Kubota U20-3 Instruction manual

WORKSHOP MANUAL
KUBOTA EXCAVATOR
U20-3
Code No.97899-60740
U25-3

ss
IGeneral
II Machine body
•Mechanism Section......................................................................... II-M-1
•Service Section ................................................................................ II-S-1
III Engine
•05-M Series Engine............................................................................ III-1
•Mechanism Section........................................................................ III-M-1
•Service Section ...............................................................................III-S-1
IV Hydraulic System
•Mechanism Section........................................................................ IV-M-1
•Service Section ...............................................................................IV-S-1
VElectrical System
•Mechanism Section......................................................................... V-M-1
•Service Section ................................................................................ V-S-1
CONTENTS

U20-3, U25-3 WSM General
I-1
I. General
A. Body and engine identification marks.............................................................................................. I-2
B. Safety precautions for servicing, disassembly and reassembly.................................................. I-3
a. Safety measures before starting work .............................................................................. I-3
b. Safety measures during work ........................................................................................... I-3
c. Preparation for disassembly ............................................................................................. I-4
d. Precautions for disassembly and reassembly................................................................... I-4
C. IMPORTANT SAFETY PROCESS AND CRITICAL FUNCTIONAL PROCESS ....................I-5
a. Essential Adhesives.......................................................................................................... I-5
b. Important Safety Process ............................................................................................ I-5
c. Important Critical Functional Process .......................................................................... I-5
D. IMPORTANT INSPECTION ITEMS AFTER REASSEMBLING.................................................. I-5
E. SERVICING FUNDAMENTALS .............................................................................................I-6
a. Items for Servicing ............................................................................................................ I-6
b. O-ring, Oil seal, Circlip and Roll Pin.................................................................................. I-8
c. Piping .............................................................................................................................. I-10
d. Machine Quality Specifications ................................................................................................. I-15
F. Maintenance intervals .......................................................................................................... I-23
a. Maintenance intervals chart ............................................................................................ I-23
b. Hydraulic Oil Check for machines with Hydraulic Breakers ............................................ I-24
c. Periodic replacement of important parts ......................................................................... I-25
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A

U20-3, U25-3 WSM General
I-2
A.Body and engine identification marks
If trouble should occur during use, or if servicing is
necessary, contact the dealer who handles the
machine. At that time please inform the machine
model and engine type and serial numbers.
(1)Machine serial number
(2)Engine serial number

U20-3, U25-3 WSM General
I-3
B.Safety precautions for servicing, disassembly and
reassembly
Safety precautions for servicing
Most accidents during servicing arise from carelessness. Please remember that Safety involves both the
welfare of the employees and improved work efficiency.
Safety precautions for Disassembly and reassembly
Machines must be disassembled and assembled efficiently and safely.
It is very important to thoroughly understand the construction and function of the machine, to make all
appropriate preparations, and start operations according to the specified working procedures.
a. Safety measures before starting
work
(1) Work clothes
1. Wear specified work cap and clothed.
(Under no circumstances may workers
wear undershirts only.)
Cuffs must be kept buttoned, and any tears
must be mended.)
2. Wear safety shoes.
3. Do not wear cotton gloves when working
on the internal section of engine, reduction
gears or hydrauric units for repair or others,
or when using a hammer. Wear leather
gloves, however, when hoisting wires.
(2) Inspecting equipment and tools
1. Prepare equipment (cranes, fork lifts, tool,
etc.) required for servicing and inspect for
any problems before starting work.
2. Hammer heads (metal parts) must be firmly
secured to their handles.
3. Check hosting tools (wire ropes, hoisting
chains, etc.) before use.
(3) Keep workshop in order
1. Secure appropriate space needed for
disassembly to the job.
2. Secure a clean, safe place for arranging
disassembled parts.
3. Store volatile substances (gasoline, light
oil, thinner, oily articles, etc.) in appropriate
containers at selected locations to prevent
fire hazards.
b. Safety measures during work
(1) Protectors
1. Wear goggles when using chisels for
chipping.
2. Use appropriate protectors during welding.
3. Wear a helmet when working with a crane
or at elevated locations.
(2) Team work
1. When working with two or more people,
divide the work and maintain close
communication.
2. Crane work must be carried out using
predetermined signals.
(3) Disassembly and assembly
1. Do not wear gloves when using hammers.
2. Use rods of the specified soft material for
removing pins. Do not use a hammer as a
pad.
3. Do not place fingers in holes when
centering.
4. Heavy parts must be adequately supported
before removing bolts.
(4) Cranes
1. In principle, use a crane for objects heavier
than 44lb (20kg).
2. Crane operation and hoisting must be
performed only by qualified personal.
3. Pay careful attention to the center of
gravity when hoisting, and do not stand
under the lifted objects.
(5) Others
1. To work under a jacked-up carrier, be sure
to place wood pieces under it.
2. When charging batteries, make sure there
are no open flames in the immediate
vicinity.
3. All electric tools must be grounded.
4. Before welding the machine, remove the
battery.
• When removing the battery, be sure to
disconnect negative (-) cord first.
• When mounting the battery, be sure to
connect the positive (+) cord first.

