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.
Inspections : Cylinder Liner Gauging:
- The gauging 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.
- 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 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:
- Sump drain grids for blockage, metal, or other impurities.
- If appropriate to the engine type a lubricating oil pressure test is to be carried out.
- The adequacy of the flow of oil from the bearings, its direction and pattern are to be carefully observed and compared with the manufacturers’ instructions. This test can provide positive indications towards locating faulty bearings.
- Take feeler clearances according to manufacturers’ instructions.
- As appropriate to the engine type and to “built-up” crankshafts the proof marks should be examined for correct alignment. The relevant Management Office must be informed if there is any doubt concerning proof marks.
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 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