Exam Question
(a) Describe the reasons for checking crank web deflections. (8)
(b) Describe the procedure for taking and recording crank web deflections of main engine. (8)
Class 4 (4th Engineer)
MEP
📅 Jul 2023
Reference Answer
### (a) Reasons for Checking Crank Web Deflections (8 Marks)
Crank web deflection measurement is a critical diagnostic procedure for assessing the alignment of a large, slow-speed diesel engine's crankshaft. Misalignment, if left uncorrected, can lead to excessive bearing wear, fatigue failure of the crankshaft, and ultimately catastrophic engine failure. The primary reasons for this check are as follows:
1. **To Assess Main Bearing Wear:** This is the most fundamental reason. The crankshaft is supported by a series of main bearings. As a bearing wears down, its corresponding journal sinks lower than the adjacent ones. This forces the webs of the crankthrow on either side of the worn bearing to be pinched together at the top and spread apart at the bottom. The deflection gauge measures this web distortion, providing a direct indication of bearing wear and misalignment.
2. **To Monitor Hull and Bedplate Deformation:** A ship's hull is not a rigid structure. It flexes and deforms due to:
Crank web deflection measurement is a critical diagnostic procedure for assessing the alignment of a large, slow-speed diesel engine's crankshaft. Misalignment, if left uncorrected, can lead to excessive bearing wear, fatigue failure of the crankshaft, and ultimately catastrophic engine failure. The primary reasons for this check are as follows:
1. **To Assess Main Bearing Wear:** This is the most fundamental reason. The crankshaft is supported by a series of main bearings. As a bearing wears down, its corresponding journal sinks lower than the adjacent ones. This forces the webs of the crankthrow on either side of the worn bearing to be pinched together at the top and spread apart at the bottom. The deflection gauge measures this web distortion, providing a direct indication of bearing wear and misalignment.
2. **To Monitor Hull and Bedplate Deformation:** A ship's hull is not a rigid structure. It flexes and deforms due to:
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