Failure Analysis On Heavy Duty Diesel Engine Valve

To meet the particular China local application demands and emission requirement, a type of heavy duty diesel engine made several times technical improvement to upgrade the engine's power and fuel economy and reduce the emission. And appeared massive valve failure and resulted in huge amount of warranty claim after the engine launched in market. After 5-year intensive investigation on hundreds of received failure parts and experimental verification, indicating the valve of the heavy duty diesel engine mainly failed in valve seat face abnormal wear recession, head chordal and radial fracture and guttering, which resulted from the excessive combustion pressure which far exceed the strengthen limit of the cylinder head, and caused cylinder head thermal distortion and also caused valve seat insert thermal distortion due to improper seat insert material selection. The distortion of the cylinder head and seat insert caused valve misalignment seating and seat leakage, and finally caused uneven wear and excessive wear at intake side and fracture and guttering at exhaust side. Secondly, the stresses of the valvetrain have been increased significantly after the engine technical improvement, and degraded the system's design margin, leading to an abusive dynamics in valvetrain system when engine run, and resulting in hard seating when valve closing event which will shapely increase the valve seating stress at the valve head and stem blend, finally cause valve fracture and accelerate the valve seat wear.After the intensive investigation of the valves failure, the root causes of the valve failure have been found and verified. OEM improved the engine design and adjusted engine calibration accordingly, the failure and warranty claim of valve have significantly declined.