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Crankshaft deflections & wear down gauge readings for marine diesel engine

The diesel engine is a type of internal combustion engine which ignites the fuel by injecting it into hot, high-pressure air in a combustion chamber. In common with all internal combustion engines the diesel engine operates with a fixed sequence of events, which may be achieved either in four strokes or two, a stroke being the travel of the piston between its extreme points. Each stroke is accomplished in half a revolution of the crankshaft.

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Crankshaft Deflections And Wear Down Gauge Readings

In order to prevent crankshaft failure and serious breakdowns, it is absolutely essential to maintain the main bearings of an engine in true alignment. The alignment must be checked as per the maker’s instructions, with the main bearing bridge gauge, and the crankweb deflection gauge. In taking these measurements, extreme care must be taken to see that the journal is bedding on its bearing. The thickness of the lower half main bearing shells must also be measured and recorded. If the reduction in thickness of individual bearing shells is not uniform then the differences will be a true record of misalignment.

A chart is provided by the engine manufacturer that gives the various tolerances which may be allowed. The clock gauge readings taken should be checked against this chart to ascertain that alignment is within satisfactory limits.

Inspections : Cylinder Liner Gauging:

The gaugings of the cylinder liners must also be taken and recorded on the appropriate form. Abnormal wear rate must be investigated and reported to the superintendent. As Cylinder Liners are high cost components, it is important to monitor the specific lube oil consumption and wear rates closely. Other calibrations required by the engine manufacturers must be taken at the appropriate intervals.

Crankcase inspections:

Crankcase inspections must be carried out at, or within, the manufacturers’ running hours. In the case of air starting systems the main air starting line is to be drained and completely vented.
  • Before a crankcase inspection is carried out the turning gear must be engaged, indicator cocks or other cylinder pressure relief devices opened and the air or other starting arrangements must be isolated. In the case of smaller medium speed engines and high speed engines without turning gear the starting arrangements must be isolated, and cylinder pressure relief devices opened. Within the scope of diesel engines from high speed through medium speed to slow speed types, there are a wide variety of arrangements for the running gear and bearings, and all must be examined in accordance with manufacturers’ instructions, however the following checks are to be carried out:
    The running gear such as the crankshaft, main bearings, bottom end bearings, top end bearings, guides, astern bars, etc., must be examined as every opportunity occurs, preferably as soon as the crankcase is safe to enter, after the "finished with engines" order is given.

    In carrying out this examination, attention must be given to the locking arrangements and tightness of all nuts, lubricating oil pipes, piston cooling pipes and glands, if fitted, oil drainage arrangements, drainage lines etc. A sharp look out must also be kept for any sign of white metal flakes or splinters as these are often evident if any bearings have "wiped" or tended to "run".

    Attention must also be given to crankshaft coupling bolts. At three monthly periods the tightness of these nuts must be tested with a light hammer and spanner, care being taken so that the coupling bolts are not unduly stretched. The welding of main bearing girders must be examined for signs of cracking. Maintenance performed on the main engine in the Maintenance Report Form

    The chains and/or gearing driving the camshaft must also be examined. The chains must be kept at the proper tension. It is essential that the crankcase doors are always replaced between overhauling periods when in port to ensure that as little moisture as possible condenses in the crankcase. Care should be exercised to see that ventilators are not directed into the crankcase for the same reason. Crankcase pressure release doors which are fitted to each main engine crankcase should be inspected periodically and the diaphragm, where fitted, renewed if damaged.

    The following instructions regarding the prevention of explosions and fires in crankcases are to be prominently displayed on the engine and all E/Os are to be familiar with them:

    Holding Down Bolts Inspections

    The tightness of holding down bolts, particularly of main and auxiliary engines must be checked every three months. At the time they are examined the chocks should also be tested to ascertain that no movement or fretting has taken place. Special precautions are to be exercised when checking holding down bolts with resilient pads to ensure that the alignment is not distorted. It is also necessary to check these parts if the vessel has been in heavy weather.

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