bearing fail

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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.