WITH the advent of light motor-oils, S.A.E. 10-W and S.A.E. 20-W and the introduction of copper-lead bearings in passenger-car and motor-truck engines, new lubrication-factors have arisen with respect to motor-oil stability as well as with respect to the nature of compounds used for the breaking-in period.
This paper describes a series of tests which were run using S.A.E. No. 11 babbitt bearings and lead-copper and leaded bronze bearings. The relative extreme-pressure characteristics of the various motor-oils, both mineral and compounded, were recorded. In addition, the coefficients of friction were plotted as ordinates (ƒ) and the viscosity, angular speed and pressure (ZN/P) as abscissas were correlated. For this phase of the work, test apparatus had to be developed.
The effect of the mineral and compounded motor-oils on the bearing metals and the causes of deterioration, and vice versa, and the effect of the bearing metals on the stability of the motor oils were checked.
The summation of the data shows that certain metals cause some mineral oils to deteriorate more readily than others and that high acidity in motor-oils causes not only more rapid decomposition of the lubricants themselves but of the bearing metals as well. The coefficient of friction varies with the different metals and with the different combinations of compounds.