Crankshaft Breakage Failure
Signs: A muffled knocking sound occurs in the crankcase, which intensifies with increased throttle. The engine vibrates severely at idle, and black smoke is emitted from the exhaust. Crankshaft breakage is caused by mechanical fatigue at the crankshaft journal shoulder, and there is a gradual process from crack to breakage. In cases of latent cracking, the signs are not obvious; as the crack expands, the signs become increasingly apparent, eventually leading to crankshaft breakage and engine shutdown. If the engine stops when the throttle is adjusted or the knocking frequency matches, it may be at the critical point of crankshaft breakage. At this point, remove the cover for inspection. Manually push the flywheel; if the axial clearance is large and pushing is not difficult, it indicates that the crankshaft has broken.
Treatment Measures: Stop the engine immediately upon discovering the signs and inspect. If cracks are found, replace the crankshaft promptly.