1. Wear down of main bearings causes misalignment, leading to the bending of the crankshaft. This bending increases operational stresses, particularly during rotation.
2. The centerline of the crankshaft and propeller shaft may form an arc due to uneven wear, leading to improper alignment with other engine components.
3. Worn bearings cause the intermediate crank throws to deflect, resulting in the crank opening at the bottom position and closing at the top. This can compromise the smooth rotation and operation of the crankshaft.
4. Wear reduces journal and bearing surface contact to point contact, increasing localized loads and causing loss of effective lubrication. This can lead to overheating and bearing surface damage.
5. Severe cyclic stresses are induced on the crankshaft's webs, journals, and crankpins, increasing the risk of fatigue failure over time.
6. Misalignment and stress concentrations lead to excessive vibrations, which can propagate through the system, causing mechanical failure in other engine parts.

In conventional built-up crankshafts, the connection between the journals and the webs is a shrink fit, which relies entirely on a frictional grip to prevent relative movement. This type of fit is achieved by making the journal's diameter slightly larger than the hole in the web. The journal is cooled (typically with liquid nitrogen) to shrink it before it is inserted into the web. As it warms up, it expands, creating an extremely tight interference fit that is dependent solely on friction.

This frictional grip is critical because any slippage between the journal and the web can alter the timing of that particular engine unit. Slippage can be caused by various factors, such as:

• A propeller colliding with a submerged object, causing a sudden resistance to rotation.
• A seizure in a running gear component.
• A hydraulic lock during engine start.
• Extreme overloading.

If slippage occurs, it changes the engine's timing. If the slippage exceeds a critical value, often around 5∘, the engine may fail to start and experience uneven loading, which compromises its overall reliability and can lead to a catastrophic failure. Because the entire function and integrity of the crankshaft depend on preventing this slippage, total reliance is placed on the frictional grip of the shrink fit.

Oil holes are drilled in crankpins and journals to supply lubrication to bearings and other moving components. However, if the oil holes were drilled without modification, their sharp edges would create sudden changes in the cross-sectional area. Such abrupt changes act as stress raisers, causing high stress concentration.

A high-stress concentration significantly reduces the fatigue life of the component. The higher the stress, the fewer the number of cycles the material can withstand before a fatigue failure occurs. To counteract this, fillets are added to the oil holes.

A fillet is a smooth, curved transition that provides a gradual change in area. Larger fillets create a smoother transition, which effectively distributes stress and drastically reduces the stress concentration at the opening of the oil hole. By reducing this localized stress, the fatigue life of the crankpin and journal is greatly increased, ensuring the long-term reliability of the component.