Influence of Low Lead Fuels on Exhaust Valve Performance

An extensive series of tests has been completed to evaluate accelerated exhaust valve seat wear which occurs in passenger car engines with lead-free gasoline. Results indicate that the predominate factor contributing to seat recession is vibration induced relative motion between the valve and seat. Engine speed rather than load or temperature showed the greatest influence on accelerated wear. Various combinations of valve head shape including changes in seat angle, seat width, and valve head stiffness were studied. Fixed versus rotated valves, various valve materials, and face coatings and fuel additive evaluations also were made. Reduced valve seat angles and hardened seats showed the greatest reduction in valve seat wear with lead-free gasoline.