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The influence of engine oil viscosity on the wear of piston rings and cam faces has been investigated by fired engine tests using a radioisotope (RI) tracer technique. High-temperature and high-shear-rate (HTHS; 150°C, 1O6 s-1) viscosities of the experimental oils prepared are 2.2, 2.4, 2.6 and 3.1 mPa•s. At an oil temperature of 90°C the wear of piston rings and cam faces did not increase, even if the HTHS viscosity was lowered down to 2.2 mPa•s. However, both piston rings and cam faces exhibited an increase in wear below 2.4 mPa•s at 130°C. It was also recognized that valve train wear did not significantly increase with reducing viscosity in the motored engine tests at a temperature of 50°C. From these test results, it was suggested that the oil with the HTHS viscosity of 2.6 mPa•s sufficiently demonstrates the antiwear performance equivalent to that with around 3.0 mPa•s for application to piston rings and cam faces.

A laboratory scale simulation test method was developed to evaluate deterioration of radial lip seals of fluoroelastomer (FKM) compounds for engine crankshafts. The investigation of the collected radial lip seals of FKM compounds from the field with service up to 450,000km indicated that the only symptom of deterioration is a decrease of lip interference. This deterioration was not duplicated under conventional test conditions using an oil seal test machine because sludge build up at the seal lip caused oil leakage. However, revised test conditions make it possible to duplicate the deterioration experienced in the field. An immersion test using a radial lip seal assembled with the mating shaft was newly developed. This test method was found to be useful to evaluate deterioration of radial lip seals using FKM compounds. Oil additives affect the deterioration of lip seal materials significantly. Therefore, immersion tests of four different oils were conducted to evaluate this effect.

This paper deals with the effect of engine oil additives, carbon particles and rocker arm materials on the valve train wear of diesel engines. The tests were performed with an ISUZU 1.8L OHC type diesel engine powered by the motored engine method. The sixteen experimental oil formulations were based on the orthogonal method of experimental design. The results were obtained as follows, (1) It was confirmed there were main effects and interactions between each additive component for the valve train wear with a statistical analysis. (2) The failure phenomena and anti-wear properties of the valve train were affected by the additive components, rocker arm materials and carbon particles. The type of zinc dithiophosphate was a very important factor in the valve train wear.