Failure Analysis of an Engine Valve

Some engine valve fractured and the failure reason was analyzed by macro observation, scanning electron microscope analysis, energy spectrum analysis, metallographic examination and hardness test to the valve and rocker arm contacted with the valve. The results show that the manufacture deviation existing in oilhole of the rocker arm resulted in the bad lubrication between the friction pairs of valve and the rocker arm, and made them produced serious abrasive wear. Wear increased the gap between the friction pairs gradually, and then increased the seated force, which induced the stress concentration at the valve neck and production of cracks. The cracks gradually extended and finally resulted in the fracture of the valve.