After completion of regular planned maintenance on one of the main engines, the cylinder covers were mounted back. However, the cover of cylinder number one was not mounted correctly and the guide pin of the cover was not in the recess of the cylinder head on the exhaust side (see image top left).
The misaligned mounted cover resulted in a small 3mm gap between cover and the sealing surface (see image bottom left). This was not noticed at that time by the crew executing the regular maintenance as the gap is not visible from the walk platform side (cam-side).
The next day the main engines where started for departure and the regular checks were done, but the gap was not noticed.
What went wrong
The gap was not noticed because the vessel had a slight list to starboard so the leaked oil was flowing from the cylinder head on the block in between the turbo charger and the regulator into the fuel oil leak tray (see image top right). Only after the vessel made a turn to portside, did the duty engineer notice the oil leak (see image bottom right).
Investigation into the source of the leaked oil led to the discovery of the wrongly mounted cover. Quick action by losing the cover and giving it a gentle tap to make it fall back in its correct position, stopped the oil leakage. The remaining spilled oil was quickly removed from the cylinder head and block. The oil underneath the exhaust gas line was already starting to vaporize so quick removal of this oil was essential to prevent a possible fire.
After the clean-up, one of the engineers was assigned as a fire watch to check the exhaust gas line and engine.
The potential consequences of the oil leakage could have been an engine room fire.
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