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Bearing Technical Information

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Appearance: Bearing surface cracked, areas of lining

Causes: Overloading (lugging engine at low speed under

Cap Shift

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.

Hot Short

Appearance: Bearing surface 

Causes: Breakdown of lubrication

Normal Wear

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

Oil Starvation

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

Accelerated Wear

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

Overlay Fatigue

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)

Dirt Embedment

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

Distorted Crankcase

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)  


AppearanceBearing 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

Dirt on Bearing Back

Appearance: Concentrated area of distress on bearing I.D. with corresponding mark or discontinuity on O.D.

Causes: Foreign particle trapped between bearing back and housing. Damage to bearing back or housing bore (nick, burr, etc.) High spot on bearing back or housing bore due to fretting

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