Installing Tapered Roller Bearings in 6G-6352 Planet Gears in Final Drives of Off-Highway Trucks{0760, 0761, 4050, 4055, 7551} Caterpillar

Off-Highway Truck/Tractor:

784B (S/N: 5RK1-UP)

784C (S/N: 2PZ1-UP)

785 (S/N: 8GB1-UP)

785B (S/N: 6HK1-UP)

785C (S/N: 1HW1-UP; APX1-UP; 5AZ1-UP)

785D (S/N: DMC1-UP; MSY1-UP)

785G (S/N: RTL1-UP)

789 (S/N: 9ZC1-UP)

789B (S/N: 7EK1-UP)

789C (S/N: 2BW1-UP)

Introduction

© 2013 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.

This Reuse and Salvage Guideline contains the necessary information in order to allow a dealer to establish a parts reusability program. Reuse and salvage information enables Caterpillar dealers and customers to benefit from cost reductions. Every effort has been made in order 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 questions or additional information concerning this guideline, submit a form for feedback in the Service Information System. In order to address an urgent issue, use the following resources in order to communicate your request to Caterpillar Repair Process Engineering:

• Caterpillar Dealer Technical Communicator

• Dealer Solution Network

• Caterpillar Technical Representative

• Knowledge Network

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

Follow all safety warnings. Most accidents that involve product operation, maintenance, or repair are caused by failure to observe safety warnings. An accident can often be avoided by recognizing potentially hazardous situations before an accident occurs. Personnel must be properly trained in order to perform maintenance, repair, or operate any machine. Safety precautions and warnings are provided this instruction and on Caterpillar products. These warnings should be observed before performing any procedures. Caterpillar cannot anticipate every possible circumstance that might involve a potential hazard. The warnings in this publication and on the product are not all inclusive.

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 in Illustration 2.

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. Caterpillar dealers can supply the most current information.

Installing Tapered Roller Bearings in 6G-6352 Planet Gears in Final Drives of Off-Highway Trucks

Summary

An engineering change in the final drive planet gears uses a tapered roller bearing design. Former 6G-6352 Planet Gears can be reworked to accept tapered roller bearings or a new 8X-6830 Planet Gear can be used as a direct replacement.

The change to tapered roller bearings will provide improved life of the second reduction in the final drive. This Guideline provides a procedure and specifications to rework former gears to the new engineering specifications.

Final drive gears that meet the reuse/salvage specifications can be expected to perform normally in the same application until the next overhaul. Never install a part that this Guideline indicates cannot be used again. Before installing a used or reconditioned part, correct and condition that may cause wear or misalignment to the gear.

References

Tooling and Equipment

Cleaning

Before any gear is visually inspected, clean the gear thoroughly following these guidelines.

• When lifting or moving parts to be cleaned, use proper lifting devices for operator safety and to prevent machined surfaces from being damaged.

• Wash each gear separately. When several parts are washed together, machined surfaces can be damaged.

• Use compressed air to dry the gears.

• If inspection is not done immediately after cleaning, put hydraulic oil on each machined surface to prevent rust or corrosion. Then place the parts into a clean container.

Visual Inspection

Before machining any gear to accept roller bearings, first visually inspect the gear for damage caused by rolling/sliding movement. Also check for damage such as scoring, pitting, cracking, spalling, or other damage that would not allow the gear to be used again.

Rolling or Sliding Damage

When two mating gears rotate, the teeth go through a combined rolling/sliding movement. This action occurs during contact above and below the pitch line at all points. Only at the pitch line is there rolling action alone. Refer to Illustration 3.

Illustration 3	g02173883
Rolling/sliding action of gears during normal operation. (1) Driven gear (2) Driving gear (3) Beginning of tooth contact with rolling and sliding action (4) Operating pitch line contact with rolling action (5) End of tooth contact with rolling and sliding action

Scoring

The sliding action that normally occurs, while the gear is under load, is the basic cause of surface damage, such as scoring. The sliding action is greatest near the tip and root of the tooth. Inspect these areas carefully for scoring and other types of surface damage.

Pitting

Sliding under load can also cause pitting (sliding contact stress fatigue). The areas of greatest stress caused by sliding are the highest and lowest points of single tooth contact on the driven gear. Inspect these areas carefully for pitting. Pitting occurs more often on the dedendum of the gear tooth below the pitch line.

Spalling

Rolling action can also produce sub surface cracks that can lead to spalling (often referred to as case crushing).

Gear Tooth

It is very important to accurately inspect final drive gears because the gears experience high stress loads. If an unacceptable gear is used again, it will be more likely to fail. An unacceptable gear can cause damage to the entire final drive system, resulting in downtime, and higher operational costs.

Determine if the gears can be salvaged using Reuse and Salvage Guidelines, SEBF8193, "Reusability of Drive Train Gears" as a guide. Look closely for defects such as cracking, pitting, spalling, surface damage, excessive wear, or extreme heat distortion. Inspect every tooth of each gear, because it is possible for only one gear out of the set to be damaged.

Gear inspection can be done using a magnifying glass, magnetic particle, or dye penetrant to distinguish between small scratches and cracks. If the gear meets all the reusable guidelines, it can be salvaged using the procedure in the Guideline.

Inside and Outside Diameters

Illustration 4	g02173967

1. Use an inside micrometer to measure the inside diameter of the bore. Take a measurement in three places (A, B, and C) at 60° intervals. If the inside bore diameter is larger than 149.862 mm (5.9000 inch), the gear should not be used again.

Show/hide table



Illustration 5	g02173974

2. Use an outside micrometer to obtain the measurement-over-pins diameter using two 17.4625 mm (0.68750 inch)diameter pins located at 180° apart from each other. Take three measurements (A, B, and C) at 60° intervals. The measurements should not be less than 251.197 mm (9.8896 inch).

3. If the requirements in Steps 1 and 2 are not met, the gear cannot be used again.

Machining Specifications

Machine the bore of 6G-6352 Planet Gears to the specifications in Table A. Refer to Illustration 6 for item identification.

Illustration 6	g02174017
Dimensions to rework a 6G-6352 Planet Gear for tapered roller bearings.

Salvage Procedure

1. Clean, inspect, and check to make sure that the gear meets all the reusability guidelines in Guideline for Reusable Parts, SEBF8193 and this Guideline

Show/hide table

NOTICE
Do not use hardened jaws on gears with hardened teeth. These jaws may cause the gear tooth to fracture or chip.

2. Chuck the gear into the lathe. Use soft jaws in the chuck due to the hardness of the gear teeth.

3. Use two dial indicators to align the face of the gear and center the inside bore diameter. The bore must be centered to within ± 0.013 mm (± 0.0005 inch).

Show/hide table



Illustration 7	g02174022
Use two indicators to locate the face and center of the gear.

4. Using a boring bar and ceramic insert, machine the bore to the finished diameter. Make sure that the machining and surface tolerances are not exceeded.

Show/hide table



Illustration 8	g02174030
Machine the gear bore to the finished diameter.

5. Cut the snap ring groove into the bore. Refer to Table A and 6 for dimensions and location.

6. Remove the gear from the lathe and check all dimensions. Inspect the gear teeth for any possible tooth fracturing caused by the machining operation.

7. Refer to the Service Manual and Parts Book for Installation procedures and part numbers.