Exam Question

(a) Crankshaft deflections are measured to detect the misalignment of main bearings. The misalignment occurs due to bearing wear or deflection of crankshaft and also to check the horizontal and vertical alignment of the crankshaft in bedplate, on a direct drive engine the alignment of the bedplate with the tail shaft. Because the hull of a vessel and therefore the engine bedplate move and flex, the alignment of the crankshaft will vary within given limits. It is when the alignment is outside these given limits that the crankshaft is subject to excessive bending stresses which may lead to failure.
(b) The deflection of the crankshaft shall be represented by the value when the engine is cold, and since the values measured when the engine is warm sometimes differ significantly depending on the measured conditions, be minded not to use the value measured when the engine is warm as standard.
Stop the engine and engage the turning gear.
Start measuring deflections from the unit farthest to flywheel