Visual Inspection of Main Bearings and Connecting Rod Bearings {1202, 1203, 1225, 1230} Caterpillar

Caterpillar Products

All Cat Engines

Introduction

Table 1

Revision	Summary of Changes in SEBF8009
36	Added new serial number prefixes.
35	Republish due to structure issues.
34	Added best practice bearing layout and repaired 2 pixelated illustrations.
33	Added new serial number prefixes.

© 2019 Caterpillar® All Rights Reserved. This guideline is for the use of Cat dealers only. Unauthorized use of this document or the proprietary processes therein without permission may be violation of intellectual property law.

Information contained in this document is considered Caterpillar: Confidential Yellow.

This Reuse and Salvage Guideline contains the necessary information to allow a dealer to establish a parts reusability program. Reuse and salvage information enables Caterpillar dealers and customers to benefit from cost reductions. Every effort has been made to provide the most current information that is known to Caterpillar. Continuing improvement and advancement of product design might have caused changes to your product which are not included in this publication. This Reuse and Salvage Guideline must be used with the latest technical information that is available from Caterpillar.

For technical questions when using this document, work with your Dealer Technical Communicator (TC).

To report suspected errors, inaccuracies, or suggestions regarding the document, submit a form for feedback in the Service Information System (SIS Web) interface.

Canceled Part Numbers and Replaced Part Numbers

This document may not include canceled part numbers and replaced part numbers. Use NPR on SIS for information about canceled part numbers and replaced part numbers. NPR will provide the current part numbers for replaced parts.

Important Safety Information

Illustration 1	g02139237

Work safely. Most accidents that involve product operation, maintenance, and repair are caused by failure to observe basic safety rules or precautions. An accident can often be avoided by recognizing potentially hazardous situations before an accident occurs. A person must be alert to potential hazards. This person should also have the necessary training, skills, and tools to perform these functions properly. Safety precautions and warnings are provided in this instruction and on the product. If these hazard warnings are not heeded, bodily injury or death could occur to you or to other persons. Caterpillar cannot anticipate every possible circumstance that might involve a potential hazard. Therefore, the warnings in this publication and the warnings that are on the product are not all inclusive. If a tool, a procedure, a work method, or operating technique that is not recommended by Caterpillar is used, ensure that it is safe for you and for other people to use. Ensure that the product will not be damaged or the product will not be made unsafe by the operation, lubrication, maintenance, or the repair procedures that are used.

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Improper operation, lubrication, maintenance or repair of this product can be dangerous and could result in injury or death. Do not operate or perform any lubrication, maintenance or repair on this product, until you have read and understood the operation, lubrication, maintenance and repair information.

Safety precautions and warnings are provided in this manual and on the product. If these hazard warnings are not heeded, bodily injury or death could occur to you or to other persons.

The hazards are identified by the safety alert symbol which is followed by a signal word such as danger, warning, or caution. The "WARNING" safety alert symbol is shown below.

Illustration 2	g00008666

This safety alert symbol means:

Pay attention!

Become alert!

Your safety is involved.

The message that appears under the safety alert symbol explains the hazard.

Operations that may cause product damage are identified by "NOTICE" labels on the product and in this publication.

Caterpillar cannot anticipate every possible circumstance that might involve a potential hazard. The safety information in this document and the safety information on the machine are not all inclusive. Determine that the tools, procedures, work methods, and operating techniques are safe. Determine that the operation, lubrication, maintenance, and repair procedures will not damage the machine. Also, you must determine that the operation, lubrication, maintenance, and repair procedures will not make the machine unsafe.

The information, the specifications, and the illustrations that exist in this guideline are based on information which was available at the time of publication. The specifications, torques, pressures, measurements, adjustments, illustrations, and other items can change at any time. These changes can affect the service that is given to the product. Obtain the complete, most current information before you start any job. Caterpillar dealers can supply the most current information.

Summary

This guideline contains information about bearing construction, disassembly, and assembly procedure recommendations of the engine lower structure and how engine parts relate to bearing performance. A visual inspection guideline of bearings is also provided. This guideline does not include reuse information for bearings. Caterpillar recommends bearing replacement at any bearing inspection or when the connecting rod or main cap bolted joint is opened, unless the bearings have less than 200 operational hours. Bearing replacement is recommended due to increased risk of failure at subsequent at reinstallation.

Although not recommended, Caterpillar recognizes customers may choose to reuse bearings. There may be situations where reuse will be a necessity as no spare parts are available. If the customer chooses to reuse bearings, the recommendation is that the running surfaces of bearings being reinstalled do not have damage, such as from debris, abnormal wear, scuff, or smear, fretting (backside), or hot spots.

To make the illustrations more clear, descriptions of possible failures have been included. More information on failure analysis can be found in SEBV0544Applied Failure Analysis, "Engine Bearings".

Service Letters and Technical Information Bulletins

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NOTICE
The most recent Service Letters and Technical Information Bulletins that are related to this component shall be reviewed before beginning work. Often Service Letters and Technical Information Bulletins contain upgrades in repair procedures, parts, and safety information that pertain to the parts or components being repaired.

References

Table 2

References
Media Number	Title
M0080689	Reuse and Salvage Guideline, "Cylinder Block Cleaning and Audit Procedure"
SEBF8042	Reuse and Salvage Guideline, "Reuse and Salvage for Crankshafts"
SEBF9011	Reuse and Salvage Guideline, "Dynamometer Testing of Caterpillar Engines"
SEBF8101	Reuse and Salvage Guidelines, "Reuse and Salvage for C280 & 3600 Engine Cylinder Blocks"
SEBF9162	Reuse and Salvage Guidelines, "Inspection and Reconditioning Procedures of Main Bearing Bores in Cylinder Blocks"
SEBF9185	Reuse and Salvage Guidelines, "Cylinder Block Cleaning Procedure"
SEBV0544	Applied Failure Analysis, "Engine Bearings"
SMHS8418	Reuse and Salvage Guidelines, "Fundamentals of Flame Spray for Reconditioning Components"

Replacement Parts

Consult the applicable Parts Identification manual for your engine.

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When replacement parts are required for this product Caterpillar recommends using Caterpillar replacement parts or parts with equivalent specifications including, but not limited to, physical dimensions, type, strength and material. Failure to heed this warning can lead to premature failures, product damage, personal injury or death.

Measurement Requirements

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NOTICE
Precise measurements shall be made when the component and measurement equipment are at 20° (68° F). Measurements shall be made after both the component and measurement equipment have had sufficient time to soak at 20° (68° F). This will ensure that both the surface and core of the material is at the same temperature.

Section 1 – Bearings In Caterpillar Engines

The "Bearing Design" section covers a brief overview of the factors considered for selection of bearing materials, the construction of engine bearings, and how that construction relates to bearing performance. The "Engine Lubrication Systems" section explains why the lubrication system is important to bearing performance. The engine lubrication topic also details the consequences of lax maintenance of the lubrication system.

The "Other Systems Related to Bearing Performance" section explains how other engine systems can help or hinder the performance of engine bearings. Incorrect operation of the cooling system or air inlet system can cause bearing damage.

The "Early Recognition of Distressed or Damaged Bearings" section provides a few brief best practices to identify potential bearing distress or early stage damage. These suggestions can make replacing a damaged bearing before a catastrophic failure occurs possible but not guaranteed.

Bearing Design

Five factors are used in selection of bearing materials. These factors are compatibility, strength, wear resistance, conformability, and embedability.

Compatibility

Compatibility is the ability of the bearing material and the journal surface to function properly together in a bearing system, especially during periods of momentary contact. This property can be considered as an 'antiseizure' characteristic between the bearing and the journal surface. Ideal compatibility for a bearing material means that there is a minimum amount of friction between the bearing and journal. Compatibility also considers the chemical compatibility between the bearing materials and the engine environment, especially with engine oil.

Strength

Strength in a bearing material allows the bearing to retain shape and withstand the oil film pressures and loads from momentary contact with the journal.

Wear Resistance

Wear resistance of the bearing material ensures that the materials are present on the bearing surface at the end of useful life. Therefore, the properties of the bearing are consistent throughout useful life. Wear resistance requires some level of 'toughness' in the bearing material.

Conformability

Conformability is the ability of a bearing material to adapt or conform to the shape of a journal. The bearing material must be soft enough to conform to minor imperfections in the journal shape.

Embedability

Embedability of the bearing material allows absorption of small particles of debris. Bearings require a material that is soft enough for a limited number of small foreign particles to be absorbed by the bearing before damage to the journal occurs or disruption of the oil film.

Bearing Material Development and Selection

Bearing materials are developed to have a proper balance of the five material selection factors. Developing and selecting successful bearing materials is a significant challenge. This is due to the fact many of the selection factors require opposing properties. Such as, the 'soft' aspect for conformability and embedability against the 'toughness' for wear resistance and strength.

Different bearing materials have unique balances of these factors for different applications and uses. Some applications require maximum compatibility with moderate wear resistance, while other applications may require maximizing strength and wear resistance while allowing lower levels of compatibility.

There is no perfect and ideal mixture of the five material selection factors for all applications and uses. Therefore there are different bearing materials used throughout Caterpillar engines for the best match of the material properties to the application.

Bearing Construction

The main and connecting rod bearings in Caterpillar engines are made with layers of different materials. The layer construction provides the best way to optimize bearing material strength, conformability, wear resistance, conformability, and embedability. No one single bearing material layer can meet the needs of modern Caterpillar engines.

There are two main bearing construction types: 'bi-metal' and 'tri-metal.' These designations are based on the number of significant layers in the bearing construction. A bi-metal half-shell bearing consists of a steel back layer and an aluminum-based alloy running surface layer. A tri-metal half-shell bearing consists of a steel back with an aluminum-based or copper-based alloy layer and a thin 'overlay' covering the alloy layer. Thin material layers exist between the major layers including a bond or chemical dam layer between the alloy and the overlay. Typically, a similarly thin tin flash layer is applied all over the bearing top surface. The thin minor layers are not included in the nomenclature of 'bi-metal or 'tri-metal' designations.

