Exam Question
(a) What is the importance of measuring bearing clearance in a diesel engine (4)
(b) What is Bridge gauge? Describe it's usage withs diagram (6)
(c) What are the other recommended methods used onboard in check bearing clearances (6)
Class 4 (4th Engineer)
MEKM
📅 Sep 2024
Reference Answer
### (a) Importance of Measuring Bearing Clearance (4 Marks)
The measurement of bearing clearance is a critical diagnostic and preventative maintenance task for any diesel engine. The clearance is the small space between the rotating journal (of the crankshaft) and the stationary bearing shell, which is filled with lubricating oil. Its importance stems from the following fundamental principles:
1. **Formation of Hydrodynamic Lubricating Film:** The primary function of bearing clearance is to allow for the formation of a hydrodynamic oil wedge. As the journal rotates, it pulls oil into the wedge-shaped clearance space, generating a high-pressure film that physically separates the moving surfaces. This oil film supports the load and prevents metal-to-metal contact.
* **Too Little Clearance:** Restricts oil flow, preventing the formation of a stable film. This leads to boundary lubrication, increased friction, overheating, and eventual wiping or seizure of the bearing.
The measurement of bearing clearance is a critical diagnostic and preventative maintenance task for any diesel engine. The clearance is the small space between the rotating journal (of the crankshaft) and the stationary bearing shell, which is filled with lubricating oil. Its importance stems from the following fundamental principles:
1. **Formation of Hydrodynamic Lubricating Film:** The primary function of bearing clearance is to allow for the formation of a hydrodynamic oil wedge. As the journal rotates, it pulls oil into the wedge-shaped clearance space, generating a high-pressure film that physically separates the moving surfaces. This oil film supports the load and prevents metal-to-metal contact.
* **Too Little Clearance:** Restricts oil flow, preventing the formation of a stable film. This leads to boundary lubrication, increased friction, overheating, and eventual wiping or seizure of the bearing.
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