The fractures on the failed valve are around the impact loading area of valve face to valve seat. Fatigue striations and beach marks on the fracture surfaces do not appear. Valve fatigue is not cause of failure.
The crack as seen in valve Ref: picture DSCO 4944 page 2 crack is due to mechanical stress cause from impact loading. Excessive impact loading can be due valve face to valve seat contact area configurations, excessive engine RPM, valve overloading due to abnormal combustion, impact loading exceeding valve material.