Older Caterpillar engines have used 'solid' bearings that are one layer made of a babbitt material or an aluminum alloy. These types of construction are no longer used in modern Caterpillar engines.

Illustration 3	g03539949
Construction of a bi-metal bearing (A) Alloy Bearing Material (B) Steel Back

Illustration 4	g03538037
Construction of a tri-metal bearing. (B) Steel Back (C) Copper-lead or other alloy (D) Bond/Dam Layer (E) Lead-Tin Overlay and Tin Flash

Steel Back

The steel back gives strength, overall shape retention, and support for the alloy bearing layer. The steel back also makes other features possible. One example is "bearing crush" which will be discussed in the topic "Bearing Physical Features."

Bearing Alloy Layer

The first layer of bearing material applied to the steel back is either aluminum-based or copper-based material and called the alloy layer. The aluminum-based or copper-based alloy materials are developed and selected to balance the five requirements mentioned for the selection of a bearing material. Sometimes, the alloy layer provides bearing performance sufficient to meet an engine application need, and in that case a bi-metal bearing is specified.

The alloy layer has enough strength to withstand the heavy shock loads of engine operation. This layer is soft enough to provide good embedability and conformability. The alloy is also compatible with the steel of the crankshaft journal.

Lead-Tin Overlay

For applications where more capability over the alloy layer is required, an overlay layer is applied over the alloy layer. The overlay layer is typically a lead-tin based layer that is electroplated onto the bearing running surface.

The lead-tin based overlay is a thin layer and often 0.015 mm (0.0006 inch) to 0.030 mm (0.0012 inch) thick. However, in such a thin layer, the conformability, compatibility, and embedability characteristics of the bearing are improved over the alloy layer. And by limiting the lead-tin overlay layer to a small thickness, there is no noticeable decrease in overall bearing strength.

Another feature of lead-tin overlay is the ability to "heal over" (smooth out) when the surface is scratched by small particles. If a foreign particle makes a small scratch in the bearing, the life of the bearing will not normally be shortened. These small scratches will "heal over" during normal operation, however, this "healing" ability is limited to small particles. Large particles or a high count of small particles can lead to damage that is beyond the ability to "heal over". These particles will limit bearing life.

There are some special overlays that are aluminum-based, and used in unique applications. This type of overlay provides improved wear resistance in comparison to the typical lead-tin overlay

Tin Flash

On most bearing tri-metal bearings, a thin tin flash, 0.001 mm (0.00004 inch) to 0.003 mm (0.00012 inch) thick, is applied over the entire bearing as a final layer. This protects the bearing against corrosion during storage. The flash gives the bearing a light or dark gray color depending on whether a tin or lead-tin flash was used. This plating will show some cosmetic marks or scratches when handled, but this is normal.

Bearing Physical Features

Nomenclature of Caterpillar Engine Bearings

Consistent nomenclature is important when discussing main and connecting rod bearings. Understanding the physical features of a bearing will help during failure analysis and when corresponding with Caterpillar. Illustration 5 through 7 show the features that are part of a bearing.

Illustration 5	g03475158
Main Bearing (A) Tab Slot on ID surface (B) Edge of Bearing (C) Bottom Half (D) Top Half (E) Bearing Surface (F) Oil Groove (G) Oil Hole (H) Locking Tab on OD Surface (J) Mating Face

Illustration 6	g03475220
Connecting Rod Bearing (A) Tab Slot on ID surface (B) Edge of Bearing (E) Bearing Surface (H) Locking Tab on OD Surface (J) Mating Face

A locking tab helps locate a main or connecting rod bearing during installation. This tab fits in a slot machined into the mating part. Some engines with serrated connecting rods (rods with diagonal caps) do not use a locking tab for locating the connecting rod bearing. Instead, bearings for serrated connecting rods have a slot machined on the back of the bearing. This slot fits over a short dowel in the rod or cap bore. See Illustration 7.

Illustration 7	g03475261
Locating slot and dowel for serrated connecting rods. (K) Slot on Bearing Back (L) Dowel

Several features that are part of the upper half of the main bearing are necessary to provide correct oil flow. An oil hole in the bearing allows oil to flow from the block passages into the oil groove. The oil groove distributes the oil and maintains a continuous flow to the rod bearings. At one of the main bearing locations there will be a thrust surface in the front and in the back of the main bearing. The thrust surfaces control the axial movement of the crankshaft. There are two types of thrust bearings used in Caterpillar engines. The first type is designed so the thrust bearings and main bearings are one unit as shown in 8. The second type of bearing uses two thrust pates. One installed in the front and the other installed in the back of the main bearing as shown in Illustration 9 and Illustration 10. Thumbnail grooves or slots on the thrust bearings are used to distribute the oil over the thrust bearing surface.

Illustration 8	g03475381
Main bearing with thrust flanges

Illustration 9	g06313307
Thrust plates that are with a standard main bearing. (M) Thrust Plates (N) Thumbnail Groove

Illustration 10	g03475402

Bearing Spread

One of the design features of main and connecting rod bearings is called "bearing spread." See Illustration 11. Bearing spread simply means that the outside diameter of the bearing at the mating faces is slightly larger than the actual diameter of the bore.

Illustration 11	g03475560
Bearings are designed with a small amount of spread (P) Bearing Spread

Bearing spread requires a bearing to be lightly forced into place. Forcing the bearing into place helps retain the bearing firmly in the bore, during engine operation and during installation of rods or caps.

Bearing Crush

Bearing halves are made so the mating faces extend a small amount above the parting line of the bore. See dimension (Q) in Illustration 12. When the cap bolts are tightened, the bearing is fitted tightly in the bore, and an 'interference fit' is created between the bearing and the bore.

Bearing crush insures complete contact between the bearing and the bearing bore. This complete contact contributes to better heat dissipation and prevents movement of the bearing in the bore.

Illustration 12	g03475578
Bearing halves are designed to give bearing crush when bolted together. (Q) Bearing Crush

Engine Lubrication System

Bearing performance is determined by various factors. However, the most important factor is the engine lubrication system. Oil performs these vital functions.

• Reduces friction

• Provides an oil film cushion that keeps metal to metal contact to a minimum

• Cools the engine parts

• Cleanses the engine from particles and debris

The lubrication system for each engine may differ slightly, however most principles are the same. The lubrication system for the 3408 Engine is similar to many other engine lubrication systems as shown in Illustration 13.

Illustration 13	g03475617
Lubrication system for the 3408 Engine. (A) Bore for Camshaft (B) To Rocker Arm Shaft (C) Turbocharger (D) To Fuel Injection Housing (E) Rocker Arm Shaft (F) To Valve Lifters (G) Piston Cooling Tubes (H) To Timing Gear Housing (I) Oil Manifold (J) Bypass Valve for Oil Cooler (K) Oil Pump (L) Oil Pan (M) Oil Cooler (N) Oil Filters (O) Bypass Valves for Oil Filters (P) Bore for Balancer Shaft

As shown in Illustration 13, the oil pump sends oil through the oil cooler and then through the oil filters. The bypass valves for the oil cooler or oil filters protect the system if there is a restriction of the oil flow. When the engine is started with cold oil or the cooler or filter becomes plugged, the bypass valve assures a constant flow of oil to the engine. The bypass valve for the oil filters also protect against filter element damage that could result from starts with cold oil. However, it is important to monitor engine operation to ensure that operation with cold oil or with a plugged filter is kept to a minimum as operating the engine with the bypass open will place the bearing system at risk for debris damage and potentially bearing failure.

Oil from the filters flow into the block manifold or main oil gallery. This oil then flows into the various block passages to lubricate and cool the engine components. Then the oil returns to the oil pan. A detailed description of each lubrication system is given in the respective Service Manual for your engine

An understanding of the engine lubrication system can be helpful during bearing failure analysis. One example is when bearings are damaged due to lack of lubrication. If the failure is discovered at the appropriate stage, the bearings farthest from the oil supply will show the greatest damage. However, most times when a lack of lubrication failure occurs, the damage is not noticed until all bearings are severely damaged.

Oil Flow Through the Crankshaft

On many engines, the oil flow path through the crankshaft can give clues for use during failure analysis. Crankshaft rotation creates a centrifugal force on the oil in the passages that pushes the oil towards the rod bearings. On some vee engine crankshaft designs, there is a 'direct' drilling from the main bearing to one of the rod bearings and an 'indirect' or multiple intersecting passage drilling from the main to the other rod bearing. (Some crankshaft drillings are of a complex nature that both rod bearings are fed via an 'indirect' path.) If there is a lubrication failure, the rod bearings lubricated by an indirect path from the main bearing will most likely be damaged first. Wear caused by debris often may be more severe on the rod bearings that are lubricated by the direct passage.

The 3208 Engine is a good example of how the lubrication system design can give clues for failure analysis. Illustration 14 shows that if there is a lack of lubrication, the even number of rod bearings may have the greatest damage. If debris is the problem, it is likely that the odd number rod bearings will show the greatest damage.

Illustration 14	g03475676
Oil passages in the crankshaft for a typical V8 engine. (1) Main Bearings (2) Rod bearings

Although the principles involved with crankshaft oil flow are similar for all vee engines, the design of the oil passages might differ. Look at the crankshaft passages and draw a simple schematic of the oil passages. Then apply the principles of oil flow to determine what damage characteristics would be evident for your engine.

Oil Film

The oil that flows to the bearings forms an oil film between the crankshaft journal and bearings. This film provides lubrication, cooling, and cleansing for the bearings. A satisfactory oil film is critical to satisfactory bearing life.

Rotation of the crankshaft journal forces oil under the journal. This action lifts the journal off the bearing and, during normal engine operation, minimizes metal-to-metal contact. See Illustration 15.

