Wear of valve train components is one of the most critical factors limiting the life of automotive engines and in the performance evaluation of lubricants. Finger and rocker follower systems, which are commonly used in modern OHC gasoline engines, are particularly wear-prone, the wear profiles of the cam and follower surfaces exhibiting features that have hitherto defied satisfactory explanation.A new mathematical model based on simple wear theory is presented which is shown to be capable of predicting the essential features of the wear profiles of engine cams and followers. The magnitude of the predicted wear is of the correct order and the influence of changing cam/follower clearance and of hydraulic adjustment are consistent with observations of wear in service. The effects of lubricant viscosity and operating speed on the distribution of wear are discussed.The model is also applied to a conventional cam/tappet OHC valve train system. Comparison of these results with those for the pivoted follower systems sheds light upon the reasons for the apparently higher wear observed in the latter type of valve train.