Under the transmission of the timing belt or timing chain, the camshaft drives the valve to open and close at the correct time, and complete the four processes of intake, compression, work and exhaust with the piston; because the timing belt and timing chain will jump at medium and high speed operation, and the timing belt will elongate, deformation and skip teeth in long-term use because of the material and force of the belt, resulting in inaccurate valve timing, resulting in vehicle fuel costs, weakness, knock and other failures;
when the skip tooth too much because the valve opened too early or closed too late will also cause the valve and the upward piston collision damage to the engine. In order to make the timing belt and timing chain to maintain a suitable tightening degree, that is, not due to too loose and skip teeth and not due to too tight damage, there is a special tightening system, consisting of a tightening device and a tightening wheel or guide rail; the tensioner provides pressure pointing to the belt or chain, the tensioner pulley is in direct contact with the timing belt, and the guide rail is directly in contact with the timing chain, and they apply the pressure provided by the tensioner to it while running with the belt or chain, so that they maintain the appropriate tightening degree.
