Preventing valve train wear in automotive engines i s one of the most importantproperties of anengine oil. However, the influence of engine oil additives on valve train wear has not been suffliently clarifld. In this investigation, the antiwearperformance of additives (such as ashless dispersants, metallic detergents and zinc dithiophosphate -WTP) and the influence of the interaction of the additives were evaluated. Firstly, ashless dispersants (such as succinimides. succinic esters and benzylamine-type additives) did not appear to provide signfxant antiwear protection in valve train wear tests. However, a succinimidecontaining boron demonstrated excellent antiwear performance.Secondly, metallic detergents were considered. An overbased calcium sulphonate and an overbased phenate were found to have good anti-scufmg performance when evaluated in engine tests and in Falex wear tests. However,from the results of four-ball tests, these additives did not appear to have many extreme pressure properties. From surface analyses, it was determined that a calcium carbonatefrlm was formed on the sliding surface of the Falex test piece, and thisfrlmprovidedgood protection against wear.Finally, the interaction of m T P , succinimides and calcium detergents and their influence on valve train wear were studied. The decornosition temperature of ZDTP increased with certain additives, including the succinimide. As a result, scufmg was more prone, at temperatures below those increased temperatures. Also, changes in additive concentration on the sliding surface. due to competitive adsorption, altered the antiwear performance of the oa

The shiftability of manual transmissions is known to be strongly affected by the nature of the transmission oil. When conventional sulphur—phosphorus (SP) additives are used in the oil, gear clashing, sticking, and other problems occur. As reported previously, these problems are caused mainly by the polysulphide used in the SP additives. This paper reports on a study of the effect of the structure of the polysulphide's hydrocarbon chain on the synchromesh characteristics. It is found that polysulphides with long hydrocarbon chains have high kinematic friction coefficients and low static friction coefficients. It is also shown that this phenomenon occurs because of the adsorption of the polysulphide on to the copper alloy of which the gear synchroniser ring is made. By using a polysulphide with a long hydrocarbon chain it is possible to develop transmission oils that have superior load‐carrying capacity and better shiftability even when compared with the latest transmission oils that contain metallic detergents.

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