Found a sequence IVA paper, which lead down a rabbit hole http://www.astmtmc.cmu.edu/ftp/docs/gas/...dure_draft4.pdf http://papers.sae.org/940794/
We were able to identify engine blow-by as a primary factor affecting camshaft wear in gasoline engines. Using a 2.3-liter overhead-camshaft engine, we isolated the valve-train oil from the crankcase oil and its blow-by using a separated oil sump. We find that: with engine blow-by, the camshaft wear was high. without blow-by, the camshaft wear was low. with blow-by piped into the isolated camshaft sump, the wear was high again.Later studies identified nitric acid as a primary cause of camshaft wear. It is derived from nitrogen oxides reacting with water in the blow-by. But even in the presence of blow-by, camshaft wear can be controlled by the proper selection of zinc dithiophosphates (ZnDTP) and detergent type.
An analysis was made of wear factors by investigating the effect of engine operating conditions on valve train wear. It was found that cam nose wear increased as larger amounts of combustion products, including nitrogen oxides and unburned gasoline, became intermixed with the engine oil. Based on these results, a valve train wear test procedure has been developed for evaluating cam nose and rocker arm wear under engine firing conditions.It has been confirmed that this test procedure correlates will with ASTM Sequence VE test and CCMC TU-3 test.
A study of seasonal effects on a low temperature Valve Train Wear (VTW) test has been carried out with the Nissan KA24E engine test. Initial tests in our laboratory with this engine with an in-house reference oil showed that VTW was more severe in the hot and humid Japanese summer compared to the very dry winter. This prompted a systematic study of VTW performance using a temperature and humidity controlled cell, this being carried out with a JASO reference oil and an in-house reference oil. This work clearly showed that cam nose height loss correlated linearly with absolute humidity, higher wear being measured under higher humidity conditions. The slope of this relationship varied with the lubricant, presumably reflecting the differing sensitivities of lubricant formulations to humidity-induced wear. A relationship was also found between VTW and sulphate ion content of used oils. Overall, this study highlights the need to control ambient temperature and humidity for a low temperature VTW test.
Continued interest in energy conservation and carbon dioxide emissions has resulted in enhanced opportunities for development of fuel efficient lubricants. This fuel efficiency has been achieved to a large extent by reducing viscosity as far as volatility and lubrication requirements allow. There has been much industry activity to assess fuel efficient lubricants without compromising engine durability. One area of potential durability concern is that of the overhead camshaft (OHC) rocker follower configuration widely used in modern passenger car engines. A motored cylinder head from an industry standard wear test having an OHC rocker follower configuration has been instrumented to measure oil film thickness (OFT) in an exhaust valve contact by means of an electrical capacitance technique. OFT measurements over the whole of the active part of the cam cycle are presented using both single and multigrade oils based on a variety of commercially available viscosity index improvers at an operating temperature of 100°C. Using single grade oils the measured OFT over the cam nose region was only slightly dependent on the lubricant viscosity for all test conditions. Under steady state motored conditions metallic asperity contact was absent and the surfaces were separated by an electrically insulating film which was present at all times. These observations would suggest that the dominant contribution to measured OFT is due not to viscosity but to the presence of anti-wear films on the metallic surfaces. The effect of adding VIIs to single grade base oils is to enhance the OFT in the predominantly elastohydrodynamic lubrication regimes in the cam flank regions of the cam cycle. However, little OFT enhancement could be found in the heavily loaded regions outside the cam flank regions when using multigrade oils. There is evidence that at higher camshaft speeds the measured film is composed of a surface film augmented by a small hydrodynamic contribution, however it would appear that the surface films laid down under lower speed conditions are more tenacious than those deposited under thicker film operation. Observed wear maxima on the cam follower surface occurred as predicted at positions associated with extended durations of contact with the cam. An apparent thinning of the film occurs (below that observed with single grade oils) when using lower viscosity multigrade oils, around the same positions in the contact cycle.