Procedure to Update the 797 and 797B Off-Highway Truck Center Arm Assembly{4305} Caterpillar

Off-Highway Truck:

797 (S/N: 5YW1-UP)

797B (S/N: JSM1-UP)

Introduction

This Special Instruction contains general information and procedures for updating to the current steering arm design of the machines that are listed above.

Read the entire special instruction. Understand the information before you perform any procedures. Understand the information before you order any parts.

When you need to remove components in order to repair the chassis, refer to the appropriate Disassembly and Assembly Manual.

Safety

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Personal injury or death can result from improper lifting or blocking. When a hoist or jack is used to lift any part or component, stand clear of the area. Be sure the hoist or jack has the correct capacity to lift a component. Install blocks or stands before performance of any work under a heavy component. Approximate weights of the components are shown. Clean all surfaces where parts are to be installed.

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Personal injury can result from the sudden release of high pressure oil. Be sure the engine has been shut off for a minimum of five minutes to ensure that the accumulator pressure is zero. The accumulator is filled with dry nitrogen. Do not loosen or remove the valve or the cap from the top of the accumulator.

Note: All torques are standard torque unless the torque is specified.

Required Tooling

Note: For information on fabrication of field tools, contact the dealer service tools at the following address.

Required Parts

Preparing the Area for Welding

Clean the area that will be welded. Make sure that the substances that follow are removed from the area that will be welded.

• Oil

• Grease

• Paint

• Dirt

If the temperature of the base metal is below 0 °C (32 °F), heat the base metal to a temperature of at least 21 °C (70 °F). Maintain the temperature of the base metal at 21 °C (70 °F) during the welding process.

Note: Heat distortion of the base metal is possible when you weld. Avoid excessive heating of the base metal.

Attach the welding ground cable directly to the base metal. Protect machined surfaces from sparks. Protect the machined surfaces from the weld splatter.

Weld Specifications and Qualifications

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Protect yourself and others; read and understand this warning. Fumes and gases can be dangerous to your health. Ultraviolet rays from the weld arc can injure eyes and burn skin. Electric shock can kill. Read and understand the manufacturer's instruction and your employer's safety practices. Keep your head out of the fumes. Use ventilation, exhaust at the arc, or both, to keep fumes and gases from your breathing zone and the general area. Wear correct eye, ear and body protection. Do not touch live electric parts. Refer to the American National Standard Z49.1, "Safety in Welding and Cutting" published by the American Welding Society, 2501 N.W. 7th Street, Miami, Florida 33125: OSHA Safety and Health Standards, 29 CFR 1910, available from U.S. Dept. of Labor, Washington D.C. 20210.

Note: Personal breathing protection should be worn by the personnel that are welding. Personal breathing protection will prevent fumes from entering the lungs of the person that is welding. Use a 1U-8088 Type H Respirator for breathing protection.

Qualifications

Welders must be qualified for fillet welding and groove welding. The welders should be qualified in the use of the welding processes that follow: Shielded Metal Arc Welding (SMAW), Flux Cored Arc Welding (FCAW) and Gas Metal Arc Welding (GMAW). Refer to "American National Standards Institute (ANSI)/American Welding Society (AWS) Specification D1.1, or Specification D14.3" for information that regards the qualifications for the processes that follow: SMAW process, FCAW process and GMAW process. The welders must have used the process at some time within the last six months. The welders must complete the process of certification if the welders have not used the welding processes for six months.

Note: For further information, see Special Instruction, REHS1841, "General Welding Procedures".

Proper Welding Procedure on Machines and Engines with Electronic Controls

Proper precautions are necessary to prevent damage to electronic controls. When you weld on a machine with electronic controls, use the steps that follow:

1. Turn off the engine. Put the key start switch in the OFF position.

2. If the machine has a battery disconnect switch, open the switch. If the machine does not have a battery disconnect switch, disconnect the negative battery cable at the battery.

3. Connect the ground cable for the welder directly to the actual machine component that will be welded. Attach the clamp for the ground cable as close as possible to the area that is being welded. This will reduce the chance of damage from welding current to the components that follow: bearings, hydraulic components and electrical components.

