Reusability of Drive Train Gears {3002, 3159, 3256, 4055} Caterpillar

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Introduction

Table 1

Revision	Summary of Changes in SEBF8193
21	Added new serial number prefixes for New Product Introduction (NPI). Updated copyright date to 2018. Removed Repair Process Engineering (RPE) old point of contacts. New Repair Process Engineering (RPE) point of contact added.
20	Added extra photos.
19	Added extra photos.
18	Added Expanded Mining Products and extra photos.

© 2018 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 Cat 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 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, 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. Cat dealers can supply the most current information.

Note: ALL ILLUSTRATION DESCRIPTIONS CAN BE FOUND JUST BELOW ILLUSTRATIONS.

Summary

This guideline contains information which can help to determine visually the reusability of gears in the drive train. This guideline also contains the operational characteristics of gears in the drive train. The information that is shown in this guideline will help to explain the cause and succession of a failure. Never install a part that is shown in this guideline as a part that cannot be used again. This guideline can help to identify the gears that may be used again by illustrating the typical modes of failure. This guideline cannot guarantee that any individual gear can be reused. There is always some risk of failure. Experience and careful inspection is the best guideline for proper usage of gears.

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

Use the following references for additional information regarding the rebuild of a drive train.

Table 2

References
SEBF8029	Reuse And Salvage Guidelines "Index of Repair Process Engineering Publications"
SEBF8148	Reuse And Salvage Guidelines "General Salvage and Reconditioning Techniques"
SEBF8185	Reuse And Salvage Guidelines "Salvage Procedure for Final Drive Planet Gear Used in Off-Highway Trucks"
SEBF8187	Reuse And Salvage Guidelines "Standardized Parts Marking Procedures"

Tooling and Equipment

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NOTICE
Failure to follow the recommended procedure or the specified tooling that is required for the procedure could result in damage to components. To avoid component damage, follow the recommended procedure using the recommended tools.

Table 3 contains the items that are needed to complete the repair procedures in this guideline.

Table 3

Tooling and Equipment
Part Number	Description
1U-9918	Wire Brush
1P-3537	Dial Bore Gauge Kit
4C-4804	Penetrant
4C-4805	Developer
5P-1720	Seal Pick
6V-2010	Polishing Stone
8S-2257	Eye Loupe
8T-7765	Surface Reconditioning Pad
8T-9290 or 146-1738	Borescope Inspection Kit
9A-1593	Surface Texture Comparison Gauge
9U-7377	Metal Marking Pen
170-5903	Gear Inspection Stand
238-8244	White LED Pen Light
262-8390	Microscope
263-7184	Crack Detection Kit
269-3123	Blue LED Pen Light
288-4209	Paper Towel
385-4008	Outside Micrometer Set 6–60 inch
385-9422	Inside Micrometer Set 2-24 inch
415-4055	Ultrasonic Tool Kit
420-5317	Tool Crib
448-0722	Borescope Probe (17 mm Side view Camera)
448-0723	Borescope Probe (5.5 mm HD Camera)
448-0724	Wired Video Borescope
448-0725	Wireless Video Borescope
459-0184	UV Light Kit
473-8688 or 473-8689	Inside Micrometer Set 2-12 inch
	Inside Micrometer Set 50-300 mm
474-3709 or 474-3710	Inside Micrometer Set 8-32 inch
	Inside Micrometer Set 200-800 mm
-	Reflective Surface for Inspection

Prepare the Area for Inspection

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Personal injury can result when using cleaner solvents. To help prevent personal injury, follow the instructions and warnings on the cleaner solvent container before using.

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Personal injury can result from air pressure. Personal injury can result without following proper procedure. When using pressure air, wear a protective face shield and protective clothing. Maximum air pressure at the nozzle must be less than 205 kPa (30 psi) for cleaning purposes.

• Clean all surfaces for inspection before you inspect the part. Make sure that you remove all debris, paint, and oil.

• When you move parts that require cleaning, always use a proper lifting device. This device must protect the part from damage. For the safety of the operator, all lifting devices must be inspected before use.

• During cleaning, do not damage machined surfaces.

• Use pressurized air to dry parts.

• If the bore cannot be inspected immediately after cleaning, put hydraulic oil on all machined surfaces to prevent rust or corrosion. Carefully store the parts in a clean container.

• Use appropriate thread taps to chase all threaded holes.

Standardized Parts Marking Procedure

Reference: Refer to Reuse And Salvage Guideline, SEBF8187, "Standardized Parts Marking Procedures" for additional information regarding marking procedures.

The code is a Caterpillar standard. The code is used to record the history of a gear. The code will identify the number of rebuilds and hours at the time of each rebuild. This information is important for any decision to reuse a gear. The information should be considered for making an informed decision to reuse a gear. The information should be considered for locating the cause of a failure.

The mark should be on the sides of planetary gears and sun gears. The mark is not to be covered by a mating part. Use 9U-7377 Metal Marking Pen that is listed in "Tooling and Equipment" to mark the code onto the gear.

The procedure for marking gears is a Caterpillar standard. This code is helpful when the machine is sold into a different territory after the first rebuild. During an overhaul, the previous code of a part should never be removed.

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NOTICE
Do not use a numbering stamp punches set to mark internal parts. The impact from striking the stamp will cause an abnormal stress riser. The added stress riser may cause the part to fail prematurely.

Example 1

Illustration 3	g03885120

Illustration 3 shows code (1-15). The first number (1) indicates that the component had been rebuilt once. The second number (15) indicates that there were 15,000 hours on the gear at the time of rebuild.

Example 2

Illustration 4	g03885129

Illustration 4 shows code (1-12) and code (2-10). Code (2-10) represents the information from the second rebuild. The first number (2) indicates that the component had been rebuilt twice. The second number (10) indicates that there were 10,000 hours on the gear at the time of rebuild.

Note: To obtain the total number of hours for the component in Illustration 4, add first and second rebuild hours. In this example the component has a total of 22,000 hours.

Crack Detection Methods

Crack detection methods or Non-Destructive Testing (NDT) are utilized for examining components for cracks without damaging the component. Visual inspection, Liquid Penetrant Testing (PT), Magnetic Particle Inspection (MPI), Ultrasonic Testing (UT), Radiographic Testing and Eddy Current Testing are recommended methods. There may be more than one acceptable crack detection method for the inspection of a given part, though the liquid penetrant is the most versatile. For example, the liquid penetrant method can be used when inspecting smooth machined components such as shafts, gear teeth, and splines. Use of the Wet Magnetic Particle Inspection is more accurate than the use of the liquid penetrant method. Refer to Table 4 for advantages and disadvantages and Table 5 for standards and requirements for these NDT methods.

Table 4

Crack Inspection Method Advantages vs. Disadvantages
Inspection Method	Advantages	Disadvantages
Visual Surface Inspection (VT)	- Least expensive - Detects most damaging defects - Immediate results - Minimum part preparation	- Limited to surface-only defects - Requires inspectors to have broad knowledge of welding and fabrication in addition to NDT
Liquid Penetrant (PT)	- Inexpensive - Minimal training - Portable - Works on nonmagnetic material	- Least sensitive - Detects surface cracks only - Rough or porous surfaces interfere with test
Dry Magnetic Particle (MPT)	- Portable - Fast/Immediate Results - Detects surface and subsurface discontinuities	- Works on magnetic material only - Less sensitive than Wet Magnetic Particle
Wet Magnetic Particle (MPT)	- More sensitive than Liquid Penetrant - Detects subsurface as much as 0.13 mm (0.005 inch)	- Requires Power for Light - Works on magnetic parts only - Liquid composition and agitation must be monitored
Ultrasonic Testing (UT)	- Most sensitive - Detects deep material defects - Immediate results - Wide range of materials and thickness can be inspected	- Most expensive - Requires operator training and certification - Surface must be accessible to probe
Eddy Current Testing (ET)	- Surface and near surface flaws detectable -Moderate speed/Immediate results -Sensitive too small discontinuities	- Difficult to interpret - Only for metals -Rough surfaces interfere with test - Surface must be accessible to probe
Radiographic Testing (RT)	-Detects surface and internal flaws - Minimum part preparation - Can inspect hidden areas	- Not for porous materials - Radiation protection needed - Defect able to be detected is limited to 2% of thickness

Table 5

Applicable Crack Detection Standards
Type	Standard	Acceptance Criteria	Required Personnel Qualifications
Visual Surface Inspection (VT)	EN-ISO 5817 AWS D1.1	EN-ISO 5817 - Level B AWS D1.1 - Table 6.1	EN-ISO 9712 - Level 2 ANSI-ASNT SNT-TC-1A Level 2
Liquid Penetrant Testing (PT)	EN-ISO 3452 ASTM E165	EN-ISO 23277 AWS - D1.1	EN-ISO 9712 - Level 2 ANSI-ASNT SNT-TC-1A Level 2
Magnetic Particle Testing (MPT)	EN-ISO 17638 ASTM E709	EN-ISO 23278 - Level 1 AWS D1.1 - Table 6.1	EN-ISO 9712 - Level 2 ANSI-ASNT SNT-TC-1A Level 2
Ultrasonic Testing (UT)	EN-ISO 17640 - Level B AWS D1.1	EN-ISO 11666 Technique 2 - Level 2 AWS D1.1 - Class A - Table 6.3	EN-ISO 9712 - Level 2 ANSI-ASNT SNT-TC-1A Level 2
Eddy Current Testing (ET)	EN-ISO 15549 ASTM E426	EN-ISO 20807	EN-ISO 9712 - Level 2 ANSI-ASNT SNT-TC-1A Level 2
Radiographic Testing (RT)	EN-ISO 5579 ASTM E94	EN-ISO 10657-1	EN-ISO 9712 - Level 2 ANSI-ASNT SNT-TC-1A Level 2

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NOTICE
Regardless of which crack detection method is used, it is important that the instructions furnished with the detection equipment are followed closely when checking any component. Failure to do so may cause inaccurate results or may cause injury to the operator and/or surroundings.

Visual Surface Inspection (VT)

Illustration 5	g06085008
Example of Visual Inspection Tools (A) Flashlight or adequate light source (B) Magnifying eye loupe (C) Tape measure or other measuring device (D) Inspection mirror (E) Weld size inspection gauges

Components and welds that are to be inspected using PT, MPT, or UT shall first be subject to visual inspection (VT). Visual Inspection is often the most cost-effective inspection method and requires little equipment as seen in Illustration 5. It is suggested that at a minimum personnel performing Visual Inspection are either trained to a company standard or have sufficient experience and knowledge about the components being inspected. It is also suggested that personnel performing visual inspections take some type of eyesight test regularly.

