Composition and classification of engine valve train

The valve mechanism of a four-stroke engine generally consists of a valve group and a valve transmission group. According to the arrangement of camshafts on the engine, the common valve train can be divided into two categories: overhead camshaft and lower camshaft (including middle camshaft). Generally, toothed belt or chain drive is adopted. The advantages of toothed belt are no lubrication, low working noise and slightly worse service life than chain. Compared with toothed belt, the disadvantage of chain drive is that it needs lubrication and the transmission noise is high. Its advantages are reliability and long service life as the engine.