   Note: Do NOT use electrical components as a ground point for the welder. Do NOT use ground points for electronic components as a ground point for the welder.

4. Protect the wiring harnesses from the weld splatter.

Specifications

Low Hydrogen Electrodes for the SMAW Process

The tables that follow list the mechanical properties of welds that are deposited by low hydrogen electrodes.

Low hydrogen electrodes must be stored in an electrode oven at 120 °C (248 °F). If low hydrogen electrodes get damp, scrap the low hydrogen electrodes or recondition the low hydrogen electrodes to the manufacturer's specifications.

The table that follows shows setting for the welding current for the electrode diameter.

Use a polarity setting of DC reverse polarity. Remove the slag after each pass of the welding electrode. The width of the weld should not exceed two times the electrode diameter.

Flux Cored Welding Electrode for the FCAW Process

As an alternative process, use the Flux Cored Arc Welding (FCAW) with E71T-1 H8 (ANSI/A5.20) welding electrode and the manufacturer's shielding gases that are specified for inside welding. The H8 implies that the electrode is designed to provide less than 8 ml/100 g of diffusible hydrogen in the weld deposit. The weld that is deposited by the flux cored welding electrode will have the following minimum mechanical properties:

The table that follows lists the mechanical properties of welds that are deposited by the flux cored welding electrode.

The table that follows shows setting for the welding current for the flux cored welding electrode that has a diameter of 1.3 mm (.051 inch).

Note: The settings for the welding current can vary due to the position of the weld. Also, the settings for the welding current can vary with the manufacturer of the welding electrode.

Use a polarity setting of DC reverse polarity. Remove the slag after each pass of the welding electrode. The fast freezing characteristics of flux cored welding electrode increases the possibility of evolving gas that is trapped in the weld. Control the size of the weld in order to reduce the possibility of evolving gas that is trapped in the weld. The volume of the fillet weld should not exceed 8.0 mm (.315 inch).

Arc Welding Electrodes for the GMAW Process

The table that follows lists the mechanical properties of welds that are deposited by the GMAW Process.

The welding parameters will vary with the position of the weld and with different electrode manufacturers.

Weld Inspection

The weld should not have any of the conditions that follow:

• Cracks

• Porosity

• Undercut

• Incomplete Fusion

In order to verify the quality of the weld, refer to "American National Standards Institute (ANSI)/American Welding Society (AWS) Specification D14.3".

Welding on Engines and Machines with Electronic Controls

Proper welding procedures are necessary in order to avoid damage to the electronic controls and to the bearings. The following steps should be followed in order to weld on a machine or an engine with electronic controls.

1. Turn off the engine. Place the engine start switch in the OFF position.

2. If equipped, turn the battery disconnect switch to the OFF position. If there is no battery disconnect switch, remove the negative battery cable at the battery.

3. Disconnect the J1/P1 and J2/P2 connectors from the ECM. Move the harness to a position that will not allow the harness to accidentally move back and make contact with any of the ECM pins.

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Illustration 1	g01347582
Use the example above. The current flow from the welder to the ground clamp of the welder will not cause damage to any associated components. (A) Engine (B) Welding rod (C) Keyswitch in the OFF position (D) Battery disconnect switch in the open position (E) Disconnected battery cables (F) Battery (G) Electrical/Electronic component (8) Maximum distance between the component that is being welded and any electrical/electronic component (J) The component that is being welded (K) Current path of the welder (L) Ground clamp for the welder

4. Clamp the ground cable from the welder to the component that will be welded. Place the clamp as close as possible to the weld. Make sure that the electrical path from the ground cable to the component does not go through any bearing. Use this procedure in order to reduce the possibility of damage to the following components:
   • Bearings of the drive train

   • Hydraulic components

   • Electrical components

   • Other components of the machine

   Note: If electrical/electronic components are used as a ground for the welder, or electrical/electronic components are located between the welder ground and the weld, current flow from the welder could severely damage the component.

5. Protect any wiring harnesses from the debris which is created from welding. Protect any wiring harnesses from the splatter which is created from welding.