Liquid Penetrant Testing (PT)

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Personal injury can result from improper handling of chemicals. Make sure you use all the necessary protective equipment required to do the job. Make sure that you read and understand all directions and hazards described on the labels and material safety data sheet of any chemical that is used. Observe all safety precautions recommended by the chemical manufacturer for handling, storage, and disposal of chemicals.

Materials and Equipment Required

Refer to Tooling and Equipment Table 3 for part numbers.

• Cleaner: Removes dirt before dye application and dissolves the penetrant making possible to wipe the surface clean.

• Penetrant: This solution is highly visible, and will seep into openings at the surface of a part with capillary action.

• Developer: Provides a blotting action, bringing the penetrant out of the discontinuities and providing a contrasting background to increase the visibility of the penetrant indications.

• Wire Brush: Removes dirt and paint.

• Cloth or Wipes: Use with cleaner and for other miscellaneous uses.

Procedure

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Illustration 6	g06087907
Typical example of checking for cracks in the welded areas.

1. Preclean inspection area. Spray on cleaner / remover to loosen any scale, dirt, or any oil. Wipe the area to inspect with a solvent dampened cloth to remove remaining dirt and allow the area to dry. If, there is a visible crack remove paint using paint remover or wire brush.
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   Illustration 7	g06087912
   Typical example of checking for cracks in the welded areas.

2. Apply penetrant by spraying to the entire area to be examined. Allow 10 to 15 minutes for penetrant to soak. After the penetrant has been allowed to soak, remove the excess penetrant with clean, dry wipe.
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   Illustration 8	g06087914

3. The last traces of penetrant should be removed with the cleaner solvent dampened cloth or wipe. Allow the area to dry thoroughly.
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   Illustration 9	g06087916

4. Before using Developer, ensure that the developer is mixed thoroughly by shaking can. Hold thecan approximately 8-12 inches away from part, apply an even, thin layer of developer over the area being inspected. A few thin layers are a better application method than one thick layer.
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   Illustration 10	g06084042
   Typical example of cracks found during a liquid penetrant examination.

5. Allow the developer to dry completely for 10–15 minutes before inspecting for cracks. Defects will show as red lines in white developer background, refer to Illustration 10. Clean the area of application of the developer with solvent cleaner.

Dry Magnetic Particle Testing (MPT)

Materials and Equipment Required

Refer to Tooling and Equipment Table 3 for part numbers.

Illustration 11	g06085930
(A) Indications shown by magnetic particle testing. (B) Typical electromagnetic yoke. (C) Dry powder bulb.

1. Dry magnetic powder shall be of high permeability and low retentively and of suitable sizes and shapes to produce magnetic particle indications. The powder shall be of a color that will provide adequate contrast with the background of the surface being inspected.

2. Dry magnetic particles shall be stored in suitable containers to resist contamination such as moisture, grease, oil, non-magnetic particles such as sand, and excessive heat. Contaminants will manifest in the form of particle color change and particle agglomeration. The degree of contamination will determine further use of the powder.

3. Dry magnetic powder shall be tested in accordance with ASTM E709 Section 18 (Evaluation of System Performance/Sensitivity) when not performing.

4. Equipment should include a "U" shaped electromagnetic yoke made from highly permeable magnetic material, which has a coil wound around the yoke. This coil carries a magnetizing current to impose a localized longitudinal magnetic field into the part. The magnetizing force of the yoke is related to the electromagnetic strength and can be tested by determining the lifting power of a steel plate. The yoke shall have a lifting force of at least 4.5 kg (10 lbs).

5. Check dry powder blower routinely to ensure that the spray is a light, uniform, dust-like coating of the dry magnetic particles. Blower should also have sufficient force to remove excess particles without disturbing those particles that are evidence of indications.

6. All equipment shall be inspected at a minimum of once a year or when accuracy is questionable.

Procedure

1. Ensure surface to be inspected is dry and free from oil, grease, sand, loose rust, mil scale, paint, and other contaminants.

2. Apply the magnetic field using the yoke against the faces and inside diameter of each bore.

3. Simultaneously apply the dry powder using the dry powder blower.

4. Remove excess powder by lightly blowing away the dry particles.

5. Continue around the entire circumference of each bore. Position the yoke twice in each area at 1.57 rad (90°) to ensure that multiple directions of the magnetic field are created.

6. Observe particles and note if any clusters of particles appear revealing an indication.

7. Record the size and shape of any discontinuities or indications found.

Wet Magnetic Particle Testing (MPT)

Materials and Equipment

Refer to Tooling and Equipment Table 3 for part numbers.

Illustration 12	g06085937
(A) Indications shown by magnetic particle testing. (B) Typical electromagnetic yoke. (D) UV Lamp used in wet magnetic particle inspection process.

Illustration 13	g06003178
Pear Shaped Centrifuge Tube

1. Wet magnetic particles are fluorescent and are suspended in a vehicle in a given concentration that will allow application to the test surface by spraying.

2. Concentration:

   1. The concentration of the suspended magnetic particles shall be as specified by the manufacturer and be checked by settling volume measurements.

   2. Concentrations are determined by measuring the settling volume by using an ASTM pear shaped centrifuge tube with a 1 mL (0.034 oz) stem with 0.05 mL (0.0017 oz) 1.0 mL (0.034 oz) divisions, refer to Illustration 13. Before sampling, the suspension shall be thoroughly mixed to assure suspension of all particles, which could have settled. A 100 mL (3.40 oz) sample of the suspension shall be taken and allowed to settle for 30 minutes. The settling volume should be between 0.1 mL (0.0034 oz) and 0.25 mL (0.0085 oz) in a 100 mL (3.40 oz) sample.

   3. Wet magnetic particles may be suspended in a low viscosity oil or conditioned water.

   4. The oil shall have the following characteristics:

      • Low viscosity not to exceed 50 mSt (5.0 cSt) at any temperature at which the vehicle is to be used.

      • Low inherent fluorescence and be non-reactive.

   5. The conditioning agents used in the conditioned water shall have the following characteristics:

      • Impart good wetting characteristics and good dispersion.

      • Minimize foaming and be non-corrosive.

      • Low viscosity shall not exceed a maximum viscosity of 50 mSt (5.0 cSt) at 38° C (100° F).

      • Non-fluorescent, non-reactive, and odorless.

      • Alkalinity shall not exceed a pH of 10.5.

3. Equipment should include a "U" shaped electromagnetic yoke made from highly permeable magnetic material, which has a coil wound around the yoke. This coil carries a magnetizing current to impose a localized longitudinal magnetic field into the part. The magnetizing force of the yoke is related to the electromagnetic strength and can be tested by determining the lifting power of a steel plate. The yoke shall have a lifting force of at least 4.5 kg (10 lbs).

Procedure

1. Ensure surface to be inspected is dry and free from oil, grease, sand, loose rust, mil scale, paint, and any other contaminants.

2. Apply the magnetic field using the yoke against the surface in the area to be inspected.
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   Illustration 14	g03536210

3. For case hardened and ground surfaces:

   • Due to the sensitivity required to locate the grinding cracks, inspection of case hardened and ground surfaces require that the yoke is applied so that the magnetic field is 1.57 rad (90°) to the expected direction of the indications. Also, due to the increased sensitivity resulting when the yoke is energized, the yoke is not moved until the evaluation is completed in the first direction. An AC yoke shall be used. See Illustration 14 for an example of yoke placement.

4. Visually inspect for indications of discontinuities using the proper illumination.

5. Record the size and shape of any discontinuities found.

Ultrasonic Testing (UT)

Refer to Tooling and Equipment Table 3 for part numbers.

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NOTICE
All personnel involved in ultrasonic examinations shall be qualified to Level 2 in accordance to standards stated in Table 5.

1. Ultrasonic testing (UT) is a method of Non-Destructive Testing (NDT) using short ultrasonic pulse waves (with frequencies from 0.1-15 MHz up to 50 MHz) to detect the thickness of the object. Ultrasonic testing consists of an ultrasound transducer connected to a diagnostic machine and passed over the object being inspected.

2. There are two methods of receiving the ultrasound waveform from the transducer: reflection and attenuation.

   a. Reflection - Ultrasonic pulses exit the transducer and travel throughout the thickness of the material. When the sound waves propagate into an object being tested, the waves return to the transducer when a discontinuity is discovered along the sonic path. These waves continue and reflect from the back surface of the material to project the thickness of the material.

   b. Attenuation - A transmitter sends ultrasound through one surface, and a separate receiver detects the amount that has reached it on another surface after traveling through the medium. Any discontinuities or other conditions within the medium will reduce the amount of sound transmitted, revealing the presence of the imperfections.

Eddy Current Testing

Illustration 15	g06090873
Eddy-current testing

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NOTICE
All personnel involved in Eddy Current examinations shall be qualified to Level 2 in accordance to standards stated in Table 5.

Eddy-current testing (ET) is a Non-Destructive Testing (NDT) method in which eddy-current flow is induced in the test object. Changes in the flow caused by variations in the specimen are reflected in to a nearby coil or coils for subsequent analysis by suitable instrumentation and techniques. Major applications of eddy-current testing are surface inspection and tubing inspections.

Radiographic Testing

Illustration 16	g06090892
Radiographic Testing

All personnel involved in radiographic examinations shall be qualified to Level 2 in accordance to standards stated in Table 5.

Illustration 17	g00008666

This process is dangerous. Only qualified personnel and test equipment should be appointed to perform this type of testing.

Radiographic testing (RT) is a Non-Destructive Testing (NDT) method in which short wavelength of electromagnetic radiation is used to penetrate materials to find hidden discontinuities such as cracks. In radiographic testing, the test object is placed between the radiation source and the film, or x-ray detector. The electromagnetic radiation will penetrate the thickness of the test object and, when all the way through, will project onto the film any indications that have been in the path of the radiation waves.

Nomenclature of Gears

Illustration 18	g03885136
Key elements of a gear are identified in Table 6.

Table 6

Nomenclature of Gear Teeth
Item	Description
1	End
2	Tip
3	Land of tip
4	Edge
5	Face of tooth
6	Highest point of single tooth contact (HPSTC)
7	Pitch Line
8	Lowest point of single tooth contact (LPSTC)
9	Fillet
10	Root
11	Start of active profile
12	Crown
13	Profile
14	Pitch diameter of gear
15	Thrust face

Glossary of Terms

Profile - The profile of the gear teeth is the shape or the outline of the gear tooth from the side of the gear.

Addendum - The addendum is the section of tooth that is above the pitch line.

Pitch Line - The pitch line is located between the highest point of single tooth contact (HPSTC) and the lowest point of single tooth contact (LPSTC). Sliding between the surfaces of gear teeth does not occur at the pitch line.

