The effect of three dry lubricants on automotive valve train wear resistance was studied experimentally. Scuffing wear occurs as the cam slides across the lifter face where the rotating motion of the camshaft is converted into the linear motion necessary to drive the cylinder head valves. This scuffing is caused by localized microscopic bonding between the skidding surfaces. It can be minimized by using dry film lubricant coatings to increase the boundary lubrication depth adjacent to the contact area. To compare valve train wear resistance in the laboratory, rotating cam lobes coated with dry lubricants--parkerization, spray-applied graphite coating, and brush-applied molybdenum disulfide coating-were pressed against valve lifters that were constrained in a fixture. The brush-applied molybdenum disulfide coating was the most effective of the three tested lubricants in reducing scuffing wear.
E. Benstead, J. Foyos, M. Smith and O. Es-Said, “Effectiveness of Various Dry Film Lubricant Coatings in Resisting Wear of an Automotive Camshaft to Lifter Interface,” J. of Communications in Reliability, Maintainability, and Supportability, Vol. 3(1), 1996, pp. 31-36.