Exam Question
With reference to medium speed trunk piston engines:
(a) explain the purpose of an anti-polishing ring. (5)
(b) Describe how effective piston cooling is provided. (5)
(c) where is the thrust bearing fitted and why? (6)
Class 4 (4th Engineer)
MEKM
📅 Dec 2025
Reference Answer
### (a) The Purpose of an Anti-Polishing Ring (5 Marks)
The primary purpose of an anti-polishing ring, also known as a fire ring or cylinder liner honing ring, is to prevent the phenomenon of 'bore polishing' or 'cylinder glazing' in the upper part of the cylinder liner.
**Mechanism and Function:**
* **Location:** It is a precisely machined cast iron ring fitted into a recess at the very top of the cylinder liner, positioned just above the upper limit of the top piston ring's travel at Top Dead Centre (TDC).
The primary purpose of an anti-polishing ring, also known as a fire ring or cylinder liner honing ring, is to prevent the phenomenon of 'bore polishing' or 'cylinder glazing' in the upper part of the cylinder liner.
**Mechanism and Function:**
* **Location:** It is a precisely machined cast iron ring fitted into a recess at the very top of the cylinder liner, positioned just above the upper limit of the top piston ring's travel at Top Dead Centre (TDC).
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