* Fatigue: This is arguably the most common cause. Repeated cyclical stressing during engine operation gradually weakens the crankshaft material over time. Tiny cracks develop and propagate, eventually leading to a catastrophic failure. Factors that accelerate fatigue include:
* High engine loads: Consistent operation under heavy load, especially at high RPM, significantly increases stress on the crankshaft.
* Vibration: Excessive vibration, especially unbalanced or misaligned components, can promote fatigue.
* Material defects: Imperfections in the crankshaft's casting or forging can act as stress concentrators, leading to premature failure.
* Improper heat treatment: Incorrect heat treatment during manufacturing can compromise the crankshaft's strength and fatigue resistance.
* Torsional stress: This is twisting stress caused by the reciprocating motion of the pistons. High torque demands, especially sudden increases in load, can exceed the crankshaft's torsional strength.
* Over-torquing: Over-tightening of the crankshaft's main bearings or other connected components can induce stress concentrations and lead to cracking.
* Lack of lubrication: Insufficient lubrication leads to increased friction and wear, causing excessive heat and potentially damaging the crankshaft's bearings and journals. This can lead to bending or breakage.
* External damage: Impacts, collisions, or even improper handling can cause damage to the crankshaft, potentially leading to fractures.
* Bearing failure: If a crankshaft bearing fails, it can allow the crankshaft to move excessively, leading to bending or breakage.
* Resonance: In some cases, the crankshaft can be subjected to resonant frequencies from the engine operation, causing amplified vibrations and potentially leading to failure.
* Improper maintenance: Neglecting regular maintenance, including oil changes and inspections, can significantly increase the risk of crankshaft failure.
In summary, crankshaft breakage is usually a complex issue involving the interaction of multiple factors over time. Understanding these factors is crucial for preventing these failures through proper design, manufacturing, operation, and maintenance.
