Appearance: Bearing surface cracked, areas of lining

Causes: Overloading (lugging engine at low speed under

Appearance: Wear or fatigue near bearing parting lines on opposite sides in upper and lower bearing halves

Causes: Mixed bearing caps. Reversed bearing cap. Poor doweling of cap to housing. Use of oversized socket. Housing not machined and assembled at same bolt torque. Mating faces of housing not flat or parallel.

Appearance: Bearing surface 

Causes: Breakdown of lubrication

Appearance: Uniform wear pattern approximately 2/3 of the bearing's surface. Wear should diminish near the parting line ends of the bearing, and the wear pattern should extend uniformly across the bearing in the axial direction

Appearance: Bearing surface streaked and smeared with worst damage at center. Heat discoloration. May show pick-up of bearing material on shaft depending on severity. Note: this condition will pass progress into 'Wiping' and 'Hot Short'.

Causes: Low oil level, blocked oil pick-up oil pump failure, blocked oil hole or oil passage, excessive dilution of oil fuel or coolant, lubrication system not primed before start-up

Appearance: Wall thickens reduced from original dimension. Bearing surface worn and polished but not smeared, torn, or scored. No evidence of heat, no embedded foreign particles

Causes: Poor journal surface finish. Wear in the presence of adequate lubrication to prevent heat build up and wiping of caused by peaks in the journal surface finish profile which penetrate the oil film and abrade the bearing. Always grind opposite to rotation and polish in the direction of rotation

Appearance: Network of fine cracks in surface layer of a Trimetal bearing

Causes: Overloading (lugging engine at low speed under High load, over fueling, detonation). Localized concentration of load due misalignment (edge loading, bent rod, tapered, hourglass or barrel shaped housing or journal)

Appearance: Bearing surface speckled, darkened, and lightly or heavily scratched

Causes: Foreign particle contamination. Engine components not thoroughly cleaned prior to assembly. Wear particles from another engine component. Faulty air filter. Neglected oil filter replacement. Dirt entering engine during oil addition

Appearance: Bearing surface darkened, spongy, etched by chemical attack

Causes: Acids in oil. Excessive operating temperature. Excessive blow by. Coolant contamination of oil. Use of high sulphur fuel. Excessive oil change interval

Appearance: With main bearings arranged as installed in the engine, bearings show a progression of damage from one to another

Causes: Main bearing bores out of alignment. Engine over heating. Improper tightening of engine components (bearing caps, heads, manifolds, etc.) Engine not properly or uniformly supported (large stationary engines)  

Appearance: Bearing surface smeared or scratched and torn. Bearing metal and re-solidified along edges

Causes: lubrication systems not primed before start up. Clogged oil passage. Oil pump failure. Improper installation (oil hole blocked). Concentrated loading in localized area of bearing. Misalignment of shaft and bearing surfaces. Insufficient clearance

Appearance: Bearing back polished from movement in housing. Areas of pock marks or build up due to metal transfer between bearing and housing

Causes: Insufficient crush. Oversize housing. Bearing cap and housing not torque properly. Foreign object between cap and housing faces. Over stressed cap and bolts

Appearance: Bearing surface scratched and torn

Causes: Excessive foreign particle contamination. Poor crankshaft surface finish. Insufficient lubrication