Crown - The crown of a gear tooth is the outline that can be seen from the top of the tooth. The crown is shown as item (12) in Illustration 18. The roundness of the crown of a tooth compensates for a minor misalignment between the teeth of a gear. The crown can also help distribute the load from the center of the tooth outward for more efficiency.

Dedendum - The Dedendum is the section of the gear tooth that is below the pitch line.

DO NOT USE THIS PART AGAIN - The DO NOT USE THIS PART AGAIN refers to a part that is either out of specifications or is damaged upon repair and is not to be used again.

USE THIS PART AGAIN - The USE THIS PART AGAIN refers to a part that after accurate inspection and reconditioning, has meet the criteria and can be used again.

BORDERLINE - BORDERLINE refers to a part that depending on the application, operation, maintenance, and serviceability should be considered reusable or not. Use proper inspection procedures to verify.

Gear Types

Illustration 19	g03885141
Spur Gears Spur gears have parallel shafts. The load is applied to one single tooth. The load is applied to 1/3 of the adjacent tooth.

Illustration 20	g03885145
Helical Gears Helical gears have either parallel shafts or perpendicular shafts. Helical gears are quiet. Multiple teeth carry the load.

Illustration 21	g03885152
Straight Bevel Gears Straight bevel gears have either angled shafts or perpendicular shafts. Approximately 1 and 1/3 teeth carry the load. Some end thrust is produced.

Illustration 22	g03885159
Spiral Gear Hypoid pinions or spiral gear shafts are perpendicular to each other. The gear teeth are curved to provide more contact area between mating teeth. The design creates quiet operation with more sliding tooth contact, and end thrust. Two or more teeth carry the load.

Case Hardened Surface

All Caterpillar gears are heat-treated. Caterpillar Gears are designed by persons that select the proper material and heat treatment which enables Caterpillar gears to meet desired standards for performance, life, and durability. Most Caterpillar gears are case hardened to provide the gears with a hard, durable surface, and a strong, tough core.

There are several different case hardening heat treatments. The most typical treatments for Caterpillar gears are nitriding and carburizing. Nitriding provides a shallower hardened case typically from 0.13 mm (0.005 inch) to 0.3 mm (0.01 inch). Nitrided gears, which require higher dimensional accuracy, are loaded with lighter loads. Carburized gears are typically utilized in applications with the highest loads. The carburized gears are typically used in final drives. The depths of the case can vary from 0.5 mm (0.02 inch) to 2.0 mm (0.08 inch).

The proper selection of design, materials, and heat treatment produce gears that are capable of providing the best life and performance in the harshest applications.

Machine Application, Operation, and Maintenance

Consider the following information in all decisions to reuse gears:

• Machine application

• Machine operation

• Machine maintenance

Assume high hours, insufficient maintenance, and heavy applications if the history of the machine is not known. Decisions for reusing gears should never be based on one characteristic. Gears are designed to withstand the sliding action between the surfaces of mating teeth. Gears are not designed to withstand conditions of insufficient lubrication. Insufficient lubrication can cause direct contact between gears. Direct contact increases resistance and operating temperatures. Inadequate lubrication will cause serious damage if regular maintenance is ignored. These conditions will eventually contribute to abnormal wear or accelerated wear during operation.

Methods for Minimizing Gear Failures

1. Gear trains are easily contaminated during field assembly. Always use clean procedures. Clean procedures will always minimize the possibility for contamination.

2. Use only the recommended procedures for assembly. Proper levels of oil should be maintained. Only use Caterpillar recommended lubricants to minimize internally generated debris from wear.

3. Replace any breathers that are dirty to minimize airborne contamination.

4. Schedule a Scheduled Oil Service (SOS) that is certified by Caterpillar to find possible causes of oil contamination. An oil analysis can help determine the cause of a failure. An oil analysis can also help the prevention of possible future failures. Keep an accurate record of the machine hours and application. The information will be used during the oil analysis to generate the most accurate diagnosis.

5. The specified filters should be used and changed at the recommended intervals if gear oil passes through a system of filters.

6. Change the drive train oils at the recommended intervals. The intervals can be found in the Service Manual for the machine.

7. Be certain that all gears are free of rust and debris during a rebuild. Examine the gears to check for any damage from handling.
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   Illustration 23	g03880743
   Do not place gears on the floor or stack the gears on top of each other.

8. Gears should be handled carefully. Gears should be stored properly during rebuilding. Gears are easily chipped. A chipped tooth is shown in Illustration 24.

   1. Do not stack the gears or place the gears on the floor. Illustration 23 shows the improper way of stacking gears.

   2. Stack the gears in a stable pattern. Place the large gears on the bottom and the smaller gears toward the top. Use cardboard to separate the gears when gears are stacked.

   3. Use a nylon sling to lift a gear. Use of a nylon sling will help to prevent damage to the bore of the gear. Follow all Caterpillar safety standards for operating a hoist.

9. Record the history of the machine. Record the hours of usage for the component.
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   Illustration 24	g03885167
   Not properly handling a gear may cause the teeth to break. The gear in the above illustration was not handled properly.

10. Record the number of rebuilds and hours on all gears. Refer to "Standardized Parts Marking Procedure" for more information.

Operational Characteristics of Gears

The information in this section will explain the basic terminology and different operational characteristics of gears.

Caterpillar Genuine Gears

Caterpillar gears deliver maximum performance and productivity under extreme loads. The teeth of the gears move against each other. The teeth are under high stress to convert engine horsepower into torque. Caterpillar gears in drive trains are built with the purpose of transmitting extreme loads. The gears are built to work as a system with the following unique features:

• Smooth tooth surfaces

• Resistance to pitting and scoring

• Prevention of excess contact and stress on meshing teeth

• Geometry of teeth that is resistant to breaking

• Metallurgy of gears that is specific to applications

• Proprietary heat-treat processes

The properties of Caterpillar gears differentiate the gears from other replacement or remanufactured gears. Maximum machine performance and productivity can be ensured by installing genuine Caterpillar gears in your Caterpillar equipment. Caterpillar gear teeth are specially shaped to distribute stress over a large area. The shape of the gears prevents tooth fracture.

Competitive Gears

Competitive manufacturers of gears claim to produce gears that can be used in many different machines because the gears are designed for multiple pieces of equipment. Every Caterpillar gear has a specific design for each application. These acute yet important differences are critical to the life of any drive train. The use of Caterpillar gears will ensure correct gear tooth contact and efficient power flow under varying load conditions. Only Caterpillar genuine gears should be installed into Caterpillar equipment.

Metallurgy

Caterpillar gears have unique metallurgical compositions. The metallurgical content of each gear is tailored to the specific application of the gear. Caterpillar improves the impact resistance of the gears. Caterpillar also ensures the proper transfer of loads and consistency by utilizing special steel formulas.

Case Hardened Surface

Highly loaded gears in the drive train require a case hardened surface. All gears in the drive train are heat treated to a specified level of hardness. The depth of the case hardened surface depends on the size of the gear, the application of the gear, and the metallurgy of the gear. The Caterpillar patented heat treat process can offer extended gear life to highly loaded gears in drive trains. The smallest Caterpillar gears will usually be heat treated to a depth of at least 0.20 mm (0.008 inch). Large Caterpillar gears can be heat treated to a depth of 12.70 mm (0.500 inch).

Rolling Action and Sliding Action

The gear teeth go through a combined rolling and sliding action when gears rotate in and out of a mesh. Rolling and sliding occurs during contact above the pitch line and below the pitch line. Only rolling occurs at the pitch line.

Illustration 25	g03885179
The illustration shows the rolling and sliding action that occurs as a gear rotates. (14) Pitch diameter (16) Loaded side of tooth (17) Unloaded side of tooth (18) Rolling action (19) Rolling and sliding action

LPSTC and HPSTC

The LPSTC is low on the gear tooth. Pitting usually occurs at the LPSTC. The HPSTC is high on the gear tooth. Scoring usually occurs at the HPSTC and above the HPSTC.

Illustration 26	g03885181
LPSTC and HPSTC (6) HPSTC (8) LPSTC (20) Driven gear (21) Driving gear (22) Full tooth contact with rolling action

Load and Velocity of Contact

The load on gear teeth and the velocity of gear tooth contact relate to each other. Wear increases with increases in load. Scoring increases with increases in the velocity of contact.

Illustration 27	g03885185
Gears have maximum operating life in zone (24). The oil must be clean. Maximum life of the gear will occur under medium gear speeds. Maximum life of a gear will occur under lower loads on gears. The line of wear (23) will increase at a steeper angle if the oil is contaminated. Oil contamination will shift the complete graph toward the origin. (23) Wear (24) No wear with clean oil (25) Scoring (26) Pitting (27) Breakage (28) Velocity of contact (29) Load

Thickness of Lubrication

The thickness of the lubrication film is important. The temperature of the lubrication, the amount of the lubrication, and speed of the gear can affect the thickness of the lubrication. The thickness of lubrication can also affect the type of wear. Refer to Illustration 27 for the following combinations of the usage of gears.

Slow gear speed - A slow gear speed can allow the oil to leave the surface of the gear. Slow gear speeds can cause metal contact. At a slow gear speed, the gear teeth will have insufficient lubrication.

Fast gear speed - A fast gear speed can cause the teeth to penetrate the thin film of lubrication during operation. Gear speeds that are too fast usually result in metal tooth contact.

High loads on gears - A high load at a slow velocity of gear contact will have accelerated wear characteristics . High loads can penetrate a thin film of lubrication. A high load can break the film of lubrication at both slow gear speeds and fast gear speeds. Accelerated wear can happen at slow speeds. Breakage and pitting may happen at high gear speeds.

High velocity of gear contact - High velocities of gear contact will usually cause scoring. High velocities of contact with elevated loads will usually cause pitting.

Inspection Procedure

Accurate inspection is an important necessity for the life of any gear. The maximum life of any drive train can be obtained through proper inspection and repair procedures. Refer to "Tooling and Equipment" for a list of tooling for inspection. When you examine a gear, always use good lighting. If an unacceptable gear is reused, it is possible that the gear will fail. The gear that failed will destroy other components in the drive train. The technician that is performing the inspection should be familiar with all types of gear wear and damage. The most common reasons for gear failure are described in this Guideline. Decisions on reusing gears are helped by close inspections.

Illustration 28	g03880745
Use a clean, white piece of paper with a dull finish to reflect light onto the face of each gear tooth during the inspection process.

Use the following tools to identify damaged areas during the inspection process:

• Magnifying glass

• Strong light source

• White paper

Refer to Reuse And Salvage Guidelines, SEBF8148, "General Salvage and Reconditioning Techniques" for detailed information on inspection.

