Abstract: In the working process of a large wheeled tractor engine, the oil nozzle jammed phenomenon was found. After dismantled the oil nozzle, some metal fragment was found inside. By comparing the microstructure of fragment and the related parts in fuel injector assembly, it was found that the microstructure of fragment was consistent with the microstructure of high-pressure oil pipe in fuel injector assembly. After cut the high-pressure oil pipe longitudinally, some metal burrs formed during machining were found in pipe joints. It was showed that the fragment caused oil nozzle failure was from metal burrs in high-pressure oil pipe.