Exam Question
(a) Describe using sketches a top end bearing arrangement designed to minimise or prevent the risk of oil film overload. (10)
(b) Explain why successful lubrication of top end bearings is difficult to achieve in practice. (6)
Class 4 (4th Engineer)
MEKM
📅 Dec 2022
Reference Answer
### (a) Top End Bearing Arrangement to Prevent Oil Film Overload
A top end (or crosshead) bearing in a large two-stroke marine diesel engine is designed to withstand extremely high, uni-directional firing pressures while operating under conditions of low-speed oscillating motion. To prevent the breakdown of the lubricating oil film and subsequent overload, modern designs incorporate several specialized features.
#### 1. Concept of Operation
The primary challenge is to create and maintain a hydrodynamic oil film in the absence of continuous rotation. This is achieved by forcing high-pressure lubricating oil into precisely machined grooves and wedges in the bearing's bottom half, which bears the combustion load. The design aims to mechanically generate the oil wedge that cannot be formed naturally by rotation.
A top end (or crosshead) bearing in a large two-stroke marine diesel engine is designed to withstand extremely high, uni-directional firing pressures while operating under conditions of low-speed oscillating motion. To prevent the breakdown of the lubricating oil film and subsequent overload, modern designs incorporate several specialized features.
#### 1. Concept of Operation
The primary challenge is to create and maintain a hydrodynamic oil film in the absence of continuous rotation. This is achieved by forcing high-pressure lubricating oil into precisely machined grooves and wedges in the bearing's bottom half, which bears the combustion load. The design aims to mechanically generate the oil wedge that cannot be formed naturally by rotation.
Full answer on MeoMock — surveyor-grade reference answers for 7,000+ written exam questions.
Prepare on Android — MeoMock on Google Play