Fatigue

Appearance: Bearing
surface cracked, areas of lining
Causes:
Overloading (lugging engine at low speed under
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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.
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Hot Short

Appearance: Bearing
surface
Causes:
Breakdown of lubrication
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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
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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
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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
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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)
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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
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Corrosion

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
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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)
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Wiped

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
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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
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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
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Scoring

Appearance: Bearing
surface scratched and torn
Causes:
Excessive foreign particle contamination. Poor crankshaft
surface finish. Insufficient lubrication
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