Internal combustion engines experience severe valve train wear and the reduction of valve seat and seat insert wear has been a long-standing issue. In this work, worn valve seats and inserts were examined to obtain a fundamental understanding of the wear mechanisms and the results were applied in developing new valve seat insert materials. The new exhaust valve insert material for gasoline engines is a sintered alloy steel containing Co-base hard particles, with lead infiltrated only for inserts used in unleaded gasoline engines. The new intake valve insert material for gasoline engines is a high-Mo sintered steel, obtained through transient liquid phase sintering and with copper precipitated uniformly. This material can be used for both leaded and unleaded gasoline engines.Valve and valve seat insert wear has long been an issue of concern to engine designers and manufacturers. Although new PM (powder metallurgy) techniques for producing seat inserts have been introduced,1), 2), 3) and 4) their advantages have been outpaced by demands for improved engine performance.5) These demands include higher horsepower, lower fuel/oil consumption, and longer maintenance-free life. The authers have been involved in the development of new maintenance-free engines for years. In developing these engines, it has been necessary to develop new valve seat insert materials.In the process of developing new PM valve seat insert materials, engines under development have first been built and operated with extant valve seat inserts. Investigations were then made of worn valve seats and inserts, and the results obtained were applied in developing new valve seat insert materials.