MAIN ENGINE PISTON CROWN GETTING HOLED :
Main Engine Type : MITSUBISHI 8 UEC, OIL COOLED, 3 EXHAUST VALVES POPPET TYPE
The incident took place while passing Bay of Biscay. Sea condition was very rough. Around 1100 hrs it was observed that the engine rpm was fluctuating and also LO pressure found fluctuating. The engine was stopped, and the engine was turned with indicator cocks open. Found the LO coming out from one of the indicator cocks. Inspection was carried out through the scavenge ports, it was found that the piton top was holed for that particular unit. LO pump was stopped and the engine was allowed to cool.
Since the weather was very rough and hence the piston could not be replaced with the o’hauled one. It was decided to isolate the unit and the piston LO inlet passage was blanked. This was done as follows: The palm bolts were slackened by taking the piston to BDC. Then the piston was taken to TDC, and wooden supports for the piston were arranged thro’ scavenge ports. After allowing the piston to rest on top of the wooden supports, the copper blank was placed and the palm nuts were tightened. LO pump was started and the leakages were checked and rectified. Engine was started and the ship proceeded on the voyage at reduced speed. When the weather became calm, engine was again stopped and the piston was replaced with a spare one.
The removed piston was further checked thoroughly and found that the piston crown had burnt out very badly beyond the limits. It seemed that during the earlier overhaul, this burn out was not measured or checked.
It is advisable to have the piston crown gauged at every o’haul to avoid such mishaps out at sea.