Class 2 (2nd Engineer) MEP 📅 Jan 2023

Exam Question

In the case of a main propulsion engine explain the indications and possible effects which might be expected from:

(a) Insufficient bearing clearance

(b) Excessive bearing clearance and

State the recommended bearing clearances for the bottom end, top end and main bearings of your last motor vessel.

Reference Answer

(a) Bumping clearance is the distance between the piston top and the cylinder cover when the piston is at the Top Dead Center (TDC). For safe and efficient compressor operation, it is typically maintained at 0.5% to 1% of the cylinder diameter .
1. If Bumping Clearance is Too Small:
The piston may physically strike the cylinder cover, leading to mechanical damage, including deformation of the piston, cylinder head, or connecting rod.
Frequent breakdowns and repairs may occur due to damage caused by insufficient clearance.

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