Several modifications have been made by design engineers to an existing engine platform to increase power output thus creating higher cylinder pressures, flow, and operating temperatures. The engine is rated above 350 hp at a moderate engine speed of 2000 rpm with a cylinder pressure of 2400 psi. The changes create excessive intake and exhaust component wear with often inconsistent exhaust insert wear.
Traditional Silchrome XB (W90) insert material coupled with Sil 1 intake valve material often experiences moderately high wear, but never exceeds the wear objective until the recent modifications. The insert surface wear exhibited a typical pitting type wear pattern related to valve rotation. The surface shows horizontal grooves related to valve rotation with small pockets of removed material. Silchrome XB martensitic steel utilizes chromium, nickel, and silicon to provide oxidation resistance and chromium carbides to resist wear. Typical hot hardness values summarized indicate the limited capability of materials that rely mostly on chromium carbides for wear resistance. The wear is solved by simply using an M2 tool steel (W70V) that utilizes more wear resistant molybdenum and tungsten carbides to improve wear. Notably, a 75 percent reduction in wear results with no change in valve material as the average recession wear is reduced from 0.35 to 0.07 mm in a 1000 hour dynamometer test.
The principal problem created by the modification of this Class 8 diesel engine is inconsistent wear using a nickel exhaust insert material coupled with a cobalt-base common trade material that is faced as the valve material. Nickel-base materials used in diesel exhaust insert applications contain high carbon to form wear resistant carbides with large percentages of chromium, tungsten, or molybdenum. The heavily worn surface shows a severe wear pattern related to shear stress. The change from acceptable to excessive wear is attributed to the increase in temperature that causes an increase in valve flexing and consequently more sliding wear. The Winsert W77T6-P® material is used to solve the problem and reduce recession wear by 66 percent from 0.09 to 0.03 mm in a 1000 hour dynamometer test series. The unique blend and distribution of different carbide types creates a stronger material to resist sliding wear at moderate to high engine speed, and it forms a beneficial oxide film to reduce friction. The Compressive Yield Strength data shows increased base material strength to resist deformation under sliding pressure. W77T6-P® also conducts heat faster than the nickel material to lower the operating temperature of the insert.