13ht Jun. 05

Auxiliary Engine of MAN Make built at Ranchi (India) with 5 cylinders and 650 KW power was running without any trouble. Suddenly load tripped off and stopped. On investigation we found one of the unit connecting-rod bolts slackened and piston/liner damaged (Shored heavily).

Liner/ Piston/ Conrod and con-rod bolts were renewed. After normal checkup only visually, engine was restarted.

Within a few minutes of starting found RPM dropping; so engine was stopped, manually to investigate further. Once again found the same unit con-rod bolt slack and slight damage to the Liner/ Piston.

A thorough investigation was then carried out with the help of shore associates but cause was not conclusively pin pointed though the unit was kept was ready after reconditioning Liner/Piston.

While doing liner pulling some water had fallen into the crankcase and so decided to do crankcase cleaning and renewed the oil. One worker brought a threaded plug to me saying that he found the same in the crankcase.

Immediately I started investigating on this new tack.

Since the piston is oil-cooled and the oil flow is through the radial holes drilled in the con rod and the crank shaft, main heavy oil supply is also connected to the last web of the crank shaft, which is plugged on the other side.

The concerned unit plug had gotten slackened and fallen into the crankcase. This has caused no oil flow to the piston and since the piston is Aluminum Alloy, due to the heat it expanded, leading to seizure.

Lesson: During C/Case inspection special attention should be given to the plug tightening. It is better to tighten the plug fully in and spoil the outer thread, so that the plug does not come out.

Also during C/case inspection ensure piston cooling oil flow positively by Hand Pump or priming up.
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