Illustration 15	g03475684
Oil film between the crankshaft journal and bearing. (Q) Crankshaft Rotation (R) Oil Molecules Picked Up By Moving Crankshaft Journal (S) Oil Molecules Forced Between Crankshaft and Bearing (T) Oil Film (U) Bearing

Oil that flows across the bearing absorbs frictional heat that is created during crankshaft rotation as the oil separates the journal and bearing surfaces. The oil drains into the oil pan and then is pumped through the oil cooler. As the oil flows through the oil cooler, heat is transferred from the oil to the coolant. The cooled oil then flows through the filters back to the engine components.

Lubrication System Maintenance

Adequate bearing performance depends on the maintenance of the engine lubrication system. Maintenance will help keep the oil clean and free of contamination. Correct maintenance includes:

• Using oil of the correct grade and viscosity

• Maintaining the correct oil level

• Using the correct, high-quality oil filter

• Following the recommended oil and filter change intervals

Oil Viscosity

Lubrication system maintenance begins with the selection of the correct oil. The appropriate Operation and Maintenance or Lubrication and Maintenance Guide will give recommendations for oil grade and viscosity. Oil viscosity is one of the more critical oil properties.

Oil viscosity is the resistance of oil to flow or to change shape. The oil must have enough resistance to flow to maintain an oil film. However, the oil must flow sufficiently at all temperatures to insure an adequate oil supply to all moving parts.

Bearing failures can occur when oil of the wrong viscosity is used. Oil that has too high of a viscosity will not flow easily during cold starts. Cold starts with thick oil will cause excessive wear to engine bearings. If an oil has too low of a viscosity, the oil will not provide a sufficient oil film. An insufficient oil film will allow contact between the crankshaft journals and bearings, which will result in excessive wear of engine bearings.

Oil of a particular viscosity may perform satisfactorily during some temperature conditions. However, the same oil might not give a proper oil film when the oil temperature increases.

Oil Level

The use of the correct oil is not sufficient for adequate lubrication system performance. The oil must also be kept at the correct level. Check the oil level before and after each work shift. The Operation and Maintenance or Lubrication and Maintenance Guides provide instructions for checking the oil level (such as whether to have the engine running or not). Remember, operation of an engine with insufficient oil can result in severe bearing damage.

Oil Filter

Using the correct oil filter is important. Do not use a filter with a different part number than the recommended filter, even if the filter appears to fit. The filter element may be designed for a different application or the bypass valve setting may not be correct.

A high-quality oil filter is necessary to keep the engine oil clean and free of debris. Filters remove debris and particles from the oil before the particles can flow to the engine and damage the bearings. The use of a genuine Caterpillar filter is the best way to ensure that the oil filter performance will be satisfactory.

When a poor quality filter is used, poor filtration results. Some particles in the oil will not be removed by a poor quality filter. These particles then flow to the engine bearings (and other components) and cause damage or excessive wear.

Oil and Filter Change Intervals

There is no other maintenance as important as the regular changing of the oil and oil filters. This maintenance is necessary to rid the engine of contaminants (both debris and chemical corrosives) and to ensure that the oil maintains necessary properties to perform its functions. Each Operation and Maintenance Guide or Lubrication and Maintenance Guide shows the correct oil and filter change intervals.

Sometimes the consequences of extending oil change intervals are not clearly understood. Extending the filter change interval is not worth the risk involved if the filter should become plugged or damaged. Nor is extending the oil change interval worth the risk of oil additives being used up. Oil filters are designed to remove harmful debris particles from the lubrication system. Use of a filter beyond intended life can result in a plugged filter. A plugged filter will cause the bypass valve to open and can also cause filter element damage. A bypass valve that stays open for extended periods, can cause engine damage. Oil is not filtered when the bypass valve stays open. Any debris particles in the oil will flow directly into the engine. When a bypass valve remains open, the particles that were previously trapped by the filter may be flushed from the filter and through the open bypass valve and straight to the bearings.

Illustration 16	g03476186
An example of bearing debris damage that can occur when the filter is plugged.

Filter plugging can also cause distortion of the filter element. A distortion happens when there is an increase in the pressure difference between the outside and inside of the filter element. This distortion can progress to cracks or tears in the paper. Cracks or tears in the filter element allows debris to flow into the engine where debris can damage various components. Engine bearings are especially susceptible to debris damage.

Extended oil change intervals will also cause the oil to deteriorate or break down. Extended use of the oil will cause the additives to be depleted or "used up." Engine oils have additives that perform several functions. One function is to help neutralize the acids that are formed during combustion. Depleted oil additives can result in engine damage (in the form of bearing corrosion, as one example) as more acids are formed.

Illustration 17	g03476196
A filter that was used beyond the normal change interval.

Engine oil additives are also used to disperse the very minute particles that are carried in the oil. The oil filter removes large, damaging debris from the oil. However, very minute particles can pass through the oil filter. The added dispersants in the oil prevent a conglomeration of these minute particles that could cause engine damage.

Remember, satisfactory bearing performance depends on correct maintenance to the lubrication system. Follow the recommendations given in the appropriate Operation and Maintenance or Lubrication and Maintenance Guide. Continued violation of these maintenance practices will result in a shorter life for the engine components.

Other Systems Related to Bearing Performance

Cooling System and Bearing Performance

The operation of the cooling system also affects engine bearing performance. Satisfactory operation of the cooling system helps maintain the correct engine oil temperature. A cooling system malfunction that results in an overheated engine will cause a corresponding increase in the oil temperature. High oil temperatures reduce the viscosity of the oil and reduce the oil film thickness between the crankshaft journals and bearings. When the viscosity of oil is reduced, the oil film will not carry the loads caused by combustion. High oil temperature can allow excessive bearing wear as the crankshaft journals contact the bearings.

Leakage of coolant into the engine oil is another problem that can cause poor performance of engine bearings. Leakage can happen when oil cooler seals fail or when head gaskets fail. Coolant leakage can be discovered at an early stage, before excessive bearing wear occurs. Scheduled Oil Sampling often discovers coolant in the oil at an early stage before any major damage has occurred.

When coolant combines with oil, the coolant reacts with the oil to form a thicker oil. The reaction causes a sludge to form because of the release of combustion particles that were previously held in suspension. Sludge and thicker oil creates an oil film problem because the oil will not flow easily. The sludge can also cause the filter to become plugged.

Air Inlet System and Bearing Performance

Air filtration is the most important factor when considering the relationship between the air inlet system and engine bearing performance. Dirt can enter the engine if air filtration component maintenance is not correct, or if there are leaks in the air inlet system.

When dirt enters the engine through the air inlet system, the piston rings and the cylinder bore are first to show damage. However, some of this dirt can eventually get into the lubrication system where the dirt can flow to the engine bearings. The resulting bearing damage is typical of debris damage: scratches, embedded material, and accelerated wear.

The Operation and Maintenance of Lubrication and Maintenance Guide for each engine shows the maintenance practices that are necessary for the air filters. Compliance with the maintenance recommendations will contribute to satisfactory engine performance.

When performing maintenance on the air inlet system, the connections should be checked. Loose connections can allow dirt to enter the engine. Make sure that all connections are tight.

Early Recognition of Distressed or Damaged Bearings

A bearing is distressed or damaged when there are negative attributes (observed features) found in the bearing that may lead to a bearing seizure. Examples of distress or damage are severe or extensive debris scratching, smear and / or scuff of the bearing material. Bearing polish or slight wear, however, is a normal phenomenon of bearings and is not considered a failure. High wear rates can have a negative impact on bearing system robustness if wear occurs before full life is achieved

Recognition by Engine Symptoms

An engine will give two common signals when bearings are damaged. The two common signals are an engine knocking noise and low oil pressure. A knocking noise usually means that at least one bearing is severely damaged. The engine oil pressure can sometimes be an indication of excessive bearing wear or damage. Bearing wear is not a failure, but bearing damage can lead to bearing seizure where the engine will no longer operate. As the bearing wear increases, the clearance also increases between the crankshaft and the bearing. The increased clearance allows more oil to flow out the sides of the bearing and the oil pressure will be less. Increased clearance can also result from a damaged bearing. Thus, reduced oil pressure can be an indication that there is excessive bearing wear or damage.

Recognition by Scheduled Oil Sampling

Scheduled Oil Sampling (SOS) is a good way to monitor engine condition. Oil analysis can identify an excessive number of wear particles in the oil. When considering only the engine bearings, the most important function of Scheduled Oil Sampling is to determine if there are any contaminants in the oil. Oil contaminants include: dirt/debris, coolant, or fuel. All these contaminants can cause bearing damage. Scheduled Oil Sampling can find these contaminants at an early stage, before damage or failure occurs.

Recognition by Oil Filter Examination

Inspection of the oil filter element with each filter change is a valuable check for bearing damage. Filter element inspection will show if there is an excessive amount of debris in the oil system. If there is excessive debris, the bearings may be worn excessively or damaged. The inspection of the filter may also reveal bearing material trapped in the filter. Bearing material in the oil filter can indicate a badly worn or damaged bearing. Bearing problems may be found an early stage by regular examination of the oil filter.

Conclusion

Main and connecting rod bearings play an important role in diesel engine operation. Engine bearings are designed to support the crankshaft and connecting rods with a minimum amount of friction. Bearings also have to withstand the severe conditions imposed by the combustion process.

The ability of engine bearings to withstand the severe conditions depends on the oil film. To assure a correct oil film, the engine lubrication system must be maintained properly. The correct oil and filter must be used. The oil level must be maintained at the proper level. The recommended oil and filter change intervals must be followed.

Remember, maintenance recommendations are given so the engine user can achieve maximum service life of the engine. Avoiding the maintenance or extending the maintenance intervals is not a practical way to cut costs. The probability of a shortened engine life and the cost of a major overhaul are not worth the risk.

Section 2 - Overhaul of the Engine Lower Structure

Contents of Section 2

"Section 2 - Overhaul of the Engine Lower Structure" provides recommendations to follow during overhaul of the engine lower structure. "Section 2 - Overhaul of the Engine Lower Structure" is not intended to be all-inclusive. "Section 2 - Overhaul of the Engine Lower Structure" must be used with other service literature such as Service Manuals and/or Engine Assembly Charts. Other parts of the engine, such as upper structure or front structure, are not discussed in this section except as to relate to the lower structure or to bearing performance.

