-mounted valve mechanism is located in the crankcase, the camshaft of the middle-mounted valve mechanism is located on the upper part of the body, and the camshaft of the upper-mounted valve mechanism is located on the cylinder head.
Most production cars now have engines with overhead camshafts. The main advantages of the overhead camshaft structure are that there are few moving parts, the transmission chain is short, and the rigidity of the whole mechanism is large, which makes the camshaft closer to the valve and reduces the bottom camshaft caused by the larger distance between the camshaft and the valve. Waste of round-trip kinetic energy. The engine with the overhead camshaft has a higher speed due to the rapid valve opening and closing action, and the running stability is also better.