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I-4
c. Preparation for disassembly
(1) Cleaning
Remove mud and dirt from the body before disassembly.
(2) Acceptance inspection
The machine must be checked before it is disassembled to record existing conditions, such as those
listed below.
Model, serial number, and hourmeter reading
• Reason for repair and repair history
• Element stains
• Fuel and oil condition
• Parts damage *(Take photographs if necessary.)
(3) Equipment and tools
prepare equipment, tools, cranes and parts storage racks as required.
d. Precautions for disassembly and reassembly
(1) Disassembly
1. Follow the specified disassembly procedures.
2. Make alignment marks to insure correct reassembly.
3. Arrange disassembled parts in an orderly way, and attach identification tags or put marks if
needed.
(2) Reassembly
1. Clean all parts before assembly. Repair any scratches or dents. Take special precautions against
dirt and dust.
2. Parts with rust-preventive coatings must be assembles only after removing the coating.
3. Separated parts must be correctly reassembled using alignment marks.
4. As a rule, use a press to reassembled bearings, bushing and oil seals. Use pads when using a
hammer.

U20-3, U25-3 WSM General
I-5
C.IMPORTANT SAFETY PROCESS AND CRITICAL
FUNCTIONAL PROCESS
The following instructions are related to essential adhesives, important safety process and critical
functional process .Pay special attention in servicing these process. (Pay also close attention in
reconnecting the electrical cables.)
a. Essential Adhesives
Type of screw adhesive
• Unless otherwise specified, use Three-Bond 1324 adhesive (medium-duty type).
Keep the screw threads free of oil and water.
Type of instantaneous adhesive
• Use Three-Bond 1733 or Three-Bond 1741E adhesive.
Keep the bond areas free of oil and water.
b. Important Safety Process .
1. Reconnecting the fuel hose (clearance, hose routes, clamps, etc.)
2. Electrical cabling (engine, instrument panel, seat stand, etc.) (wiring routes, clamps and couplers)
c. Important Critical Functional Process .
1. Setting up the travel wheel motor (tightening torque)
2. Reassembling the rotary joints (joint direction and shaft set-up)
3. Installing the swivel base bearing and the swivel motor (tightening torque)
4. Fitting the pump couplings (tightening torque)
D.IMPORTANT INSPECTION ITEMS AFTER
REASSEMBLING
a Operate the Machine and check for Unusual Noise and Vibrations.
b Make Sure the Safety decals and Wireharness Clamps are in their Specified
Positions.
c With the Machine Front in a Specified Posture, Check the Amount of Hydrauric
Oil
Checking the oil level (For further details, refer to the Operator’s Manual of each model.)
(1) Park the machine on a level ground.
(2) Make sure the hydrauric oil temperature is in the range of 10-30°C (50-86°F) and see if the oil
level is within the specified zone of the oil level gauge.
(3) Keep the machine front as shown as following posture.
Posture: Extend the rods of the arm and bucket cylinders nearly
half. Place the bucket on the ground, the offset swing at
the center, and the dozer also on the ground.
S
A
S
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I-6
E.SERVICING FUNDAMENTALS
a. Items for Servicing
(1) Tighten bolts, nuts, adapters,and similar parts
to their specified torques which are given in the
list of tightening torques and adhesive as well
as in this manual. Be sure to observe the
specified torques for important tightened parts
and components.
(2) Wipe out water, oil and grease off the screws
on which LOCTITE adhesive is to be applied.
Be sure to apply the adhesive to specified
locations.
The word “LOCTITE“ in this manual denotes the
red-color type.
(3) Precautions in disassembling the hydraulic
equipment
• Use a vacuum pump, plugs, oil pans, waste
cloth and the like to prevent oil from
running out or splashing.
Wipe out leaking oil completely first and
then add oil as required.
• Protect the openings with plugs, covers or
the like to keep off foreign matters. Most of
hydraulic system troubles are caused by
the entry of foreign matters.
• Before reassembling, clean up the parts
and components and apply hydraulic oil on
them.
• The system consists of precision parts. Be
careful not to scratch them and apply
excessive force on them.
Locking adhesive
Types of screw adhesive
Equivalent to LOCTITE 271 (Heavy-duty)
Equivalent to THREE-BOND 1305P (Heavy-duty)
Equivalent to THREE-BOND TB1401B (Light-duty)
Unless specified otherwise, use THREE-BOND 1324
(Medium-duty).
Type of instantaneous adhesive
Use THREE-BOND 1733 or 1741E

