Failure analysis of six-cylinder passenger car engine camshaft

The camshafts are responsible for controlling the timing of the intake and exhaust valves at the right time in internal combustion engines. In this study, failure analysis was performed on two camshafts in a six-cylinder car made of gray cast iron. One camshaft failure occurred after about 177,000 kilometers and the other after about 208,000 kilometers between cam 1 and 2. In order to investigate the cause of cam failure, first, a series of tests including determination of chemical composition, microstructure, hardness measurement, and fractography were performed. The morphology of the fracture surface showed that the growth of intergranular crack was from the zone of stress concentration and accompanied by ratchet marks. The hardness measurement results of the camshaft cross-section measured a maximum of 155 HB, while the average surface hardness values of the heat-treated surfaces are suggested to be at least 480 HB. The results of the investigation showed that the phenomenon of crack initiation and eventual failure of the cam can be caused by factors such as excessive load, low hardness, and the presence of impurities in the stress concentration zone of the camshaft.