Process for Inspecting Gears

1. Clean all gears thoroughly before inspecting the gears. Refer to "Prepare the Area for Inspection"

2. Inspect the entire surface area of the gear for the following damage:

   • Pitting

   • Spalling

   • Cracking

   • Any other damage

   It is possible for only one tooth to be damaged.

3. Carefully inspect the bore of the gear with a bright light. Bearing bores for planetary gears can be sensitive to high loads and speeds. Careful inspection for damage is critical.

   1. Rim of gear

   2. Spline

   3. Bearing surface
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   Illustration 29	g03880746
   Notice the white plastic on top of the bench. It is easy to clean the surface. The surface reflects light. Also, the surface will not damage the gears on contact.

4. Bearing bores may have minimal wear or damage only.

5. Use Table 7 to ensure that the gear is inspected for all possible damage.

Table 7

Checklist for Inspecting Gears
Item	Yes	No
Normal wear
White layer flaking
Wear from high hour
Abnormal wear
Frosting
Pitting
Initial
Corrosive
Destructive
Spalling
Pitting or spalling
Scoring
Case crushing
Corrosion or corrosive pitting
Abrasive wear
Nicks
Cracks
Chipping
Uneven contact
Damage from foreign object
Rippling or Lipping
Bores in gears
Bores in planetary gears
Gears with replaceable bearing races

Scheduled Oil Sample Testing

An oil analysis that is certified by Caterpillar should be scheduled. The oil analysis should be based on the machine application and the schedule of hours. Change your oil regularly. Refer to the operating manual to acquire the recommended oil change intervals, oil capacity, and the type of oil. Regular oil changes and Scheduled Oil Samples are the best ways to discover oil contamination. Regular oil changes and Scheduled Oil Samples also prevent oil contamination. An SOS oil analysis may also help determine the cause of a failure.

Reconditioning

Gears with limited damage on the surface may be used again after the damaged area has been polished with 6V-2010 Polishing Stone and oil. Caterpillar recommends the use of a polishing stone and oil. Never use a die grinder to recondition a gear. A die grinder can remove the case hardened surface of a gear. Refer to Illustration 31.

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NOTICE
If the tooth has a raised metal area, remove only the raised portion on the tooth surface. Do not try to remove pitting or any other recessed surface damage. Do not use a grinder or power polisher, use only a hand-held stone. Using power tools to remove damage can also remove the case hardened surface of the gear, causing eventual failure.

Illustration 30	g03885189
6V-2010 Polishing Stone and oil should be used to polish a tooth. Be aware of the adjacent tooth. The corner of the stone can easily damage adjacent teeth.

Illustration 31	g03885193
A grinder had been used on this gear in an attempt to recondition the teeth. Use 6V-2010 Polishing Stone and oil for reconditioning the teeth on a gear. Do not use a grinder. The grinding process can remove the case hardened surface of a gear. DO NOT USE THIS PART AGAIN.

Machining

This section covers the basic stages that are required to machine a gear.

Illustration 32	g03885198
The horizontal marks were created during the manufacturing process. These marks are rough machining marks. The marks are not really cracks. Use one of the inspection methods to make sure that the marks are not cracks. USE THIS PART AGAIN.

Illustration 33	g03885204
The burrs that are on the gear are not lipping. The machining process can leave burrs on the edges of gear teeth. Dull cutting tools can cause burrs. USE THIS PART AGAIN.

Rough Machining

The gear teeth are often machined by using a hob process. If a gear has been through a hob process, it is easy to notice the rough machining marks on the surfaces of the teeth and the burrs on the edges of the teeth .

Illustration 34	g03885207
This gear has been through the rough machining process. A hob tool was used in this process.

Illustration 35	g03885209
The marks from the hob (1) are visible on the face of the tooth on the gear in the image. The rough machining marks and burrs that are left from the hob process will be removed during the final machining process.

Finish Machining

A machining process is used after the gear teeth have been cut with the hob process. This process is called shaving. Illustration 36 shows the appearance of a new gear that has passed through the process of shaving. This gear is ready for heat treatment.

Illustration 36	g03885212
The image shows a new gear that has not been through the heat treat process. The marks from shaving (2) that are shown in Illustration 36 will be visible after many of hours of use. These marks are positioned on the face of the tooth at a slight angle. The area of the root fillet is not a contact surface so the area of the root fillet does not need the final machining process. The marks from the hob (1) will be left in the root fillet. This gear is ready for heat treatment.

Illustration 37	g03885213
The marks from shaving (2) and the marks from the hob (1) are more visible in the magnification of Illustration 36.

Illustration 38	g03885215
The wear pattern of the gear that is shown in the illustration is an ideal wear pattern. The pattern of wear is centered and even on the tooth. During operation of the gear train, the marks from shaving will slowly wear away. Notice that the contact ends before reaching the tip of the gear tooth. The gear teeth are designed to reduce the occurrence of chipping at the edges and scoring at the tips. USE THIS PART AGAIN.

Illustration 39	g03885217
The image shows marks from the hob (1). Inspect the gear for cracks with any of the methods for inspecting cracks. USE THIS PART AGAIN.

Illustration 40	g03885218
A machining mark may look like a crack. Inspect the gear with any of the methods for inspecting cracks if the gear appears to have a crack. Machining marks should not appear while detecting cracks. The machining marks are not commonly deep. Normal wear will smooth the surfaces and normal wear should be evenly distributed across the teeth. USE THIS PART AGAIN.

Normal Wear

This section will describe the types of normal wear patterns that can develop by a gear. Normal gears consist of white layer flaking, and wear from high hours. Usually, gears that only have normal wear can be used again.

Illustration 41	g03885223
Normal wear is shown in this illustration. The machining marks are shown by the arrows. The machining marks are still visible on this gear. USE THIS PART AGAIN.

Illustration 42	g03886510
Tooth wear is shown in this illustration. Wear pattern is reasonably centered. Wear is through all machining marks, but does not appear excessive. USE THIS PART AGAIN.

Illustration 43	g03886515
Tooth wear pattern is shown in this illustration. Well-defined contact edge. USE THIS PART AGAIN.

Illustration 44	g03886717
Tooth wear pattern is shown in this illustration. Pattern appears normal. USE THIS PART AGAIN.

Illustration 45	g03886721
High tooth wear pattern is shown in this illustration. Pattern appears normal. USE THIS PART AGAIN.

Illustration 46	g03886939
Tooth wear pattern is shown in this illustration. Wear pattern appears normal. USE THIS PART AGAIN.

Illustration 47	g03886948
The illustration shows tooth wear pattern. Wear pattern appears normal. USE THIS PART AGAIN.

White Layer Flaking

Gears that are hardened by nitride develop a thin brittle skin (2) that may flake off during normal operation. White layer flaking is a normal type of gear wear. Most gears that show signs of white layer flaking can be used again.

Illustration 48	g03885226
White layer flaking (1) is shown. The flaking of the skin appears to be destructive, but the flaking is not destructive. The gear may be reused. USE THIS PART AGAIN.

Illustration 49	g03885230
The image is a magnified view of the thin brittle skin (2) that can develop on gears that are hardened by nitride. USE THIS PART AGAIN.

Illustration 50	g03885233
The rough machining marks have caused the load to become concentrated in certain areas. The pattern of the white layer flaking follows the machining marks. USE THIS PART AGAIN.

Illustration 51	g03886823
The seal pick points to white layer flaking. This is a normal result of heat treat operations. The gear may be reused. USE THIS PART AGAIN.

Wear from High Hours

The surfaces of gears begin to wear and the surfaces become smooth when loads are applied to gears. This smooth surface should occur over approximately two-thirds or more of the length of the gear tooth. Refer to Illustration 52 and Illustration 53.

Illustration 52	g03885234
The gear illustrates normal wear from high hours. This gear may be reused after checking for other types of abnormal wear. The alignment should be adjusted so that the wear will be centered on the teeth of this gear. USE THIS PART AGAIN.

Illustration 53	g03885236
Normal wear is shown in this illustration. The machining marks are shown by the arrows. The machining marks are still visible on this gear. USE THIS PART AGAIN.

Abnormal Wear

This section describes the different types of abnormal wear.

Frosting

Frosting occurs when gear teeth that are mating undergo metal-to-metal contact. The metal contact usually results from an inadequate film of oil between the surfaces of mating gear teeth. Frosting is not harmful to a gear if pitting has not started. Frosting is not harmful to a gear if the profile has not changed. Frosting appears as a cloudy gray area on the surface of gear contact. Gears that appear to have signs of frosting can be used again if the gear is free from other types of damage. Frosting may be a result of the following problems:

• High operating temperatures that cause the viscosity of lubrication to become thin

• High loads

• Incorrect lubrication

• Incorrect part

Other similar problems may result in frosting. Frosting is not harmful to the gear. If the conditions that cause the frosting are not corrected, pitting could result. Pitting can lead to destructive pitting and spalling.

Illustration 54	g03885406
Frosting appears on the surface of gear contact and frosting usually occurs in an even wear pattern. Frosting is displayed in the illustration as small pits on the surface that are along the pitch line. Always check for pitting damage and damage to the profile of the gear before reusing a gear that has frosting.

Illustration 55	g03885423
Correct the cause of frosting to avoid pitting. An example of frosting appears as a cloudy gray area on the surface of gear contact. The condition is caused by an inadequate film of oil between two surfaces of gear teeth that are mating. There is no pitting in this example. USE THIS PART AGAIN.

Illustration 56	g03887754
Correct the cause of frosting to avoid pitting. The seal pick points to frosting which appears as a cloudy gray area on the surface of gear contact. The condition is caused by an inadequate film of oil between two surfaces of gear teeth that are mating. There is no pitting in this example. USE THIS PART AGAIN.

Illustration 57	g03885426
This is an example of frosting. This gear may be reused because there is no pitting. Correct the alignment of the load during the installation process. USE THIS PART AGAIN.

Illustration 58	g03885431
Pitting (1) is shown on the gear. Frosting (2) is also shown. Frosting (2) is acceptable. Destructive pitting will usually occur with frosting (2). Refer to"Pitting" to determine that pitting (1) is not destructive. The gear may be reused after determining that pitting (1) is not destructive. USE THIS PART AGAIN.

Illustration 59	g03886520
Area below frosting appears to be a non-micropitting zone. USE THIS PART AGAIN.

Illustration 60	g03885437
Reusing the gear depends on the application, operation, and maintenance. BORDERLINE

Pitting

Pitting is the development of small holes in the surface of a tooth. Pitting is caused by stress that is caused by fatigue from contact on the surface of a gear tooth. The holes mainly develop on the lower part of a gear tooth near the LPSTC of the drive gear. There are two types of pitting.

