Uncover Ten Reasons For Engine Crankshaft Fracture

The fracture of the crankshaft usually starts from the smallest crack, and most of the cracks occur at the connecting rod journal fillet of the head cylinder or end cylinder and the connecting part of the crank arm. During operation, the crack gradually expands and suddenly breaks when it reaches a certain level. When observing the fracture surface, it is often found that the brown part is obviously an old crack, and the shiny tissue is the trace that developed to a sudden fracture later. Today, let's take a look at the reason why the crankshaft is broken!

1、 The rounded corners at both ends of the crankshaft journal are too small

When grinding a crankshaft, the grinder fails to properly control the shaft stiffness and fillet of the crankshaft. In addition to rough machining of the arc surface, the radius of the fillet is also too small, resulting in greater stress concentration at the fillet during crankshaft operation, and reducing the fatigue life of the crankshaft.

2、 Offset of crankshaft main journal axis

The deviation of the crankshaft main journal axis destroys the dynamic balance of the crankshaft assembly, and when the diesel engine operates at high speed, it generates strong inertial forces, leading to crankshaft fracture.

3、 Excessive cold play of the crankshaft

After long-term use of the crankshaft, especially after the occurrence of tile burning or cylinder ramming accidents, significant bending may occur, and it should be removed for cold pressure correction. Due to the large additional stress generated by the plastic deformation of the metal inside the crankshaft during calibration, the strength of the crankshaft is reduced. If the cold competition is too large, it may be caused by damage or cracks to the crankshaft, which will break soon after installation and use.

4、 Loose flywheel

If the flywheel bolts become loose, the crankshaft assembly loses its original dynamic balance, and the diesel engine shakes after operation, generating significant inertial forces, causing crankshaft fatigue and prone to fracture at the tail end.

5、 Poor quality of crankshaft itself

Purchase crankshaft should not be greedy for cheap, must be purchased from regular channels. Before installation, it should also be carefully inspected, and if there are any problems, they should be replaced or returned in a timely manner. In addition, during engine overhaul, the crankshaft should be subjected to magnetic flaw detection or oil immersion knocking inspection. If there are radial or axial cracks extending to the shoulder fillet on the journal surface, the crankshaft cannot be reused.

6、 Different shafts of main bearing shells

During crankshaft assembly, if the center lines of the main bearings on the cylinder block are different from each other, the diesel engine is prone to burn the bearings and seize the shafts after operation, and the crankshaft can also fracture under the strong action of alternating stress.

7、 Excessive crankshaft assembly clearance

If the clearance between the crankshaft journal and the bearing bush is too large, the crankshaft will impact the bearing bush after the diesel engine is running, but the alloy will fall off and the bush will burn and hold the shaft, and the crankshaft is also vulnerable to damage.

8、 The oil supply time is too early or the oil quantity of each cylinder is uneven

If the fuel injection pump supplies oil too early and the piston burns before it reaches the top dead center, it can cause knock in the diesel engine and cause the crankshaft to be impacted by alternating stress. If the oil supply quantity of each cylinder is not uniform, the stress on each journal of the crankshaft will be uneven due to the inconsistent explosion rate of each cylinder, resulting in premature fatigue and cracks.

9、 Poor lubrication of crankshaft

If the oil pump is severely worn, the lubricating oil passages are dirty, and the flow is not smooth, the oil supply will be insufficient, and the oil pressure will drop, resulting in the failure to form a normal lubricating oil film between the crankshaft and the bearing shells, resulting in dry friction and major accidents such as burning the bearings, seizing the shafts, and breaking the crankshaft.

10、 Failure to operate has resulted in crankshaft fracture

If the oil valve is too large or too small during operation, frequent braking, or prolonged overload operation, the crankshaft will be damaged by excessive torque or impact load. In addition, diesel engine accidents such as speeding, cylinder ramming, and valve jacking are also prone to crankshaft fracture.