Effect of Tappet Materials on Pitting in Diesel Engine

Various tappet failure modes occur by high contact stress between cam and tappet. Especially, tappet pitting by fatigue has critical influence on engine endurance.

In this study, tappet pitting in diesel engines is discussed. In case of fatigue-pitting, fatigue crack is initiated parallel to the surface at the subsurface where the shear stress is the maximum. Four kinds of tappets for the induction hardened steel cam are chosen to investigate the effect of subsurface microstructures on the fatigue-pitting. It has been found that both sintered material and tufftrided chilled cast iron show excellent pitting resistance.