Initial Pitting - Initial pitting will usually occur during the period of break-in that is up to 500 hours. Instances of initial pitting will seldom progress into destructive pitting if the application, operation, and maintenance are correct. Initial pitting will usually stop once the period of break-in is complete.

Destructive Pitting - Destructive pitting will usually occur after the period of break-in up to 500 hours. Destructive pitting will usually be found on most of the gear teeth. The deep pits will progress into spalling and a fracture if the causes of destructive pitting are not corrected.

Illustration 61	g03885441
Notice the small pits that are located near the lowest point of single tooth contact on this gear tooth.

Illustration 62	g03885446
Initial pitting (3) should not progress into destructive pitting. Check for other types of abnormal wear before reusing this gear. USE THIS PART AGAIN.

Illustration 63	g06092920
This Illustration is a magnification of Illustration 62. USE THIS PART AGAIN.

Illustration 64	g03885447
The arrows show an instance of initial pitting. Lightly polish the area with a 8T-7765 Surface Reconditioning Pad and oil. USE THIS PART AGAIN.

Illustration 65	g06092928
This arrow points to initial pitting just at the start of active profile on the gear. Check for other types of abnormal wear before you reuse this gear. USE THIS PART AGAIN.

Illustration 66	g03886492
The seal pick points to a very small pit. Reuse if similar pitting is not found on most of the gear teeth or consecutive gear teeth. USE THIS PART AGAIN.

Illustration 67	g03886748
The illustration shows a small pit. USE THIS PART AGAIN.

Illustration 68	g03886986
The seal pick points to very small pits. USE THIS PART AGAIN.

Illustration 69	g03886991
The seal pick points to small pits at high pitch line in a highly loaded portion of the tooth. The pitting appears to elongate which indicates it is becoming destructive. DO NOT USE THIS PART AGAIN.

Illustration 70	g03886993
The illustration shows tooth tip pitting. Do not reuse when pitting is found near the tip on multiple teeth. The tooth tip should be an area of no contact. DO NOT USE THIS PART AGAIN.

Illustration 71	g03887002
This illustration shows multiple pits in the middle of the tooth. Do not reuse as the pitting occurs at the pitch line. DO NOT USE THIS PART AGAIN.

Illustration 72	g03887015
This illustration shows small tooth pitting that has developed from micro pitting. DO NOT USE THIS PART AGAIN.

Illustration 73	g03887023
This illustration shows small tooth pitting that has developed from micro pitting. DO NOT USE THIS PART AGAIN.

Illustration 74	g03887025
This illustration shows small tooth pitting that has developed from micro pitting. DO NOT USE THIS PART AGAIN.

Illustration 75	g03887030
This illustration shows small tooth pitting that has developed from micro pitting. The pitting has also occurred at the high loaded region of the tooth. DO NOT USE THIS PART AGAIN.

Illustration 76	g03887009
The illustration shows a large deep pit. Do not reuse as large pit will progress into spalling. DO NOT USE THIS PART AGAIN.

Destructive Pitting

Destructive pitting usually occurs after 500 hours of operation. Destructive pitting can be found on most of the gear teeth. The micro-pitting can lead to destructive pitting and progress into spalling. The tooth with spalling will eventually fracture.

Illustration 77	g03885496
Destructive pitting is shown in this illustration. The large pits across the Lowest Point of Single Tooth Contact are destructive pits. Destructive pitting can penetrate the case hardened surface of a gear.

Illustration 78	g06092935
Micro-pitting (4) may occur if the film of lubrication is inadequate. The micro-pitting is a type of destructive pitting that can be caused by metal contact. The micro-pitting is at an early stage. This gear can be used again. Determine the cause of insufficient lubrication. Correct the cause of insufficient lubrication before reinstalling the gear. USE THIS PART AGAIN.

Illustration 79	g06092943
The seal pick is showing early hour micro pitting at the root of the tooth. This is early stage wear and the part can be reused. USE THIS PART AGAIN.

Illustration 80	g03885502
Notice that destructive pitting (6) is much deeper than initial pitting (5). Destructive pitting is near the LPSTC. The destructive pitting has penetrated the case hardened surface. DO NOT USE THIS PART AGAIN.

Illustration 81	g03885507
Magnified view of micro pitting. USE THIS PART AGAIN.

Illustration 82	g03887028
Destructive pitting is shown in this illustration. The pit is large and deeper than initial pitting. DO NOT USE THIS PART AGAIN.

Illustration 83	g03885511
The pitting is extensive with many deep pits on multiple teeth. The pitting has penetrated the case hardened surface. DO NOT USE THIS PART AGAIN.

Illustration 84	g03885517
Micro pitting is seen on a high load region of the tooth. Reusing the gear depends on application, operation, and maintenance. BORDERLINE

Illustration 85	g03885520
The pitting on this gear is at the threshold. Check for other types of abnormal wear. Base the decision on the application, operation, and maintenance of the machine. Inspect the dent to determine there are no sharp edges present. BORDERLINE

Illustration 86	g03885522
Micro-pitting (7) and Macro-pitting (8) are shown in the illustration. This gear cannot be reused because the macro pitting is developing into spalling. DO NOT USE THIS PART AGAIN.

Illustration 87	g03886529
The seal pick points to micropitting. Micropitting at start of active profile. Wear appears normal. USE THIS PART AGAIN.

Illustration 88	g03886690
The seal pick points to micropitting. USE THIS PART AGAIN.

Illustration 89	g03886699
The illustration shows micropitting. USE THIS PART AGAIN.

Illustration 90	g03886963
The illustration shows micropitting. USE THIS PART AGAIN.

Illustration 91	g03886979
The illustration shows micropitting. USE THIS PART AGAIN.

Illustration 92	g03886982
The seal pick points to micropitting. USE THIS PART AGAIN.

Illustration 93	g06092951
The seal pick points to micropitting at the root of the tooth. USE THIS PART AGAIN.

Illustration 94	g06092959
Micropitting seen at tip of tooth. Part may be reused. USE THIS PART AGAIN.

Illustration 95	g06092966
Micropitting is seen at tip of tooth. No additional wear is seen. USE THIS PART AGAIN.

Spalling

Spalling is a type of failure from fatigue that occurs under the surface. Spalling is a result of a small crack that has passed through the face of the gear tooth and under the case hardened surface. Either destructive pitting or case crushing can cause spalling. Destructive pitting is usually the starting point for spalling. Spalling travels from the destructive pit up the face of the tooth. Throughout this process, the crack will remain beneath the case hardened surface. When a crack travels beneath the case hardened surface of a gear tooth, the crack travels along the path of least resistance. As the crack under the surface progresses toward the tip of the tooth, the case hardened surface will break into small pieces. These pieces will continue to break until the spalling has reached the tip of the tooth. Spalling will form in the shape of a V. This process happens over a length of time. Once the protective case hardened surface has deteriorated, the weak inner core will be left unprotected. A tooth that has spalling damage will eventually fracture. Schedule an SOS to detect spalling damage in the drive train. If necessary repairs are not made, teeth with spalling can fracture. Teeth that fracture can cause significant damage to the drive train. Do not reuse any gear that has spalling damage.

Note: Spalling is often confused with the case crushing. It is important to know the differences.

1. Destructive pitting is the main cause of spalling. Look for instances of destructive pitting. The damage may be due to the case crushing if destructive pitting is not present.

2. Examine the damaged area. Spalling will not leave pieces of crushed metal. Case crushing will leave pieces of the case.

3. When a gear tooth has spalling damage, the shape of the damage will be in a triangular shape. Damage from a crushed case is usually in a rectangular shape.

4. Refer to "Case Crushing" in this guideline for more information.

Before spalling occurs, the outline in the face of the tooth will be visible. The outline of spalling damage will be a triangular shape and the tip of the triangle will point downward. Do not reuse any gear with an outline on the face of the tooth in the shape of a triangle.

Once the spalling progresses, the case hardened surface will slowly break. Examples of spalling damage are shown in the next photos. Do not reuse any gear with spalling damage.

Illustration 96	g03885587
Notice that the spalling starts at the destructive pitting. The spalling climbs toward the tooth. The spalling is in a triangular shape. Illustrations 97 through 101 show the growth of spalling. The tip of the tooth (9) and fillet of the tooth (10) will be called out in the following illustrations.

Illustration 97	g03885591
Stage 1 The starting point of spalling is visible. The starting point is shown below the pitch line. DO NOT USE THIS PART AGAIN.

Illustration 98	g03885598
Stage 2 Stage 2 shows a small crack from fatigue at the surface of the gear. Metal starts to flake off the face of the tooth. DO NOT USE THIS PART AGAIN.

Illustration 99	g03885644
Stage 3 The small cracks under the surface will join and the face of the tooth will flake. DO NOT USE THIS PART AGAIN.

Illustration 100	g03885647
Stage 4 The small cracks under the surface are shown. The cracks join as the area of spalling becomes larger. DO NOT USE THIS PART AGAIN.

Illustration 101	g03885649
Stage 5 The spalling has progressed across the face of the tooth. Stage 6 will be a fracture. DO NOT USE THIS PART AGAIN.

Illustration 102	g03885653
The arrow shows an area on the gear tooth that contains spalling in an early stage. Pits are becoming connected by small cracks that are under the surface. DO NOT USE THIS PART AGAIN.

Illustration 103	g03885655
Pieces of the face of the tooth will flake off as the cracks that are under the surface grow. DO NOT USE THIS PART AGAIN.

Illustration 104	g03885744
Most spalling develops in a triangular shape. The triangular shape is not always characteristic. Even if the shape is not triangular, spalling will grow as the spalling progresses up the face of the tooth. DO NOT USE THIS PART AGAIN.

Illustration 105	g03885748
The spalling has originated from pitting damage. DO NOT USE THIS PART AGAIN.

Pitting and Spalling

A combination of pitting and spalling occurs during the process of transition between pitting and spalling. The wear is due to the sliding and rolling action between the teeth. A gear with evidence of pitting and spalling should not be used again. Spalling can progress rapidly into a fracture. Illustration 106 is a cross section of the spalling prior to a fracture.

Illustration 106	g03885763
This is a cross section of the succession from pitting to spalling. Notice that the destructive pitting has caused cracks that are under the surface in the hardened tooth surface.

Illustration 107	g03885781
The image shows a cross section of a tooth with spalling. Notice that the destructive pitting can cause cracks under the surface in the case hardened surface of the tooth. DO NOT USE THIS PART AGAIN.

Illustration 108	g03885785
Spalling is a type of fracture under the surface from fatigue. Spalling causes metal to flake. Spalling can progress rapidly into a fracture. Notice that the cracking under the surface can cause a triangular shaped outline on the face of the tooth. The area will fracture and the area will appear similar to the damage that is shown in Illustration 108. DO NOT USE THIS PART AGAIN.

