Using the 149-4935 Measuring Group on A6, A7, and A8 Rexroth Hydraulic Pump and Motor Groups{0784} Caterpillar

Introduction

This measuring tool group is a combined set of tools for measuring the limit of separation (liftoff dimension) on Rexroth A6 Motors and A7/A8 Pumps. This kit contains all the necessary tools to measure five pump/motor sizes (55, 80, 107, 160, and 200 cc). Each gauge plate is laser engraved with the part number for easy identification. Over 600 disposable gauge balls provide the capability to measure 200 or more pumps before reordering. One, 3/22 inch punch is provided to remove the gauge balls after measurements are taken.

NOTE: 1) Each gauge ball can only be used once. 2) Gauge balls contain lead and must be sent to a certified recycler for disposal. 3) A second set of 107cc and 160cc Gauge Plates are included to expand this kit for use on A8 Pumps.

Illustration 1. 149-4935 Pump and Motor Measuring Group. Refer to Chart A for item identification.

Procedure

Prior to beginning liftoff dimension measurements, be sure the drive group is completely installed and the bearing pre-load is set. The following steps will establish the correct thickness of shim to maintain the correct liftoff limitation. Read and understand all instructions prior to beginning work. In the case of future changes or upgrades, these instructions are for reference purposes only, and the mechanic should follow their specific Disassembly and Assembly Manual Instructions.

Pumps and Motors with Type 1 Barrel

Illustration 2. Type 1 Barrel Assembly.

1. Remove all retaining plate screws, retaining plate, and pistons.

2. Reinstall center pin (2), spring (1), retaining plate (3), and three screws (4) as shown in Illustration 3.

Illustration 3.

(1)Spring

(2) Center Pin.

(3) Retaining Plate.

(4) Screws.

3. Select the correct gauge plate (for pump/motor size to be rebuilt) from the tool group, refer to Charts A or B.

4. Place three 149-5141 Gauge Balls in the "TOP" of the gauge plate (one in each of the three outer holes) as shown in Illustration 4.

Illustration 4. Place Gauge Balls In Holes Indicated By Arrow.

NOTE: Gauge plates have the part number and the word "TOP" engraved on the upper side.

5. To keep the gauge balls from falling out of the gauge plate during installation, press on each one with your thumb or place a small amount of grease in the three tapered holes.

NOTE: Pressing the balls too deeply into the gauge will provide inaccurate measurements.

6. Install the gauge plate assembly into the cylinder barrel with the gauge balls facing away from center pin as shown on Illustration 5. Use a small amount of grease to hold the plate assembly in the cylinder barrel.

Illustration 5. Install Gauge Plate Assembly.

7. Install the cylinder barrel onto the center pin as shown in Illustration 6.

Illustration 6. Install Cylinder Barrel Onto Center Pin.

NOTE: Do not drop the cylinder barrel onto center pin. this will prematurely crush the gauge balls, causing inaccurate measurements.

8. Place valve plate and head group (5) on the drive motor; start all bolts (6) as shown in Illustration 7.

Illustration 7.

(5) Valve Plate And Head Group.

(6) Bolts.

9. Tighten head bolts to the specified torque while turning pump/motor shaft. This process will evenly seat all the pump/motor components.

10. Loosen and remove previously installed head bolts, head group, and valve plate from drive motor.

11. Remove cylinder barrel from drive motor.

12. Remove the gauge plate assembly from cylinder barrel, and carefully wipe off any excess grease from gauge plate assembly.

13. Measure the gauge plate assembly thickness (Z) (gauge plate plus crushed gauge ball) as shown in Illustration 8.

a. Take one measurement at each gauge ball location.

b. Make sure all three values are within ± 0.05 mm (.002 in); if not, punch out crushed gauge balls from back side of gauge plate and repeat procedure starting at Step 4.

Illustration 8. Measure Thickness (Z) Of Gauge Plate.

14. Take the average of the three values and subtract the proper liftoff dimension (see Charts A or B for proper liftoff dimensions). The remaining value is the correct shim thickness that provides the proper liftoff dimension.

Example

* Three crushed gauge ball measurements = 5.01, 5.02, and 5.02 mm (.197, .197, and .198 in), averaged = 5.01 mm (.197 in).

* Liftoff dimension (A6VM160 from Chart A) = 0.25 ± 0.05 mm (.010 ± .002 in).

