This is determined by the working principle of the four-stroke engine.The crankshaft rotates 2 revolutions, so one working cycle of the engine is 2 revolutions.

　　However, the valve only needs to be opened and closed within one working cycle, so for the camshaft, the camshaft rotates one revolution in one working cycle of the engine.The advantage of gear transmission is that the transmission accuracy and reliability are good, but the noise is relatively large.

　　The advantages of chain transmission are low transmission resistance and high reliability, but it is also noisy and requires lubrication.The advantages of the toothed belt drive are low noise and no need for lubrication, but the service life is slightly worse. Generally, it is required to be replaced for 30000 kilometers.

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