After Product Support Program For Repairing The Rear Engine Mounts In Certain 793, 793B, And 793C Trucks Caterpillar

After Product Support Program For Repairing The Rear Engine Mounts In Certain 793, 793B, And 793C Trucks

Usage:

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Caterpillar: Confidential Yellow

NOTE: This Program can only be administered after a failure occurs. The decision whether to apply the Program is made by the dealer. When reporting the repair, use "PS5288" as the Part Number and "7755" as the Group Number. Use "96" as the Warranty Claim Description Code and use "Z" as the SIMS Description Code.

NOTE: It is recommended that this program be implemented during Planned Component Rebuild when the engine is out. No labor is allowed to remove and install the engine.

NOTE: Inspection of cracks and approval by product support representative is required before implementing this program.

Termination Date

June 30, 2000

Problem

The rear engine mounts may crack in certain 793, 793B, and 793C Trucks.

Affected Product
Model & Identification Number

793 (3SJ1-Up)

793B (1HL1-Up)

793C (4AR77-148, 4AR150-158)

NOTE: Inspection of cracks and approval by product support representative is required before implementing this program.

Parts Needed

1 - 1352578 Support-LH

1 - 1387460 Support-RH

Action Required

See the attached procedure.

Service Claim Allowances

NOTE: This is a 95-hour job total to rework both sides including the time required to fabricate the plates. A maximum of $150.00 will be allowed for material to fabricate the plates. Both sides must be reworked at the same time. No time will be allowed to remove and install the engine.

NOTE: A one time allowance not to exceed $10,000.00 will be allowed for labor and materials to fabricate the tooling. Limited to one time per Dealer.

Parts Disposition

Handle the parts in accordance with your Warranty Bulletin on warranty parts handling.

Attach.

(1-Rework Procedure)

Rework Procedure

Retrofit Of Rear Motor Mount Castings

Welding Procedure / Field Repair

The following procedure is written to cover the field replacement of the rear engine mounts on the 793 Off Highway Truck Frame. This procedure explains the steps necessary to reduce cracking and improve the life of the rear motor mount castings.

Welding Procedure

Welding operator personal protection should be provided to assure that total weld fume in the operators breathing zone does not exceed OHSA limits. All repair welding operators must be qualified for groove and fillet welding, as outlined in the current ANSI/AWS D14.3, or Caterpillar Manufacturing Practices MC1000-105 for the SMAW (Shielded Metal Arc Welding) process in all welding positions. The welding operator must also have used this welding process during the last six months or be re-certified for this process before welding. Documentation must be maintained of the weld operators qualifications.

The area to be repaired and the surrounding area must be at a minimum temperature of 16 degrees C (60 ° F)before and during all cutting, carbon arc gouging, and welding. The SMAW process shall be used with E7018 (ANSI/AWS A5.5) welding electrode. The weld deposited by these electrodes will have the following minimum mechanical properties:

500 MPA (72 kSI) Tensile Strength

420 MPA (60 KSI) Yield Strength

22% Elongation in 50mm (2 inches)

27J (20 ft lbs) notch toughness at -29° C (-20° F)

These are low hydrogen electrodes and must be stored in a electrode oven at 121 ° C (250 ° F) when not in use. If the electrodes get damp, scrap or recondition them to manufacturers specifications. The following chart relates to the electrode diameter and approximate current settings for welding:

Use the direct current electrode positive (DC reverse polarity) setting and remove the slag after every pass. The weld pass size shall not exceed two times the electrode diameter.

As an alternative process the FCAW process may be used with E71T-1 (ANSI/AWS A5.20) welding electrode and the manufacturers specified shielding gas(es).The weld deposited by these electrodes will have the following minimum mechanical properties:

500 MPA (72 KSI) tensile strength

420 MPA (60 KSI) yield strength

22% elongation in 50mm (2 inches)

27J (20 ft lbs) notch toughness at -29 deg° C (-20° F)

NOTE: This type of electrode has limitations of it is used to carry larger weld pass volumes in the flat welding position. Due to fast freezing characteristics of this electrode's slag system, there is a chance of trapping evolving gasses in the weld melt. Precaution should be taken by controlling weld pass size.

Welding parameters will vary due to weld position and manufacturer of the welding electrode. Use the direct current electrode positive (DC reverse polarity) setting and remove the slag after every pass. The weld pass size shall not exceed 8mm (0.31") fillet volume.

