Abstract: Aiming at the problem of knocking noise in a turbo-charged engine under development during cold star after a long time out of service, based on the noise and vibration signals of engine in starting process, wavelet transform and angular domain analysis are adopted to identify the cause of knocking noise being the slapping of limiting clasp against the housing of hydraulic tensioner. The slapping mechanism of tensioner is systematically studied from the aspects of dynamic characteristics of lubrication system and valve timing system and sealing, based on which a scheme to increase the spring stiffness in tensioner for completely solving the abnormal noise problem of engine during start after a long time out of service

Key words: valve timing chain system, slapping, hydraulic tensioner