6. Use standard welding procedures in order to weld the materials together.

Rework Procedure

1. Move the machine to level hard ground. Securely chock the wheels. Engage the parking brake.

2. Remove the hoses from the steering links.

3. Remove the steering links from the center arm assembly. The weight of each steering link is 195 kg (430 lb). Refer to Disassembly and Assembly, RENR2588, "Steering Links - Remove". Save the steering links in order to be reused later.

4. Remove the hoses from the center arm assembly. Save the hardware in order to be reused later.

5. Use tooling (A) in order to remove the center arm assembly. The weight of the center arm assembly is 222 kg (490 lb). Refer to Disassembly and Assembly, RENR2588, "Center Arm (Steering) - Remove and Install". Discard the center arm assembly.

6. Remove the upper bearing and the lower bearing for the steering box. Discard the bearings.

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Illustration 2	g01382208
Bottom view (A) 95.26 ± 0.03 mm (3.750 ± 0.001 inch) Ø, 2 holes in line, surface finish of F, true position to centerline at maximum material of 0.08 mm (0.003 inch) (B) 176.0 ± 0.8 mm (6.93 ± 0.03 inch) Ø spot face, three places, surface finish of K (C) 166.0 ± 0.5 mm (6.54 ± 0.02 inch), perpendicular to bores (A) within 0.13 mm (0.005 inch) (D) 3 ± 1 mm (0.10 ± 0.04 inch) X 45 degree chamfer, two places (E) 1.6 ± 0.8 mm (0.06 ± 0.03 inch) radius

7. The bores must be checked in order to ensure that the bores are within specified dimensions. If the bores are not to specified dimensions, the bores must be welded and remachined prior to the installation of the grease ports.

8. The distance between the flat surfaces must be checked in order to ensure that the surfaces are parallel. The distance between the flat surfaces must be checked in order to ensure that the surfaces are to specified dimensions. The flat surfaces must be checked in order to ensure that the surfaces are perpendicular to the center line of the bore. If the flat surfaces are not to specified dimensions, the flat surfaces must be welded and remachined prior to the installation of the grease ports.

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Illustration 3	g01382867
(F) 2 holes 8.6 mm Ø Thru, 1/8-27 NPTF-A by 15 mm (0.6 inch) deep (G) 34.0 ± 0.5 mm (1.34 ± 0.02 inch)

9. Use Tooling (C) in order to thru drill the hole and tap the hole to depth in the upper bore for the center pivot pin of the steering box. Use Tooling (C) in order to thru drill hole and tap hole to depth in the lower bore for the center pivot pin of the steering box. Refer to Illustration 3.

   Note: Recommended drill speed for this material is a maximum of 800 rpm. Drill bit should be fed into the hole at a rate of 0.3 mm/revolution (0.01 inch/revolution).

   Note: Tooling is available for loan to aid in drilling the new tapped holes (A). For information on obtaining tooling contact MT&S Product Support, at Hays_Doug_E@cat.com. Required information is your name, your shipping address, and your phone number.

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Illustration 4	g01382871
Top view (H) 134.5 ± 5 mm (5.3 ± 0.2 inch) (J) 110 ± 5 mm (4.3 ± 0.2 inch) (K) 109.1 ± 5 mm (4.3 ± 0.2 inch) (L) 375 ± 5 mm (14.8 ± 0.2 inch) (M) 369 ± 5 mm (14.5 ± 0.2 inch)

10. Use weld (W1) to weld two bosses (1) to the steering box. Use weld (W2) to weld block (2) to the steering box. Refer to Illustration 4 and Table 9.
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    Table 9

    Weld Tolerances
    Weld	Description
    W1	3 mm (0.12 inch) Fillet weld all around
    W2	4 mm (0.16 inch) Fillet weld both sides

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Illustration 5	g01382874
(N) 552 ± 5 mm (21.7 ± 0.2 inch) (P) 308 ± 5 mm (12.1 ± 0.2 inch) (Q) 99 ± 5 mm (3.9 ± 0.2 inch)

11. Use weld (W3) to weld two bosses (1) to the steering box. Refer to Illustration 5 and Table 10.
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    Table 10

    Weld Tolerances
    Weld	Description
    W3	3 mm (0.12 inch) fillet weld all around

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Illustration 6	g01340120

12. Install two bearings (8A) into the bores of the steering box. Apply Tooling (B) to bearing bores and faces.

13. Install two bearings (8B) into the bore of center arm assembly (10). Apply Tooling (B) to bearing bores and faces.

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Illustration 7	g01382648

14. Install two elbows (16) and two O-rings (17) to block (9) .

15. Install block (9) with three bolts (14) and two O-ring seals (15) to the center arm assembly (10) .

16. Position center arm assembly (10) into the steering box. Position the bore of center arm assembly (10) in order to line up with the bores in the steering box. The weight of the center arm assembly is 220 kg (485 lb).