During engine overhauls, simply replacing old parts with new ones is not enough. Examination of the removed parts, correct analysis of failed parts, and correct reconditioning of components are all necessary for successful engine overhauls.

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NOTICE
Be careful when reassembling the engine components. Any debris assembled into the engine can significantly damage the engine components.

Preparation for Disassembly

Before disassembly work is started, always determine how extensive the overhaul must be. If the engine has failed, the cause of failure must be found and corrected. Some preliminary inspections and evaluations will help determine what work must be performed on the engine.

The extent of the overhaul is determined by the amount of wear and/or damage to the engine components. If any machining must be performed on the engine block or crankshaft, an extensive overhaul must be performed. An extensive overhaul is done with the engine removed from the engine mounting. If no machining work must be done, the overhaul can probably be done with the engine at the installed position. However, some engines may still need to be removed from the engine mounting for a less extensive overhaul because of space limitations.

If the engine has experienced a failure, get operating information from the operator. How was the engine being operated at the time of failure? Were there any significant changes in oil pressure or engine temperature? What were the symptoms during the failure?

If a main or rod bearing failure is suspected, see "Section 3 - Inspection Guide and Failure Analysis for Main and Connecting Rod Bearings"." "Section 3 - Inspection Guide and Failure Analysis for Main and Connecting Rod Bearings" provides an overview for basic failure analysis steps and contains illustrations of common bearing appearances.

Obtain the history of the engine. Check recent Scheduled Oil Sampling findings. Check to see if any recent overhauls or repairs were performed. Always examine the external components of an engine before disassembly work is started. Examining the exterior of an engine may help identify failures and may also help to determine how extensive the overhaul should be. During the examination ask the following questions:

• Is there any indication of oil, fuel, or coolant leakage?

• Are any external parts broken?

• Are all lines tight and installed correctly?

Next, remove the oil filter and inspect the filter element for damage, plugging and/or foreign material. Material in the oil filter can give an indication that a bearing failure has occurred.

After the external inspection has been completed, thoroughly clean the engine with steam or a high-pressure wash. If the engine has suffered a ventilation, care must be taken to seal the opening prior to washing to ensure that water does not contaminate inside the engine, if it has not already occurred either from transit to the disassembly area or from environmental exposure. Removal of all oil and dirt will make disassembly easier and ensures that no dirt will get in the engine during Disassembly and Assembly. Cleaning should be done in a separate area than the Disassembly and Assembly area. Some engines, such as marine engines, cannot be thoroughly cleaned before an "in-frame" type overhaul is performed. When this type of overhaul is performed, clean the engine as much as possible. As you work, make sure that no external dirt/debris enter the engine.

Disassembly of Engine Lower Structure

If a failure has occurred, special care taken during disassembly will make analyzing the actual problem easier. If you are not careful during disassembly, you may destroy clues that may have shown why the failure occurred.

Use a SOS bottle to save some of the crankcase oil. Use the crankcase oil for later analysis (if necessary). The results of the analysis can reveal the presence of fuel, coolant, or dirt in the oil. The analysis can determine whether the engine had received correct maintenance. Remember, successful engine overhauls require a clean work area. Oiled parts "attract" the dust in the air and the dirt in the work area. Dust, dirt, or debris assembled into the engine can cause failure of the main and connecting rod bearings.

When disassembly work is performed, keep the removed parts neatly arranged. A parts cart or similar equipment is useful to maintain an organized work space. See Illustration 18. Mark any tubes or hoses when disconnected. Keep miscellaneous hardware together with the components. Prevent loss of parts or damage to parts during storage.

Illustration 18	g03476231
Parts cart used for storage of removed parts.

Before removal of the main or connecting rod bearings caps, check the markings. Connecting rods and the mating caps should have the rod location number stamped or etched near the parting line. See Illustration 19. Main bearing caps should be marked with the respective number location. The same number is sometimes stamped on the block next to the cap. Other engines have main bearing caps with a number location marked and an arrow that must always point toward the front of the engine.

Illustration 19	g03476242
Marks on main bearing caps and connecting rod caps for a 3406 Engine.

All these marks are important for use during assembly. If the marks are not clear, make new ones. The orientation of the marks with the crankshaft and the block is important. Use the marks to make sure that the caps are installed on the correct rod or block saddle. Make sure that the caps are not reversed. The marks for the connecting rods must be on the same side of the crankshaft as the marks were when the rods were removed. Before loosening the bolt or nut, mark the bolt on one corner and put a corresponding mark on the cap. Marking the bolt and the cap will enable you to determine if the torque was correct during previous assembly. Remember, a bearing failure may have been caused by bolts that were not tightened correctly.

Initial loosening of the bolt or nut must be done with a hand wrench, if the torque is to be checked. If the bolt clamp load (preload at assembly) is to be verified or if the torque does not feel correct when loosening the bolt or nut, it should then be checked. There are two main methods to provide bolt torque verification: the first is 'return to mark' and the second is 'breakaway torque.' Return to mark is the preferred method as the breakaway method inherently has significant variability due to static friction variation.

There are two ways to apply the 'return to mark' method. Both methods utilize the marks applied to the bolt head and to the abutment (connecting rod or main cap) that were previously described. To do the first return to mark method, use a torque wrench and tighten the bolt or nut to the correct torque specification. If the original torque was correct, the distance from the mark on the bolt to the mark on the cap must be equal to the turn specification. As an example, if the torque-turn specifications are 136 N·m (100.3lb ft) plus an extra 180 degrees, tighten the bolts to 136 N·m (100.3lb ft). Then compare the two marks. The two marks must be 180 degrees apart if the initial torque was correct. The breakaway torque verification method requires the use of a digital or dial indicator torque wrench to ensure measurement of the initial torque value as the bolt head moves. This method can either be used to measure torque on the bolt upon loosening or the torque required to move the bolt head upon further tightening. Use of the loosening method is recommended as over-torque of connecting rod or main bolts is ill-advised and may damage the components. Furthermore, the breakaway method will only provide a rough indication that there was sufficient torque applied to the bolt. This method will not provide the exact torque due to friction variation. Only use the breakaway method to verify that the measured values are above the torque values used in the torque-turn assembly process.

Use caution during removal of the bearing caps and connecting rods so the crankshaft journals are not damaged. Make sure that the threads on the connecting rod bolts do not scratch the journals. A short piece of hose over the threads can protect the journal.

Illustration 20	g03476248
Use of the bearing removal tool.

If an overhaul is done with the engine in frame or in engine mounting, tools such as the 2P-5571 2P-5518 Bearing Removal Tool can be used. See Illustration 20. These tools can be used to "roll out" the upper half of the main bearings with the crankshaft still installed.

When the rod and main bearings are removed, mark location in the engine. Keep the bearings together in sets of rod bearings or main bearings.

Illustration 21	g03476251
These bearings do not have any marks. Determining the correct location of the bearings in the engine will be impossible.

Illustration 21 shows unacceptable packaging for engine bearings.

Inspection

If a bearing failure has occurred, refer to "Section 3 - Inspection Guide and Failure Analysis for Main and Connecting Rod Bearings". "Section 3 - Inspection Guide and Failure Analysis for Main and Connecting Rod Bearings" describes common causes of bearing failures. "Section 3 - Inspection Guide and Failure Analysis for Main and Connecting Rod Bearings" also shows how to prevent repeated failures.

Remember when bearings are removed, whether failed or not, learn how to "read the iron." What characteristics are shown by the wear patterns? Do the parts give an indication of what caused the failure? Installation of new parts is not enough. Take steps to prevent a repeat failure.

Measuring Components

An engine will normally be disassembled for one of two reasons: when an engine has high hours, thus reaching service overhaul service, or when an engine has experienced a failure.

On the engines that are overhauled due to high hours, examine the bearings and crankshaft for indication of irregular wear patterns. The wear pattern can indicate how thorough the measurements must be before installation of new parts. An irregular wear pattern can be caused by several things:

• A profile problem on the crankshaft journal

• A bent crankshaft

• Main bearing bores that are not in alignment

• Or main and rod bores that are not round

• If irregular wear patterns are evident, all mating parts must be measured to find why the bearing wear is not normal.

On the engines that are being overhauled because of a bearing failure the mating parts, if appears to be reusable, must always be measured for distortion or for irregular wear. Many times, failures cause excessive heat which distorts parts. Also, when bearings fail, the wear pattern is destroyed. There is then no way the bearing can reveal whether the wear patterns were normal. Lack of this information requires the mating parts to be measured.

Component Measuring and Reconditioning

Refer to the proper Service Manual and/or Engine Assembly Chart for the proper measurements and reconditioning procedures. Several reference Reuse and Salvage Guidelines are provided below for crankshaft, connecting rod and block.

• M0080689Reuse and Salvage Guideline, "Cylinder Block Cleaning and Audit Procedure"

• , SEBF8042Reuse and Salvage Guideline, "Reuse and Salvage for Crankshafts"

• , SEBF8101Reuse and Salvage Guideline, "Reuse and Salvage for C280 & 3600 Engine Cylinder Blocks"

• , SEBF9162Reuse and Salvage Guideline, "Inspection and Reconditioning Procedures of Main Bearing Bores in Cylinder Blocks"

• , SEBF9185Reuse and Salvage Guideline, "Specifications and Salvage for Cylinder Blocks in C175 Engines"

• , SMHS8418Special Instruction, "Cylinder Block Cleaning Procedure"

Assembly of Lower Engine Structure

Before starting to assemble the engine, several questions must first be answered:

• Was the engine disassembled at normal overhaul?

• If a failure occurred, was the cause of the failure found and corrected?

• Were other mating parts damaged?

• What problems were noted when the engine was inspected externally and internally?

• Did you "read" the iron?

• Were all the problems corrected and components reconditioned?

