Failure mode of rocker arm support bearings.

Scuffing

Some support bearings of rocker arms sequentially show severe wear damage indicated by scuffing. Oil analysis where performed to determine the condition of the engine oil. The oil analysis report gave a lack of anti scuff (EP) additives. In order to prevent this type of damage oil analysis when used as part of a routine program might be effective.

EP additives typically adhere onto the metal surface by adsorbing either by physical or chemical attraction. Where asperities come into contact under boundary lubrication conditions, high (flash) temperatures in the micro contacts initiate the additives to form a protective layer by chemical reaction with the metal surface.

Historically, EP additives were made with lead soaps, active sulphur and later chlorinated compounds. By the mid-1950s, lead soaps were eliminated from additive packages and replaced with zinc and phosphorus additives. Organic zinc compounds are found in larger amounts in oils specifically blended for racing applications. In order to protect catalytic converters the percentage of zinc content in modern engine oils is minimal. Proper oil analysis is important be sure the specified amount of additive is present and to monitor the condition of the active agent in use.