17. Use Tooling (A) in order to support center arm assembly (10) .

18. Lubricate the bore of center arm assembly (10) with Tooling (B). Install shims (7A) on top of center arm assembly (10) in order to fill the gap between the faces of upper bearings (8A) and (8B). Refer to Illustration 6.

19. Install bottom plate (4) to pin (3) with four washers (5) and four bolts (6). Refer to Illustration 6.

20. Lubricate two shims (7B) with Tooling (B). Install two shims on pin (3). The shims should rest on bottom plate (4). Refer to Illustration 6.

21. Lubricate pin (3) with Tooling (B). Install the pin into the bores from the bottom. Refer to Illustration 6.

22. Install pin (3). Measure the exposed length of the pin on the top of the steering box. Lubricate the shims (7C) with Tooling (B) and install a sufficient quantity of the shims in order to achieve an end play of 3 mm (0.12 inch). Refer to Illustration 6.

23. Install plate (11) with two bolts (12) and two hard washers (13). Refer to Illustration 6.

24. Install plate (4) to the top of pin (3) with four bolts (6) and four hard washers (5). Refer to Illustration 6.

25. Reinstall the steering links from the center arm assembly. The weight of each steering link is 195 kg (430 lb). Refer to Disassembly and Assembly, RENR2588, "Steering Links - Install".

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Illustration 8	g01382896

26. On the right hand side of the truck, disconnect hose (K), hose (L), and hose (M) .

27. Remove bolts (C) and hard washers (D) and remove plate (B) and rear valve group (A) .

28. Remove four nuts (F), four bolts (G) and four hard washers (H) from plate (B) and rear valve group (A). Save bolts (G), hard washers (H), and nuts (F) in order to be reused later. Discard the plate (B) .

29. Remove plug (E) from rear valve group (A). Save plug (E) in order to be reused later.

30. Remove valve (A) from nipple (J) and the remaining valve group. Discard rear valve group (A) .

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Illustration 9	g01382985

31. Remove clip (M) from hose (Q) and hose (R). Save clip (M) in order to be reused later.

32. Remove hose (K), hose (L), and hose (M). Discard hose (K), hose (L), and hose (M) .

33. Rotate clip (S) 180 degrees and secure the clip.

34. Turn clip (N) over and secure clip.

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Illustration 10	g01382199

35. Install valve group (18) to the existing valve group and nipple (J) that are removed in Step 30.

36. Install plug (E) that was removed in Step 29 to valve group (18) .

37. Install valve group (18) to plate (19) with four bolts (G), four hard washers (H), and four nuts (F) that are removed in Step 28.

38. Install plate (19) and valve (18) to the frame with four bolts (C) and four hard washers (D) that are removed in Step 26.

39. On the right hand side of the truck, make the following connections to valve group (18) :

    1. Hose (20) lubricates the right hand steering cylinder pin.

    2. Hose (21) lubricates the lower bearing for the center arm assembly.

    3. Hose (22) lubricates the bearing for the right hand ball stud of the center arm assembly.

    4. Hose (23) lubricates the upper bearing in the steering box.

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Illustration 11	g01382201

40. Route hose (20), hose (21), and hose (22) through existing clips on the right hand side of machine where hose (K), hose (L), and hose (M) that are removed.

41. Route hose (23) parallel to hose (20), hose (21), and hose (22) on right side and secure to existing bolts and hard washers with three clips (25) .

42. Install a clip (24) to hose (23), hose (Q), and hose (R). Secure clip (24) and hoses to clip (N) .

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Illustration 12	g01382198

43. Install two elbows (26) with two O-ring seals (15) into the new threaded holes (F). For the location of holes (F), see Illustration 3.

