The camshaft in English is called Overhead camshaft, or OHC for short. Generally, the camshaft mounting position of the engine has three forms: lower, middle, and overhead. The overhead camshaft is such that the camshaft is placed inside the cylinder head, above the combustion chamber, directly driving the rocker arm and the valve without having to pass a long push rod. Compared with the pusher engine with the same number of valves (ie, the overhead valve structure), there are much fewer components that need to reciprocate in the overhead camshaft structure, thus greatly simplifying the gas distribution structure and significantly reducing the weight of the engine. It also improves transmission efficiency and reduces operating noise. Although the overhead camshaft complicates the structure of the engine, it delivers superior engine performance (especially a significant increase in ride comfort) and a more compact engine structure that allows engine manufacturers to quickly become widely used in their products. This design. The driving method of the overhead camshaft and the overhead valve structure is not necessarily different. Power can be transmitted to the overhead camshaft through timing belts, chains and even gear sets.