Illustration 109	g03885788
Notice that the spalling progresses up the face of the tooth from the destructive pitting at the bottom of the tooth. The spalling is in a triangular shape. DO NOT USE THIS PART AGAIN.

Illustration 110	g03885793
Destructive pitting (11) is shown along the lowest point of single tooth contact and destructive pitting (12) is shown near the pitch line. Cracking under the surface exists just beneath the destructive pitting. The destructive pitting is in the process of progressing into spalling. The spalling on the front of the tooth will appear similar to the spalling on the back of the tooth. Spalling (13) is shown progressing from the destructive pitting to the highest point of single tooth contact. The spalling is triangular in shape.

Illustration 111	g03885796
The Illustration shows a cross section of fatigue from spalling that is early stage. Detecting fatigue from spalling in an early stage is difficult. The spalling starts in the core of the gear. Fatigue from spalling can rapidly progress into a fracture once the cracks reach the case hardened surface.

Corrosion and Corrosive Pitting

Corrosion may be caused by an electrolyte that has entered the lubrication system. The most common electrolyte is water. Corrosion can lead to corrosive pitting. Correct the cause of corrosion before corrosive pitting occurs. If an electrolyte enters the drive train, the electrolyte can neutralize the additive package in the oil.

Early stages of corrosion are not harmful. Most corroded gears can be used again if pitting has not occurred. During the rebuild, repair the point of entry for the electrolyte.

Rust is a common type of corrosion. Check for corrosive pitting after you remove the corrosion.

Illustration 112	g03885822
Corrosion has caused corrosive pitting. The pitting covers a good percentage of this gear tooth. DO NOT USE THIS PART AGAIN.

Illustration 113	g03885824
Corrosive pitting will take over the entire face of a gear tooth in an advanced stage. This stage of corrosive pitting is followed by spalling. DO NOT USE THIS PART AGAIN.

Illustration 114	g03885828
The corrosive pitting has developed into spalling. DO NOT USE THIS PART AGAIN.

Illustration 115	g03885831
The gear may be used again because the corrosive pitting is only on the ends of the gear teeth. USE THIS PART AGAIN.

Illustration 116	g03885833
This image shows a gear that has undergone corrosion. Corrosion may create shallow surface deposits. Shallow surface deposits visually appear as discoloration. Use a microscope to examine the deposits. Do not reuse the gear if the gear shows signs of pitting. The gear has been examined. The gear does not show any signs of pitting. USE THIS PART AGAIN.

Illustration 117	g03885837
Remove the rust that is on this gear. Corrosion will cause corrosive pitting if the source of the problem is not corrected immediately. The source of corrosion is usually water. DO NOT USE THIS PART AGAIN.

Illustration 118	g03885840
Pits from rust (14) are visible in the illustration. The gear should not be used again because rust has caused pitting on the teeth of this gear. DO NOT USE THIS PART AGAIN.

Illustration 119	g03885845
Corrosion only affects the appearance of the gear tooth. The texture remains smooth. There are no signs of pitting. Corrosive pitting has not yet occurred. Correct the cause of the corrosion before reusing this gear. USE THIS PART AGAIN.

Illustration 120	g03885855
This gear may not be used again because the gear is heavily rusted. The cause of the rust is usually water that mixes with the oil. Check the gears for rust and replace the gears if replacement is necessary. Make sure that the source of moisture has been eliminated before rebuilding the drive train. DO NOT USE THIS PART AGAIN.

Illustration 121	g03885858
The corrosion in this illustration has not caused pitting. USE THIS PART AGAIN.

Illustration 122	g03885863
The corrosion that is shown in the illustration has progressed past the first stage of corrosion. The gear may appear to be reusable, but this gear should not be reused. Good lighting and magnification will reveal that the gear tooth is discolored and rough. DO NOT USE THIS PART AGAIN.

Adhesive Wear (Scoring)

Scoring can result from metal to metal tooth contact. Scoring can cause vertical scratches that are perpendicular to the pitch line. Scoring begins above the pitch line and below the pitch line. Scoring develops when sliding action occurs between two mating teeth. Scoring damage should not occur at pitch line because only rolling action is present at this location. Scoring can occur with inadequate oil, periods of excessive load, speed, and misalignment. Severe scoring will produce an irregular surface with wrinkles and depressions on the tooth face. Reuse a gear with scoring damage only if the face of the tooth is relatively smooth and only if the scoring has not altered the shape of the tooth profile. Inspect the gear for cracks with any of the methods for inspecting cracks.

Illustration 123	g03885867
Scoring usually occurs above the pitch line or below the pitch line. Scoring is the result of metal to metal tooth contact.

Illustration 124	g03885871
Scoring (15) is shown at an early stage in this illustration. The gear may be used again because the scoring is in an early stage. USE THIS PART AGAIN.

Illustration 125	g03885876
This is a magnification of Illustration 124. The scoring has not penetrated the case hardened surface. USE THIS PART AGAIN.

Illustration 126	g03885879
The scoring is located above pitch line (16) and the scoring is located below pitch line (16). There is only rolling action at the pitch line. Scoring will not occur at the pitch line because of rolling action. DO NOT USE THIS PART AGAIN.

Illustration 127	g03885882
The marks from shaving in the illustration were made during the final operation of machining. The marks from shaving are shown by the arrows. Marks from shaving can be confused with scoring marks. Marks from scoring are vertical. Shaving marks will be positioned at a slight angle. Shaving marks will cover the entire width of the face of the tooth. The marks from shaving that are shown in the illustration are not harmful. Refer to "Machining" for additional information. USE THIS PART AGAIN.

Illustration 128	g03885884
The arrows in this illustration show scoring marks that are excessive enough to make this gear unusable. Notice that damage is below the pitch line. DO NOT USE THIS PART AGAIN.

Illustration 129	g03885889
Check the profile of each gear tooth. Do not use this gear again if the profile has changed. BORDERLINE

Illustration 130	g03885890
This gear may be reused if scoring damage above the pitch line is smooth and the profile has not changed. USE THIS PART AGAIN.

Illustration 131	g03885891
This illustration is a magnified view of Illustration 130.

Illustration 132	g03885892
The scoring is above the pitch line. The scoring appears to be vertical scratches. The gear may be used again because the face of the tooth is smooth. USE THIS PART AGAIN.

Illustration 133	g03887789
This bevel gear maybe reused if the profile is smooth and not damaged. USE THIS PART AGAIN.

Illustration 134	g03887821
The scoring is above the pitch line. The scoring appears to be vertical scratches. This bevel gear may be reused if scoring damage is smooth and the profile has not changed. USE THIS PART AGAIN.

Illustration 135	g03887834
This bevel gear may be reused if scoring is smooth and the profile has not been damaged. USE THIS PART AGAIN.

Illustration 136	g03887876
This bevel gear may be reused if scoring damage is smooth and the profile has not changed. USE THIS PART AGAIN.

Illustration 137	g03889736
This bevel gear may be reused if scoring damage is smooth and the profile has not changed. USE THIS PART AGAIN.

Illustration 138	g03889743
This bevel gear may be reused if scoring damage is smooth and the profile has not changed. USE THIS PART AGAIN.

Illustration 139	g03887885
The arrows in this illustration show scoring marks that are excessive enough to make this gear unusable. The profile appears to be damaged from scoring. DO NOT USE THIS PART AGAIN.

Illustration 140	g03889715
The profile of this bevel gear appears to be damaged from scoring DO NOT USE THIS PART AGAIN.

Illustration 141	g03889727
This bevel gear may be reused if scoring damage is smooth and the profile has not changed. USE THIS PART AGAIN.

Illustration 142	g03885893
Lipping damage (17) has changed the profile of the tooth. A gear with lipping damage should not be used again. DO NOT USE THIS PART AGAIN.

Illustration 143	g03885894
Severe scoring has damaged the profile of the teeth on this gear. DO NOT USE THIS PART AGAIN.

Illustration 144	g03885896
Tooth profile (18) is damaged and irregular. Notice that the scoring has changed the profile of the tooth. DO NOT USE THIS PART AGAIN.

Illustration 145	g03885897
Scoring has damaged the tooth profile. A corrected alignment of the load will help to prevent the same type of damage to the replacement gear. Locate the cause of the misalignment of the load and correct the cause of the misalignment of the load. DO NOT USE THIS PART AGAIN.

Illustration 146	g03885899
This gear has medium-sized abrasive wear. Use a 6V-2010 Polishing Stone to polish lightly the rough edges before reusing the gear. The gear may be reused because the abrasive wear is toward the tip of the teeth. Always check the profile to ensure that the profile is free from damage. USE THIS PART AGAIN.

Case Crushing

Case crushing is a failure of the case hardened surface of a gear. The case is the surface and the core is the center. The case of a tooth is much harder than the core of a tooth. Case crushing appears similar to an object that has been pulverized. When case crushing occurs, the softer core may become exposed. The core of a gear is unable to withstand the normal loads. Gear teeth with crushed cases will quickly fracture. Gears with evidence of case crushing cannot be used again.

Illustration 147	g03886061
The case hardened wear surface has failed and the core is exposed. Gears with a crushed case should not be reused because the soft core is unable to withstand the normal loads.

The following problems can cause case crushing:

• Misalignment

• Overload

• Shock load

• Excessively thin case

• Excessively soft core

Gears with evidence of case crushing should not be reused. Gears should be checked for cracks if shock loading is suspected, or a failure has occurred. Inspect gears for cracks with any of the methods for inspecting cracks.

Illustration 148	g03886074
This illustration shows a cross section of a gear. The components consist of hardened case (19) and softer inner core (20).

Illustration 149	g03886077
The gear has been cut by a saw. The gear has been polished. The gear has been etched with acid. In this cross section, the case hardened surface is visible. Every Caterpillar gear goes through a proprietary heat treat process.

Illustration 150	g03886079
Evidence of case crushing is shown. DO NOT USE THIS PART AGAIN.

Illustration 151	g03886082
Case crushing is shown in the illustration above. The cracks in the face of the tooth are in an early stage, and the cracks are barely visible. Inspect the gear for cracks with any of the methods for inspecting cracks. DO NOT USE THIS PART AGAIN.

Illustration 152	g03886085
Horizontal cracks across the face of the tooth will become visible as a gear progresses through the stages of case crushing. The pulverized appearance is unique to case crushing. DO NOT USE THIS PART AGAIN.