44. Install hose (23) to elbow (26) for the lower bearing in the steering box.

45. Install two clips (25), two bolts (27), and two hard washers (28) in order to secure hose (23) .

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Illustration 13	g01382923

46. On the left hand side of the truck, disconnect hose (AC), hose (AD), and hose (AE) .

47. Remove bolts (V) and hard washers (W) and remove plate (U) and rear valve group (T) .

48. Remove four nuts (X), four bolts (Y) and four hard washers (Z) from plate (U) and rear valve group (T). Save bolts (Y), hard washers (Z), and nuts (X) in order to be reused later. Discard the plate (U) .

49. Remove plug (AB) from rear valve group (T). Save plug (AB) in order to be reused later.

50. Remove valve (T) from nipple (AA) and the remaining valve group. Discard rear valve group (T) .

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Illustration 14	g01382987

51. Remove clip (AF) from hose (AH) and hose (AJ). Save clip (AF) in order to be reused later.

52. Remove hose (AC), hose (AD), and hose (AE). Discard hose (AC), hose (AD), and hose (AE) .

53. Rotate clip (AK) 180 degrees and secure the clip.

54. Turn clip (AG) over and secure clip.

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Illustration 15	g01382203

55. Install valve group (18) to the existing valve group and nipple (AA) that are removed in Step 50.

56. Reinstall plug (AB) that was removed in Step 49 to valve group (18) .

57. Install valve group (18) to plate (19) with four bolts (X), four hard washers (Z), and four nuts (X) that are removed in Step 48.

58. Install plate (19) and valve (18) to the frame with four bolts (T) and four hard washers (W) that are removed in Step 46.

59. On the left hand side of the truck, make the following connections to valve group (18) :

    1. Hose (20) lubricates the left hand steering cylinder pin.

    2. Hose (22) lubricates the left hand ball stud of the center arm assembly.

    3. Hose (23) lubricates the lower bearing in the steering box.

    4. Hose (21) lubricates the upper bearing for the center arm assembly.

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Illustration 16	g01382206

60. Route hose (21), hose (22), and hose (23) through existing clips on the left hand side of machine where hose (AC), hose (AD), and hose (AE) that are removed.

61. Route hose (23) parallel to hose (20), hose (21), and hose (22) on left side and secure to existing bolts and hard washers with two clips (25) .

62. Install a clip (24) to hose (23), hose (AH), and hose (AJ). Secure clip (24) and hoses to clip (AG) .

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Illustration 17	g01382619

63. Install hose (23) to elbow (26) for the upper bearing in the steering box.

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Illustration 18	g01382202

64. Route hose (20), hose (21), and hose (22) across the right hand side of the steering box.

65. Install hose (20) to the right hand steering cylinder pin.

66. Install hose (21) to the lower bearing for the center arm assembly.

67. Install hose (22) to the right hand ball stud of the center arm assembly.

68. Install clip (P) that was removed in Step 31 to hose (21) and hose (22) .

69. Install clip (25) to hose (23) .

70. Secure clip (P) and clip (25) with bolt (27) and hard washer (28) .

71. Route hose (21) and hose (22) across the left hand side of the steering box.

72. Install hose (20) to the left hand steering cylinder pin.

73. Install hose (21) to the upper bearing for the center arm assembly.

74. Install hose (22) to the left hand ball stud of the center arm assembly.

75. Install clip (AF) that was removed in Step 51 to hose (22) and hose (21) .

76. Secure clip (AF) with bolt (27) and hard washer (28) .

77. Install plate (31) with two bolts (27) and two hard washers (28) .

78. Route two hoses (21) and two hoses (22) along center arm assembly (10) .

79. Install a clip (32) to each pair of hoses (21) and (22) .

80. Secure the clips (32) to plate (31) with bolt (29), two hard washers (28) and a nut (30) .

81. Secure two hoses (21) to the left had side of center arm assembly (10) with bolt (27), hard washer (28), and clip (32) .

82. Install a clip (25) to each of the two hoses (21) .

83. Secure the clips (25) together with bolt (29), two hard washers (28), and nut (30) .

84. Secure the two hoses (22) to center arm assembly (10) with the hardware that was removed in Step 4.