In a long time before, bottom type camshaft in internal combustion engine is most common. Usually this engine, the valve is located in the top of the engine, the so-called OHV engine (OverHeadValve, overhead valve). At this point the camshaft is located in the side of the crankcase, usually through distribution agencies (e.g., tappet, push rod, rocker arm, etc.) to control the valve. Therefore stove bottom camshaft also called offset type camshaft in general. Because the valve in the engine camshaft distance far away, and usually only two each cylinder valve, so speed usually slower, comfort, and the output power is low. But the structure of the engine output torque and low speed performance is good, the structure is simple, easy to maintenance. Now most of the car number of engine is equipped with overhead camshaft. Overhead camshaft type structure makes the camshaft is more close to the valve, reducing the stove bottom camshaft due to the large distance between the camshaft and valve between kinetic energy waste. Overhead type camshaft engine because the valve opening and closing action more quickly, higher speed, smooth degree of the movement of the better. Earlier appeared overhead type engine camshaft structures are SOHC (SingleOverHeadCam, single overhead camshaft) engine. The engine was installed at the top only a camshaft, so generally each cylinder only two or three valve (one or two at the inlet and exhaust a), limited by the high speed performance. And technology to update some is DOHC type (DoubleOverHeadCam, overhead camshaft) engine, the engine because is equipped with two camshafts, each cylinder can be installed four to five valve (two) intake from two to three, exhaust, high-speed performance has been significantly promoted, but meanwhile, low-speed performance will be affected by certain effect, the structure becomes complicated, difficult to repair.