Illustration 153	g03886088
In the final stage of case crushing, material from the face of the tooth will flake off. The edges to the cavity are sharp and perpendicular to each other. Distinguishing the difference between damage from case crushing and spalling damage can be difficult. The cavity that results from a crushed case is larger than the cavity that results from spalling. Experience is the best guide when you need to distinguish the difference between the two types of damage. DO NOT USE THIS PART AGAIN.

Abrasive Wear

Abrasive wear is caused by small contaminants in the lubrication system such as the following:

• Soil

• Sand

• Metal

The small particles will eventually wear down the surface of the teeth. The small particles can even alter the profile of a gear. Abrasive material can travel throughout the gears in the drive train and abrasive material can damage other gears as well. Check all the gears in the drive train if one of the gears has abrasive wear. Light abrasive material will cause the gear to appear dull in color. The smallest contaminants will lightly polish the teeth of a gear. If light abrasive wear is not corrected, the teeth will become shiny enough to resemble a mirror. Larger sized contaminants will usually produce scratches, cuts, and bruises on the gear teeth. Large particles can create deep grooves on the face of the tooth. If evidence of abrasive wear is found, correct the source of the contamination immediately. Gears with limited abrasive wear may be reused if the profile has not changed and the gear does not have any other types of damage.

Illustration 154	g03886093
This illustration shows a diagram of advanced abrasive wear (22) around the area of the pitch line (21). Advanced abrasive wear will alter the tooth profile.

Illustration 155	g03886098
The gear that is shown in this illustration is in an early stage of the process of abrasive wear. The teeth on this gear have a shiny appearance with no flat spots on the profile. The gear can be used again after you correct the source of the contamination. USE THIS PART AGAIN.

Illustration 156	g03886101
The teeth on this gear appear to have a shiny finish. The abrasive wear has advanced from the early stages of abrasive wear. The early stage of abrasive wear was displayed in the previous illustration. Notice the machining marks and polishing marks on the right side of the teeth. The machining marks are still visible toward the tips of the gear teeth. USE THIS PART AGAIN.

Illustration 157	g03886105
This is the next stage in the process of abrasive wear. When abrasive wear is allowed to continue, the gear teeth will develop a finish that resembles a mirror. Each tooth will reflect an image of the adjacent tooth. DO NOT USE THIS PART AGAIN.

Illustration 158	g03886107
Notice the areas above the pitch line and below the pitch line. The scratching on the surface of these teeth show that large foreign particles were present in the lubrication system. The normal sliding action is responsible for this large amount of wear above the pitch line. Bruising has also occurred on the teeth of the gear. DO NOT USE THIS PART AGAIN.

Illustration 159	g03886108
This gear has been exposed to a significant amount of abrasive wear. The arrow in this illustration indicates a heavy wear groove. A significant amount of abrasive wear is capable of causing a depression. DO NOT USE THIS PART AGAIN.

Illustration 160	g03886111
The case hardened surface has been worn away and the surface has exposed the softer core. This damage will quickly progress into a fracture. DO NOT USE THIS PART AGAIN.

Nicks

Nicks usually occur when a gear is not handled properly before heat treatment. Because most nicks will occur before heat treatment, a gear with a nick can be reused.

Illustration 161	g03886118
This gear has a nick on the tip of the tooth.

USE THIS PART AGAIN.

Illustration 162	g03886121
Nick (23) occurred before heat treatment. Before reusing this gear, verify that the damage is not a crack. USE THIS PART AGAIN.

Illustration 163	g03886124
This tooth has been nicked on the face and in the fillet. Before reusing this gear, verify that the damage is not a crack. USE THIS PART AGAIN.

Illustration 164	g03886130
The nick that is shown on this gear is on the tip. Nicks on a tip or nicks on an edge are acceptable if the nicks do not extend onto the surface of tooth contact. Use a 6V-2010 Polishing Stone and oil to polish the rough edges around the nick. USE THIS PART AGAIN.

Illustration 165	g03886545
The nick that is shown on this gear is impact damage. Appears to have been caused by handling, possible in green state. If there are any doubt, check for cracks. USE THIS PART AGAIN.

Illustration 166	g03886676
The seal pick points to impact damage. Appears to have been cause by something going through the mesh. Recommendation is to check for cracks, and use a 6V-2010 Polishing Stone stone to remove high spots & reuse. USE THIS PART AGAIN.

Illustration 167	g03886683
Damage at end of tooth. Possible that this type of damage was caused during sun gear manufacture. USE THIS PART AGAIN.

Illustration 168	g03886952
Tooth surface gouges. Machining marks are still visible at the bottom of the gouges, and damage/distress has been done & not advancing. If gouges were horizontal, recommendation would be to replace the gear. USE THIS PART AGAIN.

Cracks

It is difficult to distinguish visually a difference between a scratch and a crack. Inspect the gear for cracks with any of the methods for inspecting cracks. Refer to "Metallurgy" for more information about the necessary equipment and procedures that are needed to determine if cracks are present.

Illustration 169	g03886137
The cracks are located in the fillet of the tooth. 4C-4804 Penetrant has been used to detect the cracks that are shown in the illustration. DO NOT USE THIS PART AGAIN.

Illustration 170	g03886141
This gear has a crack toward the end of the tooth. The liquid fluorescent method has been used to find the crack that is shown in this illustration. DO NOT USE THIS PART AGAIN.

Illustration 171	g03886150
Cracks have developed in the roots of this gear. It was necessary to use the method for the dry magnetic particle to locate these cracks. DO NOT USE THIS PART AGAIN.

Illustration 172	g03886155
The crack in the root of the tooth has progressed toward the bore of the gear. Finding a crack can be difficult and one of the methods for detecting cracks must be used. DO NOT USE THIS PART AGAIN.

Illustration 173	g03886159
The crack has developed in the root between two teeth. The crack has progressed all the way through the gear. DO NOT USE THIS PART AGAIN.

Chipping

The wear pattern should be checked on gears with chipping. Misalignment will cause loading off the end of the tooth. The misalignment can cause chipping. Multiple teeth typically become chipped under a misaligned load.

Illustration 174	g03886164
The chip on this gear is from not handling the gear properly. Unlike a nick, a chip will occur after heat treatment. USE THIS PART AGAIN.

Illustration 175	g03886172
The image is a magnified view of Illustration 175. USE THIS PART AGAIN.

Illustration 176	g03886176
The ends of the teeth are chipped because foreign objects have damaged the teeth. Polish the sharp edges with a 6V-2010 Polishing Stone and oil. Inspect the gear for cracks by using any of the methods for inspecting cracks. USE THIS PART AGAIN.

Illustration 177	g03886180
The end of the tooth has been chipped because the gear has not been handled properly. Since this chip extends into fillet (24), the gear should not be reused. The tooth may break during operation and the broken tooth may cause significant damage to other components in the drive train. DO NOT USE THIS PART AGAIN.

Illustration 178	g03886186
The damage from shipping extends onto the contact surface of the gear tooth. DO NOT USE THIS PART AGAIN.

Illustration 179	g03886189
Chip (25) does not extend onto the contact surface. Polish the rough edges that are around chip (25) with a stone and oil. USE THIS PART AGAIN.

Uneven Contact

Illustration 180	g03886202
The five most common types of uneven wear patterns are shown in this illustration. Normal contact pattern (30) will lead to a maximum life if the application, the operation, and the maintenance procedures are adequate. Contact on the end of the tooth (31) can lead to breakage. Contact at the tip of the tooth (32) can lead to scoring, pitting, and breakage. The contact that is concentrated at the root (33) can lead to scoring and pitting. The contact that is concentrated at the tip (34) can lead to scoring, pitting, and breakage. (30) Normal contact pattern (31) Contact on the end of the tooth (32) Contact at the tip of the tooth (33) Contact that is concentrated at the root (34) Contact that is concentrated at the tip

Illustration 181	g03886208
Contact on the end of the tooth is shown. Contact pattern (31) is shown in the illustration. The contact is highly concentrated toward the end of the tooth. Because the contact pattern is not centered on the tooth, this gear should not be used again. DO NOT USE THIS PART AGAIN.

Illustration 182	g03886218
Contact on the end of the tooth is shown. This is a typical example of a severe wear step. The contact pattern is not centered on the tooth. DO NOT USE THIS PART AGAIN.

Illustration 183	g03886220
Contact on the end of the tooth is shown. The arrows in this illustration point out severe wear steps. This type of wear is also caused by an uneven contact pattern. DO NOT USE THIS PART AGAIN.

Damage from Foreign Objects

Foreign objects are objects that are not permitted in the drive train. A foreign object will commonly come from the drive train. Under harsh conditions, gear teeth and roller bearings can break. The foreign objects can damage other components in the drive train. Broken teeth from other gears and pieces of failed bearings are the two most common types of foreign objects.

Damage from foreign objects must not penetrate the case hardened surface of a gear. The contact surface of a gear may have only a small amount of damage from foreign objects. Damage from foreign objects must not exist in the fillets on the gear.

Damage from foreign objects should not exist on the face of the teeth on a gear.

Do not reuse a gear if more than one of the following are true:

• Significant amounts of damage from foreign objects on a gear

• Damage from foreign objects will affect the distribution of the load.

• Damage from foreign objects affects the film of lubrication.

• Damage from foreign objects exists in the fillet.

• Damage from foreign objects has penetrated the case hardened surface.

• Damage from foreign objects is on the threshold of reusing.

Refer to the "Reconditioning" section to recondition the damage from foreign objects. If the contact surface near the damage will not become stressed under a normal load, the gear may be reused.

Illustration 184	g03886225
The illustration shows the typical example of a planetary gear set. Sun gears and planet gears are external gears. Ring gears are internal gears. (35) Ring gears (36) Sun gears (37) Planet gears

Illustration 185	g03886229
Damage from foreign objects (38) is large and deep. The damage is also near the fillet. DO NOT USE THIS PART AGAIN.

Illustration 186	g03886231
The damage from foreign objects on this gear is just above the pitch line. USE THIS PART AGAIN.

Illustration 187	g03886234
The damage from foreign objects is at the pitch line. Use inspection methods to determine if damage has smooth or sharp edges. USE THIS PART AGAIN.

Illustration 188	g03886236
The damage is at the pitch line and the damage is below the pitch line. The damage that is below the pitch line does not extend into the fillet. Damage does not show any sharp edges. USE THIS PART AGAIN.

Illustration 189	g03886238
Damage from foreign objects (39) that is next to the pitch line is acceptable. However, because damage (40) extends into the fillet of the tooth, this gear cannot be reused. DO NOT USE THIS PART AGAIN.

Illustration 190	g03886246
This illustration is a magnification of Illustration 189. Damage (40) is located in the fillet. DO NOT USE THIS PART AGAIN.

Illustration 191	g03886250
The damage from foreign objects has penetrated the case hardened surface. DO NOT USE THIS PART AGAIN.