U20-3, U25-3 WSM General
I-7
(4) Precautions in tightening hoses and pipes.
• Flexible hoses have a slight natural bend of
their own. Utilize the natural bend. Be also
careful not to twist them.
• Be careful not to confuse the routes of the
hoses.
• Do not hold the hoses in tight contact with
their adjacent parts and surfaces.
• Tightening steps
1. First tighten the nut to its specified
torque.
2. Then loosen the nut by about 45° to fit
the seat of the joint to the connection.
(5) The quantities of oil, fuel, water and others,
except for the oil to be filled in the track rollers
and idlers, are listed just as reference. Fill up
the fluid up to the specified center level of a
level gauge if it is provided.
(6) Security support the machine with a jack and a
supporting jig when it is jacked up for
servicing.
(7) Be sure to use a crane in disassembling and
reassembling heavy parts and components
(frame, front attachment, crawler, etc.).

U20-3, U25-3 WSM General
I-8
b. O-ring, Oil seal, Circlip and Roll
Pin
(1) General precautions
• Make sure the O-ring and the oil seal are
free of anything unusual (uneven surface,
scratches, chipping, etc.).
• Check the O-ring groove for burrs. Correct,
if any, using an oil stone or the like.
• When putting a part past a sharp edge into
position, protect such edge with a cover or
get the part chamfered.
(2) O-ring
• Clean up the O-ring groove and deburr its
edge as required.
• Before installing the ring, be sure to apply
lubricant (grease) over it. (Do not do this to
the floating seal.)
• Fit the O-ring into its groove without twist.
With your fingertip, push the ring gently and
evenly into the final position. Otherwise the
ring would easily get twisted in contact with
the inner edge of the groove.
(3) Floating seal
• Be sure to wipe oil off the O-ring and the O-
ring contact surface. (Note, however, that
oil must be applied thinly over those of the
wheel motor.)
• In fitting the O-ring into the floating seal, be
careful not to twist the O-ring.
• Before installing the floating seal together
with the O-ring, apply sealing oil thinly over
the sliding surface. Be careful to keep the
sliding surface and O-ring in alignment with
the housing.
• Finally turn the floating seal 2 or 3 times by
hand in order to form an oil film over the
sliding surface as well as to get the sealing
surface well it.

