Valve Problems with Lead Free Gasoline

Use of lead free gasoline results in severe exhaust valve recession in light duty engines. Recession proceeds 10-20 times faster than with leaded fuel, and occurs on the integral cylinder head seats. A wear model is proposed which identifies parameters contributing to recession. Engine tests showed valve seat angle and cylinder head seat hardness and/or structure to be most significant in reducing seat wear. Coatings, wider seats, and improved valve train stability all show plus effects but were insufficient by themselves to stabilize wear rates. Wide seats, use of seat inserts, and lower seat angles resulted in shortened valve burning life in engines run with leaded gasoline. Induction hardened cylinder head seats reduced wear with no effect on valve durability.