bearing fail
DESCRIPTION
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BEARINGFAILURE
Return to Index
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SelectiveLeaching
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What is Selective Leaching
The term selective leaching is indicativethat in this type of corrosion one element
of a metal or alloy is singled out forselective corrosive attack.
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How Does Selective Leaching Occur ?
Organic acids are produced when base oil
oxidizes during normal engine operation.
Sulfuric acid formed as a byproduct ofcombustion preferentially attacks Copper athigh temperatures. Similarly, Lead gets
corroded by organic acids which aretransported by oil and affect all copper and
Lead components of engine.
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How Selective Leaching is Prevented?
Alkaline reserves (TBN) and dispersants in oil are used up in
doing their job after an extended period in use. Corrosionresults when the acids produced by oil are no longerneutralized or dispersed by oil additives as the additivepackages gets depleted by continuous use. Hence it is
essential to change oil BEFORE the additive package isdepleted.
To prevent Selective Leaching it is also essential to useLOW SULFUR content fuel as high Sulfur content in fuelmay produce acids containing Sulfur as combustion
byproducts and corrode / damage Copper components.
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Con Rod Bearing Seizure (Contd..)
• Probable Cause
Selective Leaching
Minimum Points to bechecked in Field
a) Pitting on bearings on loaded
portions.
b) Copper exposure in some of thebearings.
c) Check for oil change intervalrecords.
d) Effects / abnormality on otherlead and copper components.
e) Check used oil TBN.
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Spalling
Spalling is a form of Cavitation Corrosion occuring
on the unloaded portion of an insert bearing. This is
visible in the form of erosion
and is normally apparent only in bearing overlaymaterial. This overlay cavitation / spalling is
caused by dynamics of oil film as it moves along
the crank and bearing joint. This condition should
not be confused with other types of corrosion.
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Con Rod Bearing Seizure (Contd..)
• Probable Cause
Spalling
Minimum Points to bechecked in Field
a) This cavitation should be only
on the unloaded portion of the
bearing.b) Generally the cavitation will
have a definite boundary..
c) To confirm it is not chemical
corrosion check used oil TBN,
TAN, water & fuel content.
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Con Rod Bearing Seizure (Contd..)
• Probable Cause
Selective Leaching
Minimum Points to be
checked in Field
a) Shining marks on all con rodand main bearings.
b) Overlay wipage on all Upperbearings.
c) Condition of other Bushingsand Main bearings should besimilar.
d) Low Viscosity of oil.e) Percent of fuel in oil.
f) Sources of oil dilution with fuel.
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Con Rod Bearing Seizure (Contd..)
• Probable Cause
Oil contamination
by Coolant
Minimum Points to be checked inField
a) Most of the bearings will exhibit milky gray
colour edging the copper wear area.
b) Indication of brownish discoloration may bevisible if chromate concentration is poor of
coolant
c) Effects of coolant in oil should be visible on
other lube oil related components.
d) White milky sludge in oil inside tappetcover/breather etc.
e) Check for condition of filter paper.
f) Check for components minutely which can
lead to coolant in oil.
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Con Rod Bearing Seizure (Contd..)
Probable Cause
Improper Parent
Bore Finish
Minimum Points to be checked inField on other Bearings.
a) Steel back bearing will show mirror finish
instead of Hatch mark pattern.
b) Check all parent bore dimensions.
c) The parent bore of failed bearing may be
distorted, hence check bores of balance
con rods / main journals to arrive at
conclusions.