Examination of Wear Mechanisms in Automotive Camshafts

S. Jahanmir, “Examination of Wear Mechanisms in Automotive Camshafts,” Wear, 108 (1986) 235-254.

Two worn camshafts from a taxi fleet test were examined by scanning electron microscopy, energy-dispersive analysis by X-rays, Auger emission spectroscopy and secondary ion mass spectrometry. The cam lobes were selected to represent the extremes of cam wear. The two different lubricant formulations used in the engines differed in the VI improver, the dispersant, the antioxidant and the antiwear additive. This investigation showed that surface deformation and fatigue are the primary wear mechanisms on the cam lobe surfaces in the absence of catastrophic wear by scuffing. The fatigue pits were larger and more numerous on the cam lobe with the larger amount of wear. It was also found that lubricant additive components penetrate along the microcracks and the graphite flakes to a great depth. It is suggested that the penetrated lubricant components may cause accelerated fatigue crack growth by stress corrosion cracking.

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