Class 2 (2nd Engineer) MEKM 📅 Dec 2018

Exam Question

With Respect to Large two-stroke crosshead Main Engines:

(a) Sketch and describe a crosshead designed to prevent or minimize bearing edge loading.

(b) State how the arrangement described achieves its purpose.

(c) What would be an acceptable range of bearing clearance for the top end bearing and bottom end bearings of a large two-stroke marine diesel engine.

Reference Answer

(a) Design of a crosshead in a large two-stroke marine diesel engine:
The pin diameter is made larger to distribute the load over a greater surface area, reducing the load per unit area on the bearing. This also increases the relative sliding speed between the pin and the bearing, aiding lubrication.
The bearing shells are lined with layers of materials designed for specific purposes:
Flash Layer (2-5 µm): 100% tin to prevent oxidation and act as a dry lubricant during initial operation.

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