Coated Valve Train Components and Low Emission Engine Oils in a Fired Engine Enviroment

A series of heavy-duty diesel, fired engine tests were run using coated valve train components in combination with low emission diesel engine crankcase oils. Examination of coated rocker arm and corresponding, uncoated crosshead surfaces, showed that greater crosshead wear was encountered using a physical vapor deposition (PVD) chromium nitride coating, as compared with that observed using a tungsten carbide PVD composition, or an uncoated rocker arm surface. Good coating adhesion was observed with both coatings, with no adverse effects on neighboring, uncoated surfaces. Tungsten carbide in combination with the first of two low-emission engine oils out performed either of the oils used in combination with chromium nitride. Test parameters are summarized along with key engine data obtained. Observations from surface characterization of representative rocker arm and mating crosshead components, using optical and scanning electron microscopy coupled with energy dispersive spectrometry also are highlighted and discussed.