Cranckcase Inspection of a Marine Engine
How to inspect a marine main engine crankcase
1) Inform bridge before opening the crankcase door of the main engine.
2) Get confirmation for propeller clearance.
3) Close the starting air to the main engine.
4) Put the board on starting lever to not start the engine.
5) Drain the starting air line.
6) Stop the lubricating oil pump.
7) Open the indicator cocks.
8) Engage the turning gear.
9) Open the crankcase doors.
10) Wear proper protective equipment like shoes, helmet and safety goggles.
11) Carry a small hammer and a torch.
Inspecting the crankcase:
1) Check for any white metal deposits under the bearing.
2) Check all the nuts and bolts if they are properly tightened.
3) Conduct hammer tests for checking bolt tightness.
4) Check the bedplates for any cracks.
5) Check the crosshead bearing guides and shoes for the big engines.
6) Check the axial movement of the connecting rod.
7) Check the ends of all bearings for any worn out white metal.
8) Check the filters in the crankcase.
9) Check for any leakages in the water side of the liner.
10) Gears will be checked for any weardown, corrosion or pitting.
11) After completion of checking, come out of the engine and start the lubricating oil pump.
12) Turn the engine with the turning bar or motor and check the lube oil flow of all bearings.
13) Check the quality of lube oil.
Effects of worn bearings:
1) Lubricating oil pressure will drop.
2) The bearing load capacity will reduce.
3) The compression pressure will drop.
4) The combustion will be improper.
5) The total produced power will reduce.
6) The fuel oil consumption will increase.
7) There will be fatigue in the bottom end bearing bolts which may cause failure.
8) Bearing metal will crack because of the jumping of pin.
The crankcase inspection is of extreme importance to avoid a crankcase explosion. An overheated part in the crankcase called as “hot spot” can cause a crankcase explosion. The lubricating oil coming in contact with the hotspot gets evaporated. This evaporated oil circulates to the cooler parts of the crankcase and condenses to form a white mist. If this mist comeing in contact with the right amount of air circulates back to the hotspot, it will be ignited leading to a primary explosion. This explosion may cause the crankcase doors to blow off and the vacuum created after the explosion will draw atmospheric air into the crankcase where it will combine with the burning oil to cause a bigger secondary explosion.