Due to the effects of transient load, curvature, speed and surface micro-topography, the marine cam-tappet pair usually works in harsh mixed lubrication state. In this paper, considering the effect of surface roughness, based on the three-dimensional (3D) line-contact mixed EHL model, the transient lubrication state of cam-tappet pair is analyzed. Results show the presence of three-dimensional surface roughness will affect fluctuations in film thickness and pressure clearly, while excessive roughness also cause local stress concentration, the asperity contact and zero film thickness. The lubrication effects of different machined surface methods are compared, and it found that the smallest film thickness ratio occurs as the ground surfaces contact, and lubrication state is very harsh, however, the polished surface can significantly improve lubrication state of the cam-tappet pair. Under low-speed conditions, the contact area ratio is greatly increased, which may cause serious stress concentration and excessive wear. By optimizing the base circle radius, the load-bearing capacity of cam-tapper pair improves clearly and the lubrication state is improved.
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