U20-3, U25-3 WSM General
I-9
(4) Oil seal
• Do not confuse the orientation of the oil
seal lips. Direct the main lip toward the oil
chamber; in other word, toward what is to
be sealed.
• If in dry state, the oil seal may wear out
when running in the machine. To prevent
this, be sure to apply lubricant (grease)
over the lip sliding surface. If provided also
with a dustproof lip, fill the space between
this lip and the main lip with grease.
• As a rule, use a press to press-fit the oil
seal. If not available, apply a suitable tool
and tap it evenly without allowing any tilt.
Press-fit the oil seal deep down to the
bottom of the oil seal fitting boss.
(5) Mounting the circlip
• Place the circlip with its sharp edge facing
outward (in the locking direction).
• Fit the circlip securely in the groove. For
the hole circlip in particular, install and turn
it slightly to make sure it fits well.
(6) Tapping the roll pin (spring pin)
• Place the roll pin (spring pin) with its
opening perpendicular to the load.
• Place the roll pin (spring pin) with its
opening in the turning direction.
• Evenly tap the roll pin (spring pin) into
position.
a. Packing f. Dustpans lip
b. Metal ring g. Atmosphere (outside)
c. Spring h. Grease
d. Main lip
e. Oil chamber (inside)

U20-3, U25-3 WSM General
I-10
c. Piping
(1) General precautions
• Tightening the pipe socket to the specified torque. If too tight, the socket itself or a hydraulic
component may get damaged. It too loose, an oil leak may result.
• In connecting a new hose or pipe, tighten its nut first to the specified torque and then turn it back
(about 45°). Then tighten it again to the specified torque. (Do not this to the sealing tape-applied
hose or pipe.)
• When disconnecting a vertical hose or pipe, separate its bottom connection first.
• In disconnecting and reconnecting the hose and pipe, be sure to use two wrenches. With one
wrench, restrain the mating part to allow no twist.
• Check the mating connector’s sleeve and the hose’s taper for dust deposits and scratches.
• When the pipe socket has been tightened up, wipe the joint clean. Apply the maximum operating
pressure 2 or 3 times to make sure there is no oil leak.
(2) Hydraulic hose
Check the hydraulic hose for too tight a connect or twist.
*Excessively tight contact
Let’s suppose that a hose is in contact with another hose or other part. If the hose is pulled away by a
force of 2 kg but still in contact, it means the contact is too tight.
(3) Precautions in tightening the bolts and nuts
• Use bolts of specified length.
• Do not over tighten the bolts: Its threads may get deformed or the fixed part may get damaged. Do
not undertighten the bolt either: It may get loose.
• In other words, tighten the bolt to the specified torque.
• Tighten the bolts and nuts diagonally for even tightness.
R (Tapered thread)
G (Straight thread)
Nut
Sleeve
Steel pipe Union nut Tapered thread
Joint body

U20-3, U25-3 WSM General
I-11
(4) Hose screw
(5) Joint bodies
Thread size
(piping screw)
Tightening torque
N·m
kgf·m Wrench size
Union nut section Taper thread section
1/8” 7.8 ~ 11.8 N·m
0.8 ~ 1.2 kgf·m
14.71 ~ 19.61 N·m
1.5 ~ 20 kgf·m17 mm
1/4” 24.5 ~ 29.4
2.5 ~ 3.0
36.3 ~ 44.1
3.7 ~ 4.5 19 mm
3/8” 49.0 ~ 53.9
5.0 ~ 5.5
49.0 ~ 68.6
5.0 ~ 7.0 22 mm
1/2” 58.8 ~ 63.7
6.0 ~ 6.5
83.4 ~ 88.3
8.5 ~ 9.0 27 mm
3/4” 117.7 ~ 127.5
12.0 ~ 13.0
127.5 ~ 147.1
13.0 ~ 15.0 36 mm
1” 137.3 ~ 147.1
14.0 ~ 15.0
147.1 ~ 166.7
15.0 ~ 17.0 41 mm
Thread size
(piping screw)
Tightening torque
N·m
kgf·m Spanner size
(reference)
Remarks
Steel pipe (OD)
R (tapered thread) G (straight thread)
1/8” 19.6 ~ 29.4 N·m
2.0 ~ 3.0 kgf·m—17mm
When in steel
pipe is in use.
8 mm
1/4” 36.3 ~ 44.1
3.7 ~ 4.5
W/O-ring
Joint Torque
58.8 ~ 78.5
6 ~ 8
19 mm 12 mm
3/8” 39.2 ~ 49.0
4.0 ~ 5.0
W/O-ring
Joint Torque
78.5 ~ 98.1
8 ~ 10
23 mm 15 mm
1/2” 49.0 ~ 68.6
5.0 ~ 7.0
W/O-ring
Joint Torque
117.7 ~ 137.3
12 ~ 14
26 mm 16 mm
Metric Size Hose
Thread size
(piping screw)
To r q u e
N·m
kgf·m
M12 ×1.5 20 ~ 30
2.0 ~ 3.1
M14 ×1.5 20 ~ 30
2.0 ~ 3.1
M16 ×1.5 30 ~ 50
3.1 ~ 5.1
M18 ×1.5 30 ~ 50
3.1 ~ 5.1
M22 ×1.5 40 ~ 60
4.1 ~ 6.1

