Exam Question
With respect to medium speed, diesel engines,
(a) Describe types of main bearing failure (8)
(b) Describe prevention of each type of failure (4)
(c) What are the reasons for crankpin bearing bolt failure? (4)
Class 4 (4th Engineer)
MEKM
📅 Feb 2023
Reference Answer
### (a) Types of Main Bearing Failure (8 Marks)
Main bearings in medium-speed diesel engines are precision components operating under severe conditions. Failure can be categorized based on the underlying physical or chemical mechanism:
1. **Fatigue Failure (Cracking/Pitting)**:
* **Mechanism**: Caused by repeated cyclic loading from combustion pressures and rotating/reciprocating masses. This cyclic stress, when exceeding the material's endurance limit, initiates microscopic cracks on the surface or subsurface of the bearing material (lining). These cracks propagate and join, causing pieces of the bearing material to break away, resulting in pitting or flaking.
Main bearings in medium-speed diesel engines are precision components operating under severe conditions. Failure can be categorized based on the underlying physical or chemical mechanism:
1. **Fatigue Failure (Cracking/Pitting)**:
* **Mechanism**: Caused by repeated cyclic loading from combustion pressures and rotating/reciprocating masses. This cyclic stress, when exceeding the material's endurance limit, initiates microscopic cracks on the surface or subsurface of the bearing material (lining). These cracks propagate and join, causing pieces of the bearing material to break away, resulting in pitting or flaking.
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