Common Causes of Crankshaft Fracture

Crankshaft fracture typically begins at the smallest crack, most often occurring at the radius of the connecting rod journal on the head or tail cylinder, where it connects to the crank arm. During operation, the crack gradually expands, eventually breaking suddenly when it reaches a certain size. When inspecting the fracture surface, brown areas are often observed, indicating older cracks, while shiny, glossy structures are the telltale signs of the subsequent sudden break.

1. Engine Crankshaft Fracture Problems

The radius of the crankshaft journals is too small.

During crankshaft grinding, the grinder failed to properly control the radius of the crankshaft's axial corners. In addition to the rough surface finish, the radius of the corners was also too small. This resulted in significant stress concentration at the corners during operation, shortening the crankshaft's fatigue life.

2. Crankshaft Main Journal Axis Misalignment

Crankshaft main journal axis misalignment disrupts the dynamic balance of the crankshaft assembly, generating strong inertial forces during high-speed operation of the diesel engine, leading to crankshaft fracture.

3. Excessive cold bending of the crankshaft. After extended use, especially after bearing burnout or cylinder jamming, the crankshaft will develop significant bending and should be removed for cold straightening. This correction involves plastic deformation of the crankshaft's internal metal, which generates significant additional stress and reduces its strength. Excessive cold bending can damage or crack the crankshaft, potentially leading to breakage within a short period of use.