Engine crankshaft failure problem

1. The fillets at both ends of the crankshaft journal are too small
When grinding the crankshaft, the grinder failed to correctly control the fillet of the crankshaft. In addition to the rough processing of the arc surface, the radius of the fillet was too small, so when the crankshaft was working, a large stress concentration was generated at the fillet, and the crankshaft was shortened. fatigue life.

2. Crankshaft main journal axis offset
The axis deviation of the main journal of the crankshaft 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.

3. The crankshaft’s cooling ratio is too large
After the crankshaft is used for a long time, especially after the accident of burning tiles or smashing the cylinder, it will have a large bend, and it should be removed and corrected by cold pressing. Due to the plastic deformation of the metal inside the crankshaft during calibration, a large additional stress will be generated, thereby reducing the strength of the crankshaft. If the cold stress is too large, the crankshaft may be damaged or cracked. This kind of crankshaft will break soon after installation.

4. The flywheel is loose
If the flywheel bolts are loose, the crankshaft assembly will lose its original dynamic balance, and the diesel engine will vibrate after running. At the same time, a large inertial force will be generated, which will cause the crankshaft to fatigue and easily break at the tail end.

5. Poor quality of the crankshaft itself
Don't be greedy for cheap when buying crankshafts, you must purchase from regular channels. Check carefully before installing, and replace or return the product in time if there is any problem. In addition, when the engine is overhauled, the crankshaft should be inspected by magnetic flaw detection or oil immersion percussion inspection. If there are radial or axial cracks extending to the shoulder fillet on the journal surface, the crankshaft can no longer be used.

6. The main bearing bushes are not in the same axis
When the crankshaft is assembled, if the centerlines of the main bearing bushes on the cylinder block are not in the same axis, the diesel engine will be prone to burnout and shaft-holding accidents after operation, and the crankshaft will also break under the strong action of alternating stress.
Seven, crankshaft assembly clearance is too large
If the gap 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 burn the bush to hold the shaft, and the crankshaft will be easily damaged.

8. 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 burn and work before reaching the top dead center, which will cause the diesel engine to knock and cause the crankshaft to be impacted by alternating stress. If the amount of oil supplied to each cylinder is uneven, the crankshaft journals will be stressed unevenly due to the inconsistency of the explosion of each cylinder, resulting in premature fatigue and cracks.

9. the crankshaft is poorly lubricated
If the oil pump is severely worn, the lubricating oil passage is 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 bush, resulting in dry friction and causing the burning pad to hold the shaft , breaking the crankshaft and other major accidents.

10. The crankshaft breakage occurred before the operation
If the throttle is too large or too small during operation, frequent braking or long-term overload operation, the crankshaft will be damaged due to excessive torque or impact load. In addition, when the diesel engine has accidents such as speeding, cylinder smashing and top valve, the crankshaft is also prone to breakage.

Fault Diagnosis and Elimination of Engine Crankshaft Fracture

In order to prevent the crankshaft from breaking, the following measures can be taken during maintenance:

First of all, before repairing the crankshaft, carefully check whether there is any crack on the crankshaft, pay special attention to the fillet transition part, if there is any crack, the shaft should be scrapped. When polishing the journal, the journal and the crank arm should maintain a certain fillet radius, and the radius of the fillet must not be reduced arbitrarily, and attention should be paid to the surface finish of the fillet, otherwise stress concentration will occur and the crankshaft will break