U20-3, U25-3 WSM General
I-12
(6) Tightening torque table for hose clamp (Screw type)
(7) Nuts for piping
No. Dia. (mm) Code No.
Tightening torque
N·m
kgf·m
1 Ø12 ~ 16 09318-89016
2.5 ~ 3.4
25 ~ 35
2 Ø19 ~ 25 09318-89024
3 Ø31 ~ 40 09318-89039
4 Ø36 ~ 46 09318-89045
5 Ø15 ~ 25 RC101-64580 4.9 ~ 5.9
50 ~ 60
6 Ø26 ~ 38 68311-72820
7 Ø13 ~ 20 RB101-63630 3.4 ~ 4.4
35 ~ 45
8 Ø40 ~ 55 RC411-63180
4.9 ~ 5.9
50 ~ 60
9 Ø77 ~ 95 69284-63170
10 Ø50 ~ 60 RC401-63190
11 Ø32 ~ 44 RD411-63820
Steel pipe size
(O.D. × I.D. ×
Thickness)
Tightening torque
N·m
kgf·m
Spanner size
(reference) Remarks
8 × 6 × 1 mm 29.4 ~ 39.2
3.0 ~ 4.0 17 mm
When sleeve nut is in
use.
10 × 7 × 1.5 mm 39.2 ~ 44.1
4.0 ~ 4.5 19 mm
12 × 9 × 1.5 mm 53.9 ~ 63.7
5.5 ~ 6.5 21 mm
16 × 12 × 2 mm 88.3 ~ 98.1
9.0 ~ 10.0 29 mm
18 × 14 × 2 mm 127.5 ~ 137.3
13.0 ~ 14.0 32 mm
27.2 × 21.6 × 2.8 mm 235.4 ~ 254.97
24.0 ~ 16.0 41 mm

U20-3, U25-3 WSM General
I-13
(8) Tightening torque of bolts and nuts
Refer to the tightness torque table below.
(9) Types and materials of bolts and nuts
[ex. bolts]
Bolts, Nuts
Nominal Dia.
4T 7T 9T
SS41 S40C, S45C SCr4
M6 7.8 ~ 9.3 N·m
0.80 ~ 0.95 kgf·m
9.8 ~ 11.3 N·m
1.00 ~ 1.15 kgf·m
12.3 ~ 14.2 N·m
1.25 ~ 1.45 kgf·m
M8 17.7 ~ 20.6 N·m
1.80 ~ 2.10 kgf·m
23.5 ~ 27.5 N·m
2.40 ~ 2.80 kgf·m
29.4 ~ 34.3 N·m
3.00 ~ 3.50 kgf·m
M10 39.2 ~ 45.1 N·m
4.00 ~ 4.60 kgf·m
48.0 ~ 55.9 N·m
4.90 ~ 5.70 kgf·m
60.8 ~ 70.6 N·m
6.20 ~ 7.20 kgf·m
M12 62.8 ~ 72.6 N·m
6.40 ~ 7.40 kgf·m
77.5 ~ 90.2 N·m
7.90 ~ 9.20 kgf·m
103.0 ~ 117.7 N·m
10.50 ~ 12.00 kgf·m
M14 107.9 ~ 125.5 N·m
11.00 ~ 12.80 kgf·m
123.6 ~ 147.1 N·m
12.60 ~ 15.0 kgf·m
166.7 ~ 196.1 N·m
17.00 ~ 20.00 kgf·m
M16 166.7 ~ 191.2 N·m
17.00 ~ 19.50 kgf·m
196.1 ~ 225.6 N·m
20.00 ~ 23.00 kgf·m
259.9 ~ 304.0 N·m
26.50 ~ 31.00 kgf·m
M18 245.2 ~ 284.4 N·m
25.00 ~ 29.0 kgf·m
274.6 ~ 318.7 N·m
28.00 ~ 32.50 kgf·m
343.2~ 402.1 N·m
35.00 ~ 41.00 kgf·m
M20 333.4~ 392.2 N·m
34.00 ~ 40.00 kgf·m
367.7 ~ 431.5 N·m
37.50 ~ 44.0 kgf·m
519.8 ~ 568.8 N·m
53.00 ~ 58.00 kgf·m
Types Material Tensile strength Hardness Bolt head marking
4T SS41 Over 392 MPa
4000 kgf/cm2
HRB
62 ~ 98 No mark or marked 4
7T S40C
S45C
Over 686 MPa
7000 kgf/cm2
HRC
20 ~ 28 Marked 7
9T SCr4 Over 882 MPa
9000 kgf/cm2
HRC
28 ~ 34 Marked 9

