1989-09-01

An Overhead Cam Wear and Valvetrain Dynamics Study 892149

A 22 hour engine test was developed to evaluate the effects of fuels, lubricants, and valvetrain dynamics on the wear of OHC 2.3L engine camshafts and finger followers. Procedures include a break-in to improve test repeatability and a test sequence to allow single-shift operation. A surface analyzer capable of measuring cam lobe wear profiles to micro-inch accuracy provided a quantitative wear comparison.A pure mineral oil, as expected, resulted in higher camshaft wear than using a fully formulated SF lubricant. Cam and follower wear increased significantly when ethanol replaced gasoline as fuel. The combination of ethanol, mineral oil and heavy duty valve springs was selected to increase test severity for hardware discrimination.The average wear of the intake lobes was greater than the exhausts. Kinematic analysis and visual inspection of the valve train mechanism revealed differences in the relative motion and contact stress pattern. Insufficient hydrodynamic oil film, long duration of high contact stress and entrapment of abrasive particles appear to cause increased wear. Methods to reduce cam wear are suggested.

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