A scuffing test for piston ring/bore combinations:: Pt. II. Formulated motor lubrication

In the experiments reported in this paper the bench test developed in the first part of this work [J. Galligan, A.A. Torrance, G. Liraut, A scuffing test for piston ring/bore combinations: Pt. I. Stearic acid lubrication, in preparation.] was used to study the time to failure of ring/bore contacts lubricated with a fully formulated motor oil. It was found that failure times correlated well with load, frequency, test temperature and quantity of oil, but that the effect of surface finish, though present, was more difficult to quantify. The main findings in this respect were that there is an optimum finish for long life, and that liner surfaces which are initially highly polished have lives which are more dispersed than those with standard finishes. The rise in friction, which precedes failure, is associated with smoothing of the liner surface to a high polish. The roughening which occurs when scuffing is fully developed is therefore a consequence of the rise in friction rather than its cause.