* Average - liftoff dimension = 5.01 mm -0.25 mm = 4.76 mm (.197 in - .010 in = .187).

* Use a 4.76 ± 0.05 mm (.187 ± .002 in ) shim.

15. Remove three retaining plate screws and retaining plate from drive.

16. Reassemble the pump/motor using the standard specifications and the shim determined in Step 14.

NOTE: Some pump/motor styles do not provide enough room to align the pistons in the barrel from this end. On these styles, the rotating group may need to be completely removed in order to reassemble the pump/motor.

17. Remove and discard the crushed gauge balls from back side of the gauge plate with 1U-7276 Punch.

NOTE: Gauge balls contain lead and must be sent to a certified recycling facility for disposal.

Pumps and Motors with Type 2 Barrel

Illustration 9. Type 2 Barrel Assembly.

1. Remove all retaining plate screws, retaining plate, pistons, center spring, and center pin disk.

2. Reinstall center pin (1), retaining plate (2), and three screws (3) as shown in Illustration 10.

Illustration 10.

(1) Center Pin.

(2) Retaining Plate.

(3) Screws.

3. Set the 149-4934 Gauge Group (centered on middle of spring pin) as shown in Illustration 11.

Illustration 11. Set The Gauge Group.

4. Install gauge group (4) into cylinder barrel with spring washers facing away from center pin as shown in Illustration 12. A screw driver inserted into the top of the cylinder barrel and/or a small amount of grease may be used to hold the gauge group in place.

Illustration 12. Install Gauge Group (4).

5. Install cylinder barrel onto the center pin a shown in Illustration 13.

Illustration 13. Install Cylinder Barrel.

6. Place valve plate and head group (5) on drive motor. Start all bolts (6) as shown in Illustration 14.

Illustration 14.

(5) Install Valve Plate And Head Group

(6) Bolts.

(7) Tighten head bots to the specified torque while turning pump/motor shaft. This process will evenly seat all pump/motor components.

8. Loosen and remove the previously installed head bolts, head group and valve plate from drive motor.

9. Remove the cylinder barrel from the drive motor.

10. Remove gauge group from cylinder barrel, and carefully wipe off excess grease.

11. Remove spring washers and measure gauge assembly dimension (Z) as shown in Illustration 15.

Illustration 15. Measure Thickness (Z) Of Gauge Plate.

12. Calculate the shim thickness.

a. Subtract the proper liftoff dimension (see Charts A or B for values) from dimension (Z).

b. Compare the remaining valve to the thickness of the center pin disc removed in Step 1.

c. The final difference between these two values (if greater than the tolerance listed in charts A or B) needs to be removed from the shim disc to ensure the correct shim thickness and provide the proper liftoff dimension.

Example

* Measured (Z) dimension = 7.00 mm (.276 in).

* Liftoff dimension (A6VM200 from Chart A) = 0.20 ± 0.10 mm (.008 ± .004)

* (Z) dimension - liftoff dimension - Znet [7.00 mm -0.20 mm = 6.80 mm (.280 in = .008 in = .272 in)].

* Measure center pin disk thickness = 6.50 mm (.256 in).

* Znet - center pin disk = [6.80 mm - 6.50 mm = 0.30 mm (.267 in - .256 in = .011 in) shim reduction].

* 0.30 mm (.011 in ) is greater than the 0.10 mm (.004 in ) tolerance listed in Chart A.

* Therefore 0.30 mm (.011 in) should be removed from shim thickness.

13. Remove shim (8) and shim retainer bolt (7) from top of barrel as shown in Illustration 16.

Illustration 16. Remove Retainer Bolt (7) and Shim (8).

14. Measure the shim thickness and subtract the material to be removed (calculated in Step 12). This is the correct shim thickness and will provide the proper liftoff dimension.

15. Grind the shim to the thickness determined in Step 14.

16. Place the newly ground shim and shim retainer bolt in the cylinder barrel. Tighten the bolt to the required specifications.

17. Remove retaining plate screws, center pin, and retaining plate from drive motor.

18. Reassemble the pump/motor using standard specifications and reusing center pin disk.

NOTE: Some pump/motor styles do not provide enough room to align pistons in barrel from this end. On these styles, the rotating group any need to be completely removed in order to reassemble.