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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
 ShortAppearance:
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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