U20-3, U25-3 WSM General
I-14
(10)Washer-equipped elbow
Tightening torque
Tightening procedure
1. Connecting with the valve
• Screw in the elbow by hand until the
washer comes into contact.
Note: Clean up the mating seal beforehand.
2. Positioning
• Turn the elbow back to its set position.
Note: Do not make any more than one turn back.
3. Fixing
• Tighten up the lock nut with a wrench.
• Lock nut tightening torque
Size N·m kgf·m
G1/4 25 ~ 30 2.5 ~ 3.0
G3/8 49 ~ 54 5.0 ~ 5.5
G1/2 59 ~ 64 6.0 ~ 6.5
G1/8 15 ~ 16.5 1.5 ~ 1.7

U20-3, U25-3 WSM General
I-15
d. Machine Quality Specifications
Machine specification:Service port, Wrist rest, STD-arm, KBT-cab, KBT-bucket
No Specifications Items Unit U20-3 U25-3 Remarks
Q1 Main Spec. JIS A8404
1
1
Machine size
Total length
(Transport) mm 3848 ± 77 4107 ± 82
2 Total width mm 1400 ± 14 1500 ± 15
3 Total height (Canopy) mm 2375 ± 24 2420 ± 24
4 Total height (Cabin) mm 2355 ± 24 2400 ± 24
2
1
Weight
Machine weight
(Canopy) kg 2030 ± 102 2460 ± 123 Fuel tank
2Machine weight
(Cabin) kg 2120 ± 106 2540 ± 127
3
1
Performance
Swivel speed
L rpm 8.9 ± 0.9 9.5 ± 0.9
2 R rpm 8.9 ± 0.9 9.5 ± 0.9
3
Travel speed
Rubber F1 km/h 2.2 ± 0.2 2.5 ± 0.2
4 Rubber F2 km/h 4.2 ± 0.4 4.5 ± 0.4
5 Iron F1 km/h 2.1 ± 0.2 2.4 ± 0.2
6 Iron F2 km/h 4.0 ± 0.4 4.4 ± 0.4
7 Gradeability deg 30< 30<
4
1Rear end min. turning
radius mm 720 ± 14 765 ± 15
2Swivel frame rear
ground clearance mm 490 ± 10 524 ± 10
3Tambler center
distance mm 1474 ± 44 1561 ± 47
4 Crawler total length mm 1851 ± 56 1996 ± 60
5 Crawler total width mm 1400 ± 30 1500 ± 30
6 Min. ground clearance mm 265 ± 8 300 ± 9
5
1
Front attachment
Bucket heaped
capacity
Heaped m30.066 ± 0.003 0.08 ± 0.003
SAE, JIS
2Struck
m30.045 ± 0.002 0.053 ± 0.002
3 Bucket width mm 450 ± 10 500 ± 10 Without side cutter
4
Swing angle
Canopy L deg 73 ± 2 73 ± 2
5 Canopy R deg 55 ± 2 55 ± 2
6 Cabin L deg 73 ± 2
7 Cabin R deg 55 ± 2