Causes of Engine Crankshaft Fracture

First, the rounded corners of the crankshaft journal are too small. When grinding the crankshaft, the grinder fails to properly control the shaft fillet of the crankshaft. In addition to the rough machining of the arc surface, the radius of the fillet is too small, so that the crankshaft works with a large stress concentration at the rounded corner and shorten the fatigue life of the crankshaft. Second, the crankshaft spindle neck axis offset. The axis of the crankshaft spindle is offset, which destroys the dynamic balance of the crankshaft assembly. When the diesel engine runs at high speed, it generates a strong inertial force, which causes the crankshaft to break. Third, the crankshaft's cold comparison is too large. Long-term use of the crankshaft, especially after the occurrence of burning or smashing, will cause large bending, so it should be removed for cold pressure correction. Since the plastic deformation of the metal inside the crankshaft during calibration will generate a large additional stress, thereby reducing the strength of the crankshaft. If the cold gauge is too large, the crankshaft may be damaged or cracked. This crankshaft will soon be broken after installation. Fourth, the flywheel is loose. If the flywheel bolt is loose, the crankshaft assembly loses its original dynamic balance. When the diesel engine is running, it will shake, and at the same time, it will generate a large inertia force, which will cause the crankshaft to fatigue and easily break at the tail end. Fifth, the crankshaft itself is of poor quality. Do not seek cheap when buying a crankshaft, you must buy it from regular channels. It should be carefully checked before installation, and if there is any problem, it will be replaced or returned in time. In addition, when the engine is overhauled, the crankshaft should be subjected to magnetic flaw detection or oil immersion inspection. If the journal surface has radial cracks or extension to the axial crack of the shoulder fillet, the crankshaft can no longer be used. Sixth, different axes of the main spindle bush. When the crankshaft is assembled, if the center line of each main spindle bush on the cylinder is different, the diesel engine is prone to burn accident after the diesel engine is working, and the crankshaft will also break under the strong influence of the alternating stress. Seventh, the crankshaft assembly clearance is too large. If the clearance between the crankshaft journal and the spindle bush is too large, the crankshaft will impact the spindle after the diesel engine is running, but the alloy will fall off and the shaft will be hung, and the crankshaft will be easily damaged. Eighth, the oil supply time is too early or the oil volume of each cylinder is uneven. If the oil supply time of the fuel injection pump is too early, the piston will not burn to the top dead center and will cause the diesel engine to knock and cause the crankshaft to be subjected to the alternating stress. If the oil supply amount of each cylinder is not uniform, the crankshafts will be unevenly stressed due to the inconsistency of the explosions of the cylinders, and the tires will be fatigued and cracked prematurely. Ninth, poor crankshaft  lubrication.

If the oil pump is seriously worn, the lubricating oil channel is dirty and the circulation is not smooth, so the oil supply will be insufficient and the oil pressure will drop, resulting in the formation of a normal lubricating oil film between the crankshaft and the spindle bush, thus causing dry friction, the burning of the shaft, and breaking the crankshaft and other major accidents. Tenth, improper operation causes crankshaft fracture If the throttle is too large or too small, the brakes are frequent or the engine is overloaded for a long time, the crankshaft will be damaged by excessive torque or impact load. In addition, when a diesel engine has an accident such as a flying car, a smashing cylinder, and a top valve, it is also easy to break the crankshaft.