The Role of Hydroperoxides in Engine Wear and The Effect of Zinc Dialkyldithiophosphates

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Abstract
Value train wear was examined in a motored 2.3 l engine similar to that wed in the Sequence V-D test. A procedure was developed in which model hydroperoxides were added to the crankcase oil to simulate used oil. Cam lobe and follower wear occurred, apparently as a result of direct attack by the hydroperoxides on rubbing surfaces rather than through oil oxidation. The extent of wear was proportional to the hydroperoxide concentration. The same type of hydro-peroxide-induced wear subsequently was identified in a fired bench engine and in a field test. The study also showed that zinc dialkyldithiophosphates (ZnDDP) control wear by decomposing hydroperoxides in addition to modifying surfaces in boundary contact. Secondary ZnDDPs' were more effective than primary ZnDDPs'.