All the above are important considerations during overhaul of the lower structure

Preparation for Assembly

During the final operation, assembly of the lower structure, cleanliness of utmost importance. The "Disassembly" topic of "Section 2 - Overhaul of the Engine Lower Structure" mentioned that a clean work area is essential. This point is significant enough to repeat. Successful overhauls demand a clean work area. Do not assemble debris into the engine. Cleanliness is a major factor in reducing repeated bearing failures.

Approximately 50 percent of all bearing failures are cause by debris in the engine. One source of debris is an unclean work area. Another possible source is machine particles that are left in individual components after machining operations. Another possibility is debris produced during a bearing failure. This type of debris is circulated through the lubrication system of the engine. There is only one way to remove any of the debris from the engine, which is a complete cleaning of all components.

The components must be cleaned whenever machining has been done or whenever there is a bearing failure. After machining, remove all plugs and clean the oil passages with brushes. Extra care must be taken after a bearing failure to make sure all the debris and bearing material is removed from the engine lubrication system. The crankshaft oil passages must be cleaned. All plugs, orifice dowels, cooling jets and hoses must be removed from the block so the oil passages can be cleaned. Remove auxiliary equipment that is lubricated by the engine oil. Disassemble this equipment and clean the oil passages. Oil coolers cannot be cleaned if contaminated by a bearing failure. The oil coolers must be removed and new ones installed.

Cleaning the components to remove the debris must be done with brushes and a cleaning solution. See Illustration 22. The brushes must be the correct size for the oil passage being cleaned. For a cleaning solution, first use an oil-based solvent, then use the brushes with a detergent and water. The detergent and water will "float" the particles out of the oil passages. After rinsing the cleaning solutions from the passages, coat the machined surfaces with oil to prevent corrosion.

Refer to , M0080689Reuse and Salvage Guideline, "Cylinder Block Cleaning and Audit Procedure" to clean the cylinder block.

Illustration 22	g03476282
Use a brush to clean the oil passages.

Wipe parts clean before installation. If new bearings are kept in the original box until installation, the bearings should be clean. If the bearing is determined to be clean from the box, the bearing should be installed as found in the package and not cleaned. However, if the bearings have dust or dirt on the running surface (ID) from storage, the running surface should not be wiped clean. Wiping the bearing running surface could cause the dust or dirt to become embedded in the bearing surface. To clean bearing running surfaces, put them in a solvent tank. The bearing surface can then be rinsed and blown dry. If the bearing has debris on the backside of the bearing, on the steel back, use a proper solvent, such as Brake Clean, and a lint free rag to clean the new bearing back. Apply a light film of clean oil to back of bearing surface using a clean rag and a generous amount of oil on the front of each bearing. The bearing may now be installed into position. Be sure to follow the proper Service Manual and/or Engine Assembly Chart.

Assembly of the Lower Structure

When the parts are installed, be careful not to damage any machined surfaces. Check the markings on the bearing caps and make sure that the bearings are installed in the original location and orientation. Other things to remember during assembly:

• Check the parts for burrs that may cause the parts to seat incorrectly.

• Ensure that bearings are clean from the packaging or follow proper procedures to clean and oil the bearings.

• Make sure the nuts or bolts for the bearing caps are tightened by using the correct torque-turn procedure.

• Always check the torque values list in the Specifications section of the Service Manual or on the Engine Assembly Charts.

• Check to see if the crankshaft turns freely.

Measurement of Bearing Clearances

If the crankshaft journals and bores were measured at disassembly and found to be within specifications, no more measurements of the bearing clearance are needed.

Note: Caterpillar does not recommend the checking of the actual bearing clearances. This is because of the possibility of obtaining inaccurate results and the possibility of damaging the bearing or the journal surfaces. Each Caterpillar engine bearing is quality checked for specific wall thickness.

However, if the service technician still wants to measure the bearing clearances, refer to the Disassembly and Assembly Manual for your engine and see the "Bearing Clearance – Check" procedure.

Engine Run-In After Overhaul

After an engine is overhauled, a good practice to "run-in" the engine on a dynamometer, if possible, following the Caterpillar , SEBF9011Reuse and Salvage Guideline, "Dynamometer Testing of Caterpillar Engines". It is recognized that run-in on a dynamometer is not possible in every circumstance, but it is best practice to ensure that a successful engine reinstallation procedure is achieved after an overhaul.

The run-in test or dynamometer testing procedure is intended to allow the new parts to wear-in together in a controlled manner. This procedure also makes it possible to check for leaks and make necessary corrections. The power settings, correct pressures, and temperature can be checked during dynamometer testing. Adjustments can be made in the dynamometer test cell before engine installation into the application.

Conclusion

Following the recommendations in Section 2 will contribute to successful overhauls. Repeat failures, especially at low hours, are costly. If the correct procedures are used during each overhaul, with an emphasis on cleanliness, these repeat failures will be reduced. Remember, quality overhauls are a vital part of a successful engine service operation.

Section 3 - Inspection Guide and Failure Analysis for Main and Connecting Rod Bearings

Introduction

"Section 3 - Inspection Guide and Failure Analysis for Main and Connecting Rod Bearings" provides technicians with information needed to interpret correctly the appearance of used bearings or analyze failed (seized) bearings. Illustrations show what is considered normal or typical features found on used bearings plus several common causes of seizure. While the information contained in this section covers most expected observations, it is not possible to anticipate every potential observation of bearings herein.

For technical questions when using this document, work with your Dealer Technical Communicator (TC).

To report suspected errors, inaccuracies, or suggestions regarding the document, submit a form for feedback in the Service Information System (SIS Web) interface.

Familiarity with both the illustrations and the observation description in this guide will help in understating the appearance of the bearings or in determining the cause of bearing failure (seizure). Suggestions are also given for corrective measures that can reduce the possibility of a repeat failure.

A bearing failure is a seizure of the bearing to the journal, and the engine is not capable of operation. A damaged bearing is one that has features that could lead to seizure but has not seized. Damaged bearings are not failures of the bearing system but possess characteristics that might or might not be detrimental to future operation. In many instances, a damaged bearing will, and does survive to overhaul with the damage present. Examples of damaged bearings would be debris scoring to the alloy layer or smear of the overlay. Bearings with wear through the overlay or cavitation erosion typically are not damaged bearings, unless the wear of cavitation erosion is extreme.

Each bearing investigation is different. Some assessments of used bearings or failures require more investigation than others. If correct procedures and sequence are used after each bearing inspection, there will be more success in analyzing and correcting the cause of bearing failures. A list of bearing inspection steps is given for this reason.

As stated in Introduction of this guideline, whenever a bearing is inspected (beyond short hours of operation), it is the recommendation of Caterpillar to replace the bearings. It is necessary to ensure that both halves of the bearing are replaced.

Inspection Procedures

Careful and deliberate visual inspection of all bearings, journals, and bores (block main bore or connecting rod bore) is necessary to understand properly the appearance of bearings at inspection.

It is also important to collect information on the engine and / or machine operational history to accompany the visual information and inspections. A partial list of such information is:

• Engine family

• Application

• Location (in world) of engine / machine operation

• Engine and machine serial number

• Engine / machine and bearing hours

• Bearing part numbers

• Engine history, to the extent possible SOS data

Identification, Picture Preparation, Removal & Cleaning, Bearing Layout, and Packaging

Accuracy in the identification of bearings, care in the cleaning, properly laying out the bearings, quality photography, and careful packaging for shipment for further analysis is vital if the visual inspection is to be exact. The examples below shows a 20-cylinder engine but the process can be used for other engine sizes.

Packaging

Illustration 23	g03481176

If a bearing must be shipped or stored, be sure that the bearing is protected correctly. Package bearings individually to ensure that they do not get damaged. Itis recommended to wrap each bearing individually in a thick clean paper towel or clean disposable shop towel with the wrapping secured with an adhesive tape. Do not allow bearing surfaces to touch other bearing surfaces. Illustration 23 represents a properly protected bearing.

It is not recommended to tape the back of the bearings to form a row of bearings for inspection. This procedure can damage the bearing backs and that will not allow proper inspection of the bearing back. Taping the bearing backs together also does not allow the most robust packaging to avoid damage in shipping.

Identification

As a start of the inspection process, identification must be made at the time the bearings are removed. The bearing layout will set the bearings in a manner where they align on the table as they did in the engine. This will help identify and understand wear patterns, and other conditions across the entire bearing set. Due to variations in engine design, each of these engine families has a different layout procedure, it is important to use the correct procedure for the bearings being inspected.

Picture Preparation

On the table in front of the bearings write the bearing numbers in line with the bearings. Write the claim or work order number, engine serial number, bearing life in hours, and machine number if available. Also include the SIB number when possible. When sharing is needed, images should be transmitted in their original format and size, use Cat SIFT if several photos are being shared. When harsh overhead lighting is present, with a helper use a large piece of cardboard, an opaque engine cover blanket, or other cover to prevent glare on the bearings. Take pictures from several angles to help highlight specific features.

Removal and Cleaning

Clean bearings with a solvent such as Stanisol by flowing the cleaning fluid over the bearings to wash away engine oil and contaminants. The bearings can also be cleaned with a solvent such as Brake Clean. Caterpillar recommends using these solvents, and these solvents are recommended because of quick evaporation. The use of gasoline is too dangerous and is not recommended. The use of diesel is restricted by a slow rate of evaporation. If another solvent is used, the solvent must be of a type that does not damage steel, lead, tin, copper, aluminum, or nickel.

Never use rough materials, brushes or mechanically wipe on the ID or running surface of the bearing to clean it. Do not use sandpaper, emery polishing paper, crocus cloth, files, brushes, glass beads, soft cloth, or paper cloth to clean bearings. Identification marks that have been removed during cleaning must be recorded again.

1. Wearing clean gloves, remove the bearing from the box or connecting rod. For connecting rods on the bench it is best to twist out the bearing by pressing the side (near the apex) of the bearing axially rather than roll the bearing out along the circumference of the bearing. Try to avoid touching the front or rear faces of the bearing. Do so by gripping the sides of the bearing.
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   Illustration 24	g03481158

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   Illustration 25	g03481159

2. Keep both halves of the bearing together. If possible, write "U" for upper half and "L" for lower half bearings and the number of the bearing in the tab area as shown in Illustration 24 and 25. Use a ballpoint of felt tip pen to make the identification mark. If you cannot make the mark in the tab area, mark the back of the bearing as shown in Illustration 25. For main bearings, use the number of the main bearing cap. For connecting rod bearings, use the number of the cylinder. Limit identification marks to the area next to the mating face. Do not write the identification on the running surface other than in the tab slot area.

3. With a soft towel gently remove any oil left on the bearing running surface, to improve photo quality. Do not damage running surface or drag away imbedded debris with towel. This is best performed by using a dabbing motion. Any wiping motions should follow the crankshaft movement. In other words wipe around the bearing, not across the bearing.

4. To clean the backside, dab with dry towel or roll back the bearing and forth on a dry towel, (no sliding) similar to making a fingerprint. This will adequately remove any unwanted debris and oil, with minimal impact on carbon signature.

3500 Rod Bearing Layout

The benefits of a proper bearing layout include photos that properly represent the bearing set in a meaningful way for analysis, and commonality. As bearing analyzers gain experience looking at bearing sets they will gain a better understanding of what ‘normal’ looks like, and more easily identify abnormal patterns or conditions. When bearing photos are shared with the factory through DSN or other communications, it is important to have them laid out in a meaningful way for bearing experts to review.

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Illustration 26	g06315177
Example of 3500 Rod Bearing Layout

1. Lay the bearings out with cylinder one to the left, running side up. The bearing tabs should be staggered with bearing 1 tabs on the inside, and bearing 2 tabs on the outside and so on, tabs indicated by the red lines shown in Illustration 26.

2. This layout should represent how the bearings actually sit in an assembled engine, assuming upper shells are hinged about the edge where they touch the lower shell in the layout to close the circle.

Illustration 27	g06315182
Example of proper 3512 rod bearing cleaning and layout. Wear patterns are easily observed.

Illustration 28	g06315359
Overview of rod bearing set from 3512 engine. Although, proper cleaning has been practiced, layout pattern is incorrect (all tabs aligned toward top). This layout hinders assessment of wear pattern.

3500 Main Bearing Layout

Illustration 29	g06315185
Example of 3500 Main Bearing Layout

The main bearings should be laid out in a similar fashion to the rod bearings, except the tabs are all oriented to the outside, indicated by the red lines shown in Illustration 29.

Illustration 30	g06315186
Example of 3512 Main Bearings.

C175 Rod Bearing Layout

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Illustration 31	g06315189
Example of C175 Rod Bearing Layout

1. Lay the bearings out with cylinder one to the left, running side face up. The bearing tabs should be positioned on the inside, indicated by the red lines shown in Illustration 31.

2. This is the standard procedure for the C175 platform, it may not resemble the actual layout of the engine.

C175 Main Bearing Layout

Illustration 32	g06315345
Example of C175 Main Bearing Layout

The main bearings should be laid out in a similar fashion to the C175 rod bearings; the tabs are all oriented to the inside, indicated by the red lines shown in Illustration 32.

3600I Series Rod Bearing Layout

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Illustration 33	g06318060
Example of 3600I Series Rod Bearing Layout

1. Lay the bearings out with cylinder one to the left, running side face up. The bearing tabs should be positioned on the outside, indicated by the red lines shown in Illustration 33.

2. This layout should represent how the bearings actually sit in an assembled engine.

C280/3600V Series Rod Bearing Layout

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Illustration 34	g06315350
Example of C280/3600V Series Rod Bearing Layout

1. Lay the bearings out with cylinder one to the left, running side face up. The bearing tabs should be staggered with bearing 1 tabs on the outside, and bearing 2 tabs on the inside and so on, indicated by the red lines shown in Illustration 34.

2. This layout should represent how the bearings actually sit in an assembled engine.

C280/3600 Series Main Bearing Layout

Illustration 35	g06315345
Example of C280/3600 Series Main Bearing Layout

The main bearings should be laid out in a similar fashion to the C175 rod bearings; the tabs are all oriented to the inside, indicated by the red lines shown in Illustration 35.

This information, when used with , SEBV0544Applied Failure Analysis, "Engine Bearings", will help the analyst understand normal and abnormal wear patterns and conditions in connecting rod bearings and main bearings for 3500, C175, and C280/3600 Series Engines.

Overview of Bearing Attributes

All used bearings will have some characteristic appearances or features present, which result from use in an operating engine. These characteristics and features are called bearing attributes. Only a few of these attributes or severe attribute appearances are classified as a damaged bearing. Some attributes found on bearings are:

• Overlay or alloy polish

• Wear

• Smear

• Debris scratching

• Cavitation Erosion

Bearing Wear and Polish

Before discussing any other bearing attribute, damage or failure, it is important to recognize normal wear. Bearing wear occurs on all bearings, and asking 'does the wear pattern look normal and well distributed?' should be the first question during the visual inspection of bearing.

Bearing wear is result of polishing due to contact between the journal and the bearing surface. Polishing occurs when the oil film thickness between the bearing and crankshaft journal decreases for a short time. Polishing first appears as a shining of the top bearing layer. As engine hours accumulate, the polishing will gradually spread over the loaded portion of the bearing surface and will also progress through the various bearing layers. This occurrence of polishing and wear is normal.

Each type of bearing has a specific area which normally wears the most. While heavy wear is expected in this location, known as the "load area", the bearing must still be carefully inspected. Illustrations 36 and 37 show the location of load areas for connecting rod bearings. Illustration 39 shows the location of load for main bearings.

Illustration 36	g03476365
The load area for bearings used in standard connecting rods.

Illustration 37	g03476382
The load area for bearings used in serrated connecting rods.

Connecting rod bearing wear is not located in the center (in relation to the mating faces) but instead on the one side of the load area. Wear is also heavier in the upper half of the bearing as shown in the following illustrations. The connecting rod bearings in Illustration38 show wear that has processed into the overlay layer. This is acceptable wear.

Illustration 38	g06315143

In comparison, the load area and the wear on main bearings is normally heavier on the lower half.

Illustration 39	g03476405
The load area for main bearings.

Illustration 40 shows a typical main bearing set that shows wear into the overlay layer, and some embedded debris that has 'healed' over. This is acceptable wear.

Illustration 40	g03476551

Illustration 41 shows a close-up view of an example upper rod bearing (#4 Bearing from Illustration 38). The bearing shows the reproduction of the journal profile (shape). The wear pattern is relatively straight across the bearing surface. This indicates an acceptable journal profile. The number 4 upper rod bearing also shows the wear caused by polishing. The color variations are caused by the progression of wear through the different layers of the bearing. Polishing is a normal condition that progresses with engine life.

Illustration 41	g03477283

The shape of mating parts often contributes to the wear pattern on bearing. Shape variation of the mating parts, both within specification and outside specification, or parts not installed properly can create an irregular bearing wear pattern. In severe cases, an irregular wear pattern can result in greater sensitivity to debris, oil contamination, or lack of lubrication that can increase seizure potential.

Illustration 42	g03477359
Thin oil film that can be caused by a barrel shaped crankshaft journal.

There are several possible causes for irregular wear patterns. Some are:

• Crankshaft journals with profiles that are not straight and/or not finished to correct specifications

• Main bearing bores in the block are not in alignment or not round

• Rod bores that are the wrong diameter or not round

• Rod pin bore and bearing bore that are not parallel

• Parts were not installed correctly at the previous assembly. Example: Bearing caps that were interchanged or reversed

• Bolt torques that are not correct

Illustration 43	g06315149

The bearing shown in Illustration 43 was damaged by a bad profile of the crankshaft journal. The drawing also shows the corresponding journal profile that would produce this wear pattern.

Illustration 44	g03477500
Normal journal profile with normal bearing wear.

Illustration 45	g03477502
Barrel shaped journal with the corresponding bearing wear.

Illustration 46	g03477503
Hourglass shaped journal with corresponding bearing wear

Illustration 47	g03477505
Tapered journal with corresponding bearing wear.

Irregular Shape or Profile of Crankshaft Journal

Crankshaft journals that have bad shapes or profiles (out of specification) can cause bearing failures because of uneven oil film thicknesses. If the journal profile is not correct, some areas of the bearing may have an oil film that is not sufficient to lubricate the bearing or carry the heat away. This can cause extreme heat on some areas of the bearing which can then result in a bearing failure. See Illustration 42 through Illustration 47.

Many times a poor journal profile can combine with another problem to cause a bearing failure. As an example, a journal may have a bad profile that causes an irregular oil film and irregular wear pattern, but no failure. If debris enters the lubrication system, the combination of debris and a poor profile may cause a failure.

Misalignment of Main Bearing Bores

Bearings can fail because the main bearing bores are not aligned. With misaligned bores, the crankshaft journal may rotate at an angle in the bore. Angular rotation causes heavy loads on a small area of the bearing and a decreased oil film at the edges of the bearing.

If a bore is only slightly misaligned, the bearing may conform to the position of the journal. However, as with a bad journal profile, the bearing may be more sensitive to debris or other problems.

Illustration 48	g03477856
This bearing has a wear pattern caused by a main bearing bore out of alignment. Notice how the wear pattern is heavier on one side and runs diagonally across the bearing.

Parts Assembly Impact to Irregular Wear

Incorrect assembly of parts usually involves the bearing caps. The bearing caps are bored while bolted onto their mating surface (either block saddle or connecting rod). If the caps were interchanged or reversed at a previous assembly, the bearings may show abnormal wear. Usually indicated by heavy wear on one side of the bearing. In other words, more wear occurs near one mating face because the upper half of the bore and the lower half do not "line up".

Illustration 49	g03477958
This connecting rod has the bearing cap reversed. This causes decreased oil clearances near the mating surfaces.

Illustration 50	g03477961
Irregular bearing wear due to reversed bearing caps. The arrows indicate heavy wear.

Corrective Measures to Address Irregular Wear

If the bearings indicate that there is a profile problem on the crankshaft journals, connecting rod or main rod bore diameter / shape, or misalignment of the main bores, follow the appropriate Reuse and Salvage Guideline to measure and repair the components. Check for proper surface finish of journals or bores, size, and shape of the journal or of the bores. Ensuring the mating components meet specification is necessary to have a bearing system that performs successfully.

Bearing Damage Caused by Debris

Bearings damaged by debris will have either scratches or embedded debris on the running surface. When the debris is severe, the damage can look like scuffing or smearing damage caused by lack of lubrication.

Debris or foreign particles cause approximately 50% of all bearing failures. This debris can take several forms, dirt (silicon), aluminum, steel, or grinder grit. It is important to realize that most of this debris can be eliminated by correct maintenance of the lubrication system and proper service practices.

During normal operation of the engine the oil filter removes debris from the system. If the filter plugs because of an excessive amount of debris or because of poor maintenance the oil bypasses the filter. During some cold starts the oil may also bypass the filter.

Debris particles damage a bearing in two ways. First, the particles can be carried between the journal and bearing thus causing scratching (scoring) of the bearing surface. Second, the particles can also become embedded in the bearing material. The amount of damage to the bearing surface depends on the size and concentration of the debris particles.

In small amounts and for small particle size, the bearings are designed to embed debris and then 'heal over' to be able to continue normal operation. However, if there is a large concentration of particles or large particles in the bearing system that have caused deep scratches or scoring of the surface of the bearing then the oil film between the bearing and the journal will be disrupted. These disruptions can result in an extreme amount of heat due to the increase in friction, and a bearing seizure (failure) can occur.

Remember, it is sometimes possible to discover bearing damage caused by debris at its early stages, before a complete failure occurs. This early discovery is possible if :

• The oil filter element is checked for debris at each oil change

• Scheduled Oil Sampling (S.O.S.) is used to monitor the condition of the lubrication system

Possible Sources of Debris

• Debris can be generated within an engine during operation. Example: Parts that wear excessively or parts that fail

• Debris may have been left in engine components during initial assembly or during a previous overhaul if parts and oil passages were not cleaned correctly.

• When an engine is removed from a vehicle, dirt can enter the disconnected lines that are left with the vehicle.

• Dirt can be added during an oil change. Remember to keep oil fill equipment clean.

• Dirt can enter through the air induction system. This dirt results from air leaks or poor maintenance to the air induction system

Examples of Debris Damage

Illustrations 51 through 55 are of individual bearings so the type of debris damage on the bearing can be seen more easily. However, when analyzing bearings that are damaged by debris always look at the complete set of main and rod bearings. Determine the oil flow. Which main bearing fed each rod bearing? Do the bearings indicate that the rod bearings were damaged only by bearing material that came from the failed main bearings or is there evidence that there was other debris in the lubrication system? For additional information see the topic "Engine Lubrication Systems" section of this guide.

Illustration 51	g03478090
This main bearing shows minimal debris wear caused by small particles of debris.

Illustration 52	g03478317
This main bearing show moderate debris wear caused by larger particles.

Illustration 53	g03478342
This main bearing shows heavy debris wear due to large particles.

Illustration 54	g03478358
Bearing damaged caused by embedded aluminum.

Illustration 55	g03478407
Bearing damage due to hard debris.

Debris sometimes becomes embedded in the bearing material. When soft material, such as aluminum, is embedded, it usually is flattened out on the bearing surface and then polished by the rotating journal as shown in Illustration 54. Hard debris usually causes raised material around the particle. This raised material is then polished. Therefore, when hard debris is embedded, it usually leaves a small spot where the debris entered. This spot is surrounded by a polished area as shown in Illustration 55.

Illustration 56	g03478416
Debris scratching shown on left. Gouges caused by pulled material on the right.

Bearings with an extreme debris failure can appear similar to a smeared bearing (caused by lack of lubrication). If the oil film is disrupted by debris, the journal may contact the bearing allowing some bearing material to seize or weld itself to the journal. This material is then pulled from the bearing by the rotating journal. The result is a gouge in the bearing surface.

Illustration 56 shows two bearings that are damaged by debris. One shows a bearing with debris scratches. The other bearing is starting to develop heavier debris damage. There are gouges caused by "pulled material". If debris continues to disrupt the oil film, the bearing damage will progress until the surface looks like a seized bearing. Such a case of a damaged bearing with smeared bearing material is likely to seize if operation continues for longer periods of time.

Illustration 57	g03478616

Illustration 58	g03478638

A bearing that is severely damaged by debris may give indications of some displacement of the bearing material. See Illustration 57. However, in most instances a debris-related failure can still be identified by the scratches that are visible near the mating face. See Illustration 58.

Corrective Measures for Debris Damage

• Recondition or replace other parts that were damaged by the debris (camshaft bearings, pistons, etc.)

• Maintain a clean work area. Concentrate on cleanliness during the overhaul. When an engine is removed from a vehicle, plug all disconnected lines to prevent dirt entry

• Clean all oil passages, including the block, crankshaft, oil pump, bypass valve and filter housings, external oil lines and auxiliary equipment. Remember to clean external oil lines including those remaining in a vehicle when the engine is removed. During initial operation, debris that is left in an engine can flow to the bearings before going through the lubrication system to the filter

• Oil coolers cannot be cleaned to remove debris. Oil coolers must be replaced

• Make certain that a new oil filter is installed. Also, install a new auxiliary filter, if the engine is so equipped

• Inspect the air induction system and make any repairs necessary

• Encourage the engine user to maintain correct oil and filter change intervals

• Encourage the engine user to monitor engine condition by using S.O.S. and oil filter examination

Bearing Damage Caused By Lack Of Lubrication

The term "lack of lubrication" refers to an insufficient oil film between the crankshaft journal and bearing. Lack of lubrication can be caused by low oil supply pressure, low oil level, wrong oil viscosity, and other conditions that result in deterioration of the oil film. The observation of lack of lubrication damage can occur due to a short period of no oil flow to the bearing (traditional 'lack of lubrication' condition), a prolonged period of operation with less than adequate oil flow to the bearings (called 'marginal lubrication') or adequate flow of oil with properties of the oil that are not correct. In each case, the observations of damage on the bearings are similar.

The first stage of lack of lubrication damage is smearing. A smeared bearing will have some displacement of the lead-tin overlay. Usually this displacement occurs in the center of the bearing, and there will be a buildup of overlay material at the end of the smear. The material buildup at the end of the smear is a characteristic signature of a lack of lubrication smear damage.

Illustration 59	g03478659
Smeared Bearing

A smeared bearing as shown in Illustration 59 progresses quickly to a scuffed bearing if the oil film is not restored. A scuffed bearing shows additional displacement of bearing material, including some of the alloy layer (aluminum based or copper based) as shown in Illustration 60. The displacement takes place when the extreme heat caused by friction melts the bearing materials, allowing displacement. The heat may also cause some bearing material to adhere or weld itself to the crankshaft journal, thus being pulled from the bearing as shown in Illustration 61. As journal rotation continues, this pulled material may be deposited back on the bearing along with the other displaced material.

Illustration 60	g03478856
Scuffed bearing

Illustration 61	g03479392
Pulled Material

A seized bearing is the final stage in the progression of damage caused by an insufficient oil film. When a bearing first starts to seize, it is similar to a scuffed bearing because it has the displacement of the alloy layers and pulled material. This damage usually progresses rapidly to a seized bearing, a bearing that has welded itself to the crankshaft journal and may have spun in the bore.

Illustration 62	g03479401

As was mentioned in the topic "Bearing Damage Caused by Debris" section, a scuffed bearing and a bearing with severe debris damage can look similar. This similarity is the result of "pulled material" that occurs when heavy debris damage disrupts the oil film. However, debris damage can still be recognized by the debris scratches near the mating face. Another important point is that a lack of lubrication failure can sometimes be identified because the bearings in the set will have all stages of lack of lubrication. See Illustration 62.

Possible Causes of Lack of Lubrication

• Low oil pressure as a result of: Oil pressure regulator malfunction, wear, or damage, component wear resulting in high oil flow through engine, external engine oil leak, and lubrication system issue.

• Low oil level as a result of: excessive oil consumption, excessive oil leakage, or failure of oil lines and insufficient oil in an engine (sometimes caused by ignoring auxiliary capacity).

• Wrong oil viscosity at a particular ambient temperature. (Oil that is too thick at colder temperatures, or oil that is too thin at warmer ambient temperatures)

• Contamination of the oil by fuel or coolant.

• Damaged, worn, or malfunctioning components in the lubrication system. Examples include: a plugged or damaged oil filter, failed oil lines or lines installed incorrectly, damaged or loose suction tube, belt, or screen, malfunctioning oil pump and worn or stuck valves in the lubrication system (by-pass valve for oil pump or oil cooler, lubrication valves).

Corrective Measures for Lack of Lubrication

• Encourage the engine user to perform correct lubrication system maintenance, including: use of the recommended oil, recommended oil and filter change intervals, regular monitoring of the engine oil level and inspection and repair of oil leaks

• If fuel or coolant contamination of the oil is suspected, an oil analysis can be used to confirm or disprove your suspicions.

• Check to see if the oil filters are plugged. Check the auxiliary filter if the engine is equipped with one.

• Make sure that the valves in the lubrication system are operating smoothly and are not damaged.

• When bearing damage caused by a lack of lubrication is severe, the following steps are necessary to remove the bearing material from the lubrication system: clean oil passages in the block, crankshaft, external oil lines, and auxiliary equipment, make sure that new oil and auxiliary filters is installed and install a new oil cooler. Oil coolers cannot be cleaned to remove debris or foreign material.

Cavitation Erosion

Cavitation erosion occurs in a bearing oil film during engine operation when the oil film pressure rapidly decreases causing tiny vapor bubbles to form. The bubbles later collapse as the pressure quickly increases. As the tiny bubbles collapse, a "jet" of fluid shoots past the bubbles and hits the bearing surface. This action is repeated many times, and erosion of the bearing surface results.

Some degree of cavitation erosion is usual in engine bearings. Observation of cavitation erosion is not uncommon on bearing surfaces. Cavitation erosion can manifest in the form of several shapes including round dots, crescent or kidney bean shapes, triangles, ovals, or small spots in a cluster.

Cavitation erosion will not normally cause a bearing failure because of: the time required to produce cavitation erosion is slow and the debris produced during cavitation erosion is microscopic.

There are instances of cavitation erosion that causes particles of the alloy layer to be plucked from the bearing and result in some debris damage or scratching of the bearing surface. However, this type of damage because the alloy layer is fairly soft and has a high degree of compatibility with the crankshaft rarely results in a bearing failure.

Because cavitation will not normally cause bearing failure, no corrective measures are necessary other than replacing the inspected bearings with new.

Illustration 63	g03479417
Typical location for cavitation erosion on a rod bearing.

Illustration 64	g03479478
Cavitation on a rod bearing with an oil groove.

Bearing "Hot Spots"

"Hot spots" are round wear areas on the running surface of the bearing that are caused by either debris or material buildup on the backside of the bearing between the bearing and the housing. The debris or material buildup results in a high spot on the bearing running surface and localized wear. A hot spot can disrupt the oil film enough to result in a bearing seizure if the high spot is large enough.

Material buildup on the backside of the bearing that results a hot spot can be caused by carbon deposits or by tin migration of the tin flash layer. Both carbon deposits or tin flash migration on the back of the bearing develop and increase in size over time, if they occur.

Causes of material buildup on the back of bearings can include:

• Insufficient bearing crush

• Main bearing block bores or connecting rod bores that are too large

• Parts were not installed correctly at the previous assembly

• Bolt torques that are not correct

• Oil quality (high soot levels)

If bearing hot spots are observed, ensure that the bore is thoroughly cleaned to remove the debris or deposit. Make sure that there is no damage in the bore due to debris and there is no dent on the bore surface. Correct any of the potential causes upon reassembly and further operation of the engine.

Illustration 65	g03479482
This bearing back has a mark on the back of the bearing caused by debris between the bearing bore and the bearing shell.

Illustration 66	g03479483
This bearing shows the hot spot caused by the debris on the back of the bearing shown in Illustration 66

Bearing Back Fretting

Fretting is the transfer of material from the back of the bearing to the bore. Fretting and shining of a bearing back takes place when the bearing crush is not sufficient, the bores are too large or the cap bolts are not tight. As a result, the bearing can move. Even though this movement is slight, the rapid motion of the bearing in the bore allows the bearing back to become shiny and/or fretted.

If fretting is observed, follow the corrective measures provided to address irregular wear patterns. The potential causes of fretting are the same as the potential causes of irregular wear, especially wrong bore diameter, and misassembly.

Illustration 67	g03479545
Bearing back has wear caused by fretting. Mating bearing cap shows transferred material.

Illustration 67 shows the back of a bearing that has suffered fretting.

Alloy Fatigue

Alloy fatigue is structural failure of the aluminum-based or copper-based alloy layer and results in gradual loss of the alloy layer material through a network of interconnected cracks. A fatigue failure sometimes occurs after the normal life of the bearing is exceeded. Fatigue failures can also be the result of excessive loads caused by debris damage, or uneven loading of the bearing.

A fatigue failure should not be confused with a bearing that has fatigue of the lead-tin overlay. The fatigue of the lead-tin overlay at low hours is a condition that may occur on some bearings that have thicker lead tin overlay. This type of fatigue is not harmful.

Corrective Measures for Alloy Fatigue

• Check the engine application. Make sure that the engine is not loaded excessively

• If the bearings are severely damaged, check the filters for debris. If there is debris in the system, the oil passages must be cleaned the same as with debris damage

Illustration 68	g03479578
Fatigue failure caused when normal life of bearing was exceeded.

Illustration 69	g03479591
Bearing that has fatigue of lead-tin overlay, which is not the same as a fatigue failure.

Bond Separation

Bond separation is the removal of one or more material layers from the bearing during operation and can occur for several reasons, either because of a poor bond between the bearing layers or debris damage at assembly or during operation. Extreme heat can result when debris scratches the bearing surface during operation or when the journal contacts the bearing, and the heat will weaken the bond of the layers to the point of failure. If debris were pressed into the bearing at assembly (rather than scratching during operation), a divet on the alloy surface can be created that acts as a stress concentrator. The stress concentrator will increase the bearing layer stress above the strength level, and the bond will fail.

Bond separation is different than alloy fatigue in that for bond separation a single area of bearing material has been removed and with alloy fatigue the material is removed in interconnected cracks.

A bond separation can occur either between the lead- tin overlay and alloy layer or between the alloy layer and the steel back.

When the lead-tin overlay separates from the alloy, a poor bond is usually the cause. However, separation of the aluminum from the steel back can be caused by a poor bond, from extreme heat, or debris damage at assembly.

When engine bearings give indications of a bond separation, evaluate all bearings from the set for evidence of another failure. If all bearings have damage caused by debris or lack of lubrication the bond failure was probably secondary, resulting from the heat. Remember, a bond failure allows small pieces of bearing material to come off the bearing. When a bond failure occurs on a main bearing, the bearing material may flow to one or two rod bearings causing damage.

Corrective Measures for Bond Separation

The corrective measures for a bond failure will vary depending on the severity of the damage. If one bearing has a bond failure that allows a small amount of aluminum or copper-based material in the system, the problem is not as severe. Replacement of that damaged bearing is probably sufficient.

If a bond failure occurs on more than one bearing, or if the bond failure causes failure of other bearings, more corrective measures are needed. When the damage is severe, do the following:

• Determine if other damage caused the bond separation (lack of lubrication, debris). Take corrective action as necessary.

• Clean all oil passages in the block, crankshaft, and auxiliary equipment

• Make certain that a new oil filter is installed. Also, install a new auxiliary filter if the engine is so equipped

• Install a new oil cooler. Oil coolers cannot be cleaned to remove debris or bearing material

Illustration 70	g03479600
Bond separation between the lead-tin overlay and aluminum.

Illustration 71	g03479601
Bond separation between aluminum and steel.

Electrical Discharge Damage

Note: This type of damaged is unusual, and is most often limited to engines in generator sets but also has occurred on engines with large alternators.

Electrical Discharge Damage is when electrical current goes through the crankshaft, bearings, and into the block due to poor grounding. When the electrical current goes through the engine, an arc occurs between the bearing and the crankshaft and block. This arcing causes damage on only the main bearing. Electrical Discharge damage makes the main bearings shiny and causes significant damage. Electrical Discharge also creates a frosted appearance on the crankshaft journals from pitting from arcing current.

Illustration 72	g03480144
Main bearings that have been damaged by electrical discharge. Note the "chrome like" bearing surface

Illustration 73	g03480158
A crankshaft journal that has been damaged by electrical discharge. Note the "frosted" appearance on the journal.

Illustration 74	g03480160
A bearing back damaged by electrical discharge. Note the unusual wear pattern caused by arcing current.

Bearing Failure Analysis

Bearing failure analysis is not always simple. Many times the cause of a failure cannot be determined by looking at the bearings alone. More information, such as engine repair history or information from the operator may be needed. Also, mating parts must sometimes be inspected to determine involvement in the failure. Frequently, a bearing set will show evidence of more than one failure cause. Bearings may be destroyed during a failure, thus removing the evidence shown by the present attributes.

Procedure for Analyzing Bearing Failures

If a bearing failure is suspected in an engine, it is important to perform the correct failure analysis steps in the correct sequence. The following recommendations will help you to be more successful in analyzing failures.

• Get operating information from the operator: How was the engine being operated at the time of failure? What was the engine coolant temperature before and during the failure? Did oil pressure change before or during failure? What were the symptoms during the failure?

• Get maintenance information: What were the oil change intervals? When was the oil last changed? What oil was used? What was the classification and viscosity? If equipped with an auxiliary filter, when was the filter last changed?

• Obtain the history of engine repairs: Is there data available from a previous oil analysis? Was there a recent overhaul or repair?

• Perform an external inspection of the engine: Check and record the oil level. Are there any apparent oil leaks or loose oil line connections? Are there any new oil lines? Are the lines installed correctly?

• Remove and cut open the oil filters for inspection: Is the filter element plugged? Is there any debris in the element? Is the filter ruptured (or split)?

Note: When a bearing failure occurs, bearing material will usually flow to the filter. If there is no bearing material or debris in the filter, the engine probably did not have a bearing failure. It is important also to remember that if there was no oil flow during the failure, then the bearing material from the failure would not flow to the filter. If necessary, install a new filter and operate the engine to detect the problem (such as damaged timing gears or fuel nozzle knock).

• If, after the above steps are performed, a bearing failure is still suspected, drain the oil from the pan. As the oil is drained, use a Scheduled Oil Sampling bottle to collect a sample of the oil. This oil sample can later be analyzed, if necessary, to determine if there is coolant, fuel, or debris in the oil.

• Remove the oil pan: Is there debris in the oil pan? If so, what debris (ferrous, non-ferrous, etc.)? Check the rod and main bearing caps for heat discoloration and looseness.

• Remove the main and connecting rod bearings. Mark the bearings with the location in the engine as removed. Match the upper and lower bearing halves with their locating tabs together. Tape the bearings together in groups of uppers and lowers.

• Visually inspect the bearings to determine the failure cause. Look at the entire set. Which main bearing fed oil to each rod bearing?

• If still necessary, perform further investigation: Examine and measure the mating parts. Inspect the lubrication system components for condition and correct operation (pump, bypass valves, etc.).

Illustration 75	g03479637
Oil filter element after a major bearing failure.