Illustration 192	g03886255
The damage from foreign objects on this tooth exists in the fillet. The damage from foreign objects is shown by the arrow. Examine the tip of the gear teeth that are meshing for similar damage. DO NOT USE THIS PART AGAIN.

Illustration 193	g03886258
The tip of the gear teeth that are mating is embedded into the fillet. Do not reuse this gear or the gears that are mating with the broken tooth. Inspect other gears in the drive train for damage. DO NOT USE THIS PART AGAIN.

Illustration 194	g03886262
The face of this tooth is severely cracked. Damage from foreign objects can cause a tooth to crack. DO NOT USE THIS PART AGAIN.

Illustration 195	g03886267
The face of the tooth is severely cracked. The crack is the result of damage from foreign objects. The wide gap that is between each line of stress and the deep ridges indicates that this crack occurred quickly. DO NOT USE THIS PART AGAIN.

Illustration 196	g03886273
The severely cracked tips of teeth are the result of damage from foreign objects. DO NOT USE THIS PART AGAIN.

Illustration 197	g03886278
The deep indentation that is shown on the gear above is from a roller bearing. DO NOT USE THIS PART AGAIN.

Illustration 198	g03886281
This type of damage from foreign objects was caused by soft debris. Usually, soft debris will not cause a significant amount of damage. USE THIS PART AGAIN.

Damage from Foreign Objects

Note: Gears that have damage from the failures of other parts should be inspected closely due to the potential of cracking. Use a dye penetrant to check for cracks in the dents that are on the teeth.

Illustration 199	g03886283
The profile of a gear tooth is shown above. The face of the gear tooth is a critical area that should be inspected for damage. (41) Face of the tooth (42) Root

Illustration 200	g03886288
Bruises are seen on the gear tooth. Although the bruises are visible, the bruises do not leave any indentations on the face of the tooth. USE THIS PART AGAIN. (43) Areas of bruises

Illustration 201	g03886289
Minor damage from foreign objects exists. Use a dye penetrant to check for cracks in the face of the tooth. USE THIS PART AGAIN.

Use the gear again if no cracks are found by using a dye penetrant.

Illustration 202	g03886290
Damage from foreign objects is seen at the pitch line of the tooth. Use a dye penetrant to check for cracks in the face of the tooth. USE THIS PART AGAIN.

Use the gear again if no cracks are found by using a dye penetrant.

Illustration 203	g03886292
Significant damage from foreign objects exists. Use a dye penetrant to check for cracks in the face of the tooth. BORDERLINE

Use the gear again if no cracks are found by using a dye penetrant.

Illustration 204	g03886293
Significant damage from foreign objects exists on the face of the tooth. The dye penetrant detected a crack in the dent. DO NOT USE THIS PART AGAIN.

Illustration 205	g03886294
The damage from foreign objects on this gear has not penetrated the case hardened surface. The area of the root in the fillet is not damaged. Use proper inspection procedures to verify that no cracks are present. BORDERLINE

Illustration 206	g03886296
Severe damage from foreign objects exists on the face of the tooth. The dye penetrant detected cracks in the dents. DO NOT USE THIS PART AGAIN.

Rippling

Illustration 207	g03886300
The gear has damage from rippling that is shown between the lines. This type of damage would be most common on highly loaded gear teeth. DO NOT USE THIS PART AGAIN.

Illustration 208	g03886347
Rippling has advanced from scoring to pitting to a change in the profile. DO NOT USE THIS PART AGAIN.

Lipping

Illustration 209	g03886358
Lipping is the permanent displacement of surface metal. Lipping will happen if a gear is too soft. Lipping will happen if a gear is overloaded during adequate lubrication. If the lubrication was not adequate, the damage would be a combination of scoring, metal pullout, and smearing. DO NOT USE THIS PART AGAIN.

Gear Bores

Bores of gears in drive trains are sensitive to damage. If the gear will be reused, the bore must not have any wear or damage. A good light source is required to inspect fully the bore of a gear.

Refer to"Prepare the Area for Inspection" to clean the bore of the gear. If the gear bore has stains that cannot be removed with 8T-7765 Surface Reconditioning Pad and solvent, do not reuse the gear. A gear with minimal damage to the bore can be reused. Make a careful decision on reusing any gear bore because gear bores are sensitive to damage. If a gear bore has more than one type of damage, the gear bore should not be reused. Gears with lightly damaged gear bores may be reused if each of the following conditions are true:

• The case hardened surface has not been penetrated.

• Damage is light.

• Damage is not located in the areas of contact of antifriction bearings.

• Damage does not extend across more than 25% of the width of the thrust face.

• There are not many damaged areas.

• Damage can be smoothed with a 6V-2010 Polishing Stone.

Planetary Gear Bores

Planetary gear bores are unique to other gear bores in drive trains. Planetary gears are highly loaded. It is important to inspect carefully all planetary gear bores.

Illustration 210	g03886369
This bore is in excellent condition and there is no visible damage. USE THIS PART AGAIN.

Illustration 211	g03886374
If a gear bore is used as a race for a bearing, the bore should not be worn or damaged. There is no wear or damage in this gear bore. USE THIS PART AGAIN.

Illustration 212	g03886379
Foreign objects have damaged the bore of this planetary gear. DO NOT USE THIS PART AGAIN.

Illustration 213	g03886388
Examine both edges of the gear. Notice that the nick is NOT on the bearing surface and has NOT penetrated the case hardening. Use a 6V-2010 Polishing Stone and oil to remove the sharp edges around nick (1) before reusing this gear. USE THIS PART AGAIN.

Illustration 214	g03886393
If a bore has stains, clean the bore of the gear. Refer to "Prepare the Area for Inspection" for more information. If the gear bore is cleaned and there are still instances of pitting, do not reuse the gear. The standard cleaning procedures were applied to the bore of the gear in this illustration. The discolored lines were not removed. The discolored lines inside this gear bore are instances of pitting. DO NOT USE THIS PART AGAIN.

Illustration 215	g03886405
The stains could not be removed from the bore of the gear. The stains are instances of pitting. DO NOT USE THIS PART AGAIN.

Illustration 216	g03886408
This gear bore has been damaged in both the area of bearing roller track (2) and the area of retaining washers (3). DO NOT USE THIS PART AGAIN.

Illustration 217	g03886410
Use good lighting for inspection of any gear bore. If the surface of the bore has an irregular contour, the beams of light will not be straight. DO NOT USE THIS PART AGAIN.

Illustration 218	g03886415
The washers for retaining bearings have spun inside the gear bore. DO NOT USE THIS PART AGAIN.

Illustration 219	g03886421
Brinelling will create a hilly appearance and a hilly texture on the surface of the bore. Do not reuse a gear with a bore that has damage from brinelling. DO NOT USE THIS PART AGAIN.

Illustration 220	g03886426
This gear bore has corroded. Notice that the corrosion makes a pattern of parallel bands in the bore. DO NOT USE THIS PART AGAIN.

Illustration 221	g03886429
The bore on this planetary gear has spalled. Check lube quality, loading, parts alignment. DO NOT USE THIS PART AGAIN.

Illustration 222	g03886434
The gear bore that is shown in the above illustration has corroded. DO NOT USE THIS PART AGAIN.

Gears with Replaceable Bearing Races

Damage to a bore with a replaceable bearing race occurs when the bearing cup rotates inside the gear bore. Planetary gears with replaceable bearing races can often be used again if the race has only crept in the bore. Before reusing the gear, check the size of the gear bore to determine that the bore is still within specifications for reusability. Refer to Reuse and Salvage Guideline, SEBF8185, "Salvage Procedure for Final Drive Planet Gear Used in Off-Highway Trucks" for more information about gears that have replaceable bearing races.

Illustration 223	g03886437
The bearing race has crept inside this bore and the race has caused only a small amount of damage. If the bore is still within the specifications, the gear may be used again. The dark brown or black appearance may be caused from gear oil and the appearance can be removed with 8T-7765 Surface Reconditioning Pad and solvent. If the bore is not within tolerance, refer to Reuse and Salvage Guideline, SEBF8185, "Salvage Procedure for Final Drive Planet Gear Used in Off-Highway Trucks" before installing the new bearing. USE THIS PART AGAIN.

Illustration 224	g03886439
The bearing race that was in this gear has spun inside the gear bore. If a gear bore is blue, do not reuse the gear. The blue color in the bore was caused by extreme temperatures. If a gear bore becomes overheated, the gear cannot be used again. DO NOT USE THIS PART AGAIN.

Spider Gear Bores

Illustration 225	g03886445
The bore of this gear has spun around a shaft. The bore is beyond the limit for reusing. The teeth are also heavily damaged. DO NOT USE THIS PART AGAIN.

Splines

Splines should be checked for wear with a seal pick. The seal pick should be held perpendicular to the spline. If the pick is stopped by any of the wear steps, do not reuse the gear. Visually check for other damage on the spline before reusing the gear. Refer to the Inspecting the Splines section within Reuse and Salvage Guideline, SEBF8443 for proper Inspection and Measuring procedures.

Illustration 226	g03886448
Use a seal pick to determine if a spline can be reused. Hold the pick in a position that is perpendicular to the spline tooth that is being checked. Drag the seal pick across wear step (5). If the pick is stopped by the wear step, do not reuse the spline. Fillet radius (6) is also shown. DO NOT USE THIS PART AGAIN. (4) Seal pick (5) Wear step (6) Fillet radius

Illustration 227	g03886455
This gear has spline wear that does not stop a seal pick. Check the wear at the ends of the contact between the shaft and the gear bore. If there is no other damage, the spline may be used again. USE THIS PART AGAIN.

Thrust Faces

The thrust face of a planet gear, sun gear, or side gear should not have smears or heat checks. Heat checks are shallow cracks that interrupt the film of lubrication. Heat checks can shave off material from the thrust bearing. Gears with light damage on the thrust face can be used again. Light scratches are acceptable only when the scratches do not stop a seal pick. If there is a sharp edge on the thrust face, remove the edge with 6V-2010 Polishing Stone and oil.

Illustration 228	g03886459
The thrust face on this planet gear is in good condition. The gear may be used again if there are no cracks in the surface of the thrust face. Inspect the gear for cracks with any of the methods for inspecting cracks. USE THIS PART AGAIN.

Illustration 229	g03886462
The differential side gear is approaching the wear limit. This gear does not have any other damage so this gear may be used again. The roughness and damage that is shown by the arrows is the limit for reusability. USE THIS PART AGAIN.

Illustration 230	g03886467
The arrows show the roughness and damage. The complete thrust face does not meet the standards for reusability. Also note the discoloration. DO NOT USE THIS PART AGAIN.