Repair

This procedure assumes that the engine, front cross member and associated plumbing have been removed.

1. Prepare to set the fabricated tool to the proper rear engine mount height for this individual truck. Attach hoist chains to the fabricated tool in the forward lift eyes provided.

NOTE: The forward lift eyes are used when the fixture is empty.

2. Remove left hand front round locating button from the fabricated tool.

3. Position the fabricated tool down onto the front and rear motor mounts.

4. Secure the fabricated tool (4 bolts per side) to the rear engine mounts.

5. Equalize the fabricated tool between the rear engine mount using the etched lines on the fixture.

6. Secure the two sliding members of the fabricated tool (4 bolts per side) so they can not move.

7. Run the threaded bar knobs down until they just touch the top of the main rail behind the main strut castings.

NOTE: It helps to use a .010 inch feeler gage or a paper card to gage when the bar knob end contacts the main rail. Using a feeler gage guarantees that the fixture has not inadvertently raised while the bar knobs are being set.

8. Secure both lock nuts, against the fixture and one another.

NOTE: This procedure insures that the new rear engine mounts will be located at the same height as the old mounts.

9. Clean the rear motor mount weld area of oil, grease, paint, and dirt.

NOTE: Note the location of all affected blocks, brackets, and bosses.

10. Use a cutting torch to make a rough cut around the outside window area. Make cut line at approximately 1 inch from the inside of the weld all around.

NOTE: Do not cut into the inside reinforcement plates. After cutting outside window remove plate from frame.

11. Cut off and save all hardware attachments from this plate.

12. Reach in this open window and use the interior reinforcement plates for a guide and cut out the inside window plate along with the motor mount.

13. Move hoist chains from the forward lift eyes to the rear lift eyes.

NOTE: The rear lift eyes are used when the fixture is full.

14. Loosen the eight bolts securing the sliding members just slightly.

15. Remove the fixture and old motor mounts.

16. After both window plates are removed prepare the weld joint by carbon arc gouging the existing weld joints.

17. Cut a 30° bevel on the vertical weld seam on the inside of the frame adjacent to the motor mounts.

NOTE: Remove any slag or carbon with a grinder. Make sure weld joints are square and free of any gaps, voids, or rough areas.

18. Locate the new motor mounts to the fabricated tool. Part number 135-2578 is for the left hand rear motor mount and 138-7460 is for the right hand rear motor mount.

19. Reinstall the round locating button on the bottom side of the left front leg of the fabricated tool.

20. Position the fixture and mounts so that the button inserts in the left front engine mount hole, this locates the tool front to rear in the frame.

21. Lower the fabricated tool down until it rests on the front engine mount saddles.

NOTE: The rear of the fabricated tool should rest between the main rails and main front strut castings just behind the welds connecting them. The fixture must rest on at least three points, the two rear points are more critical than the front.

22. Slide the new engine mount casting into the windows as shown in figure 16. Do not over tighten pusher screws.

23. Equalize the scribe lines on the fixture.

24. Tighten the four bolts on each side that secure the sliding details. Maintain slight tension on pusher screws.

25. After the mounts are located, tac weld to left and right side of frame. Examine the weld joint at top and bottom. If there is a 3mm gap or more, back gouge the joint so that complete penetration can be attained.

26. Make a weld pass top and bottom. Before welding the outside vertical seams be sure that there is a minimum root opening of 6mm.

27. After the root pass has been completed all around the mount inside and out, the fixture can be removed.

28. Complete all welds on the motor mount slagging each pass.

29. Locate fabricated window cover plates. Equalize weld joint all around then tack in place. Maintain a minimum root opening of 6mm all around. Weld the vertical seams first. Do not allow vertical welds to enter the j-goove welds on the horizontal weld seams.

30. Complete the horizontal welds. Make sure welds are flush with the rail and not concave.

31. Cut the hardware off of the old motor mounts and window plates.

32. Clean them by grinding and relocate and weld them to frame

NOTE: Any hardware that is on a weld seam or close to the blend line of the rear motor mount casting will have to be relocated 25mm from these points. The left hand rear motor mount and 138-7460 is for the right hand rear motor mount.

Fabrication Needs:

1. Cut a plate 669mm x 612mm from 16mm thick, steel plate. See the following chart. Refer to attach drawing for bevel specifications and dimensions.

The following list indicates approved steel: