Insufficient bearing clearance:

Indications:

• Increase in bearing temperature due to reduced oil flow and friction.
• Dark brown appearance of lubricating oil caused by overheating and oxidation.
• High oil mist content indicating excessive wear or overheating.
• Increased amperage of the turning gear motor, highlighting resistance during engine rotation.
• Presence of white metal particles in lubricating oil analysis, indicating bearing material damage.

Effects:

• Excessive heat can cause the bearing's white metal layer to melt or wear away.
• Metal-to-metal contact leads to surface damage (scoring) on the crankpin and bearing surfaces.
• High heat generation may cause the bearing and shaft to seize.
• Overheated oil may cause oxidation and degrade into sludge.
• Overheating and wear can lead to permanent bearing failure.

Excessive bearing clearance:

Indications:

• Noisy operation, often characterized by a knocking sound caused by the clearance between components.
• Drop in lubricating oil pressure due to increased leakage at the bearing clearance.
• Presence of white metal particles in the oil analysis, indicating wear or damage.

Effects:

• Metal-to-metal contact may occur as the hydrodynamic oil film is compromised.
• Over time, the bearing may experience accelerated wear or failure.
• Can lead to irregular engine speed.
• Excessive clearance causes imbalance and increases vibrations in shaft.

Sketch showing lubricating oil passage to crank pin bearing: