.crankshaft failure

Factors contributing to failure on a crankshaft

Cracks

• Different parts of crankshaft are subjected to different kinds of stresses.
• Cracks weakens crankshaft areas thus leads to failure.

Crankshaft corrosion attack

• Decomposition and oxidation of oil in service
• Contamination of lubrication oil by fuel oil
• Contamination of lube oil by acidic products of combustion (4 stroke engine)
• Possibility of stray electric current entering crankcase resulting electro chemical corrosion
• Oil carrying air bubble with it causes pitting corrosion

Crankshaft twisting or slipping

1. If an attempt is made to start the engine when:
   1. Turning gear is engaged
   1. Water or fuel accumulation on piston crown.
   1. Propeller is confined by ice log
2. During operation propeller strikes with submerged object
3. Seizure of engine component.
4. Bottom end bolts failure.
5. Crash astern movement.

Misalignment of crankshaft

1. Main bearing damaged
2. Defective propeller shaft bearing
3. Slack or broken tie bolts
4. Foundation bolts loosen or fracture
5. Engine chocks broken, cracked, or fretted
6. Bedplate deformed / damaged
7. Hull deformation due to Grounding; Fire
8. Weakening of structure due to corrosion

Checking crankshaft deflection/alignment

.crankshaft deflection .deflection .cd  .csd

We take crankshaft deflection to make sure that the crank runs and maintain proper balance

Preparation 

• Take immobilization permission
• Block starting air valve and put sign
• Propeller clearance
• Tool box meeting
• Risk assessment and work permit done
• Enclosed space entry permit done
• Open crankcase door and ventilate and then check with oxygen analyzer
• Weather is calm
• No operation of loading discharging
• Ship not in drydock
• No maintenance on other engine part

Procedure

Deflections results interpretation

Vertical deflection:

• Difference between top and bottom clearance is the vertical deflection

Horizontal Deflection

• Difference between port and starboard side clearance is the horizontal deflection.
• This value is usually very low.

 Accuracy checking of deflection reading

The values of T+B and P+S should nearly the same. Otherwise, the measurement need to be repeated for the unit.