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Repair Information - Model 74318 and 74348 Piston Motors
Cleanliness is extremely important when repairing these motors.
Work in a clean area. Before disconnecting the lines, clean port
area of motor. Disconnect hydraulic lines, removing motor
assembly from vehicle and plug ports. Thoroughly clean the
outside of the motor. After cleaning, remove port plugs and
drain oil.
Tools Required for Disassembly and Reassembly
1/2 in. Socket
Ratchet Wrench
Torque Wrench, 68 N•m [50 lbs. ft.]
Soft Face Hammer
Internal Retaining Ring Pliers
(Straight 2.3mm[.090 in.] Tip)
External Retaining Ring Pliers
(Straight 1.8mm[.070 in.] Tip)
Seal Driver or Similar Tool
Petroleum Jelly (Such as Vaseline)
Disassembly
1
Clamp the drive shaft end of the piston motor in a protected
jaw vise with the cap screws up. Remove the six cap screws (28,
or 28A and 28B) from the motor assembly.
2
Use a mallet and tap the backplate (24) to loosen and
remove from housing.
3
Remove valve plate (22) and O-ring (23) from backplate. It
is not necessary to remove roll pins in backplate.
4
Remove motor from vise and remove rotating assembly
(12) from motor housing.
5
If pistons (13) did not come out with piston block remove
them along with spider (14) and spider pivot (15).
6
The disassembly of the piston block assembly (12) is not
required unless the pins (18) or spring (20) are possibly
damaged.
Caution
The following procedure should be used if the spring is to be
removed from the piston block. The spring (20) is highly
compressed and the retaining ring (21) should not be removed
without compressing the spring (20).
The following parts will be needed to disassemble the piston
block:
2 ea.
3/8 in. I.D. x 1-1/8 in. O.D. flat washers
1 ea.
3/8 in. x 3-1/4 in. N.C. cap screw, and
1 ea.
3/8 in. N.C. nut
Place one of the flat washers over the 3/8 in. x 3-1/4 in. cap
screw and place this through the center of the piston block.
Place the other washer over the cap screw and let it rest on the
three pins. Screw the nut on and compress the spring inside the
piston block. Use a pair of retaining ring pliers and remove the
internal retaining ring (21). Remove the nut, bolt, and the two
washers. Remove the washer (19), spring (20), washer (19),
and three pins (18), and the pin keeper (16).
7
Remove the camplate insert (11) from housing (9). Caution
not to mar the finish that makes contact with pistons.
8
Remove retaining ring (1) from housing. Press shaft (8)
from housing (9) and remove shaft seal (2), and washer (3).
9
Remove retaining ring (4) from shaft and remove thrust
washers (5) and thrust bearing (6).
10 On through shaft assembly, remove snap ring (30) and
shaft seal (29) from backplate.
11 Discard the shaft seals, and o-ring and replace with new
items upon reassembly.
Inspection
1
Check the condition of the needle bearing (25) in backplate
(24) and replace if necessary.
2
Inspect valve plate (22) on the bronze side next to the
piston block for wear. A smooth surface is required. Do not lap
valve plate bronze surface. Replace valve plate if any wear
exists.
3
Inspect the piston block (17) surface that makes contact
with valve plate. This surface should be smooth and free of
deep scratches. Do not lap piston block.
4
The pistons (13) should move freely in the piston block
bore. If they are sticky in the bore, examine the bore for scoring
or contamination.
5
Examine the O.D. of the pistons for finish condition. They
should not show wear or deep scratches. Inspect the shoes for a
snug fit on the ball end of the pistons and a flat smooth surface
that comes in contact with the camplate. Do not lap piston
shoes.
6
Examine the spider (14) for wear in the pivot area.
7
Examine the pivot (15) to insure smoothness and no signs
of wear.
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