Class 2 (2nd Engineer) MEP 📅 Nov 2022

Exam Question

A completely new unit comprising piston, rings, liners, cylinder head and valves was fitted to a six-cylinder single-acting four-stroke diesel generator. Before installing the clearance and sizes were checked and considered satisfactory. During a trial run the running characteristics were abnormal so the generator was stopped. On examination it was seen that the new piston had badly scored and drubbed the liner and had indication of seizure in the upper part of the liner. Give your reasoned comments for this failure

Reference Answer

The failure of the new piston and liner in the diesel generator can be attributed to a combination of factors, likely stemming from a lack of proper running-in procedures and potentially compounded by issues with lubrication or fuel injection.
Insufficient Lubrication:
The most probable cause of this failure is insufficient lubrication between the piston and the liner. If the lubrication is inadequate, excessive friction can occur, leading to the breakdown of the lubricating oil film. This loss of lubrication results in direct metal-to-metal contact between the piston and liner, causing overheating. The overheating, in turn, can lead to microscopic welding of the piston rings and the liner surface, further exacerbating the friction and eventually leading to seizure. Ensuring that proper lubrication is in place after major overhauls or when new parts are fitted is important. Any fault in the lubrication system, such as blocked oil passages or incorrect oil viscosity, can quickly lead to damage.
Issues with Fuel Injection:

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