Hitachi DH 24PG Assembly instructions

LIST Nos.
DH 24PG: F420
DH 26PB: F417
DH 28PBY: F414
May 2013
PRODUCT NAME
Hitachi Rotary Hammer
Models DH 24PG
DH 26PB
DH 28PBY
D
DH 28PBY
Sales Division
REPAIR GUIDE

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1. Precautions on disassembly and reassembly ----------------------------------------------------------- 1
STANDARD REPAIR TIME (UNIT) SCHEDULES ------------------------------------------------------------------ 19
CONTENTS Page

-1-
Be sure to disconnect the power cord plug from the power supply before conducting repair. Otherwise, the
motor may suddenly turn on, posing a very dangerous situation.
1. Precautions on disassembly and reassembly
(Bold) numbers in the descriptions below correspond to item numbers in the Parts List and exploded
assembly diagram for the Model DH 24PG, <Bold> numbers to those for the Model DH 26PB, and {Bold}
numbers to those for the Model DH 28PBY. [Bold] numbers correspond to item numbers for the Models
DH 24PG, DH 26PB, and DH 28PBY.
1. Disassembling the tool retainer ass’y
Fully pull the Grip [3] in the arrow direction and detach the Front Cap [1].
Then use the retaining ring puller to remove the Stopper Ring [2], while pulling the Grip [3] in the arrow
direction. You can now detach the Grip [3], Ball Holder [4], Steel Ball D7.0 [19], Holder Plate [5], and
Holder Spring [6] from the Cylinder [20].
Disassembly
REPAIR GUIDE
Fig. 1 ƔDisassembling the tool retainer ass’y
Grip [3]
Front Cap [1] Holder Plate [5]
Ball Holder [4]
Stopper Ring [2]
Cylinder [20]
Steel Ball D7.0 [19]
Grip [3]
Holder Spring [6]

-2-
Fig. 2 ƔRemoval of the change lever
Change Lever (13)<12>{12} Pushing Button [11] pin route
2. Removing the change lever
Push in the Pushing Button [11] at the "Rotation + Hammering" ( mark) position, turn the Change
Lever (13)<12>{12} counterclockwise a little, and then fully push in the Pushing Button [11]. In this state,
turn the Change Lever (13)<12>{12} clockwise. When the lever stops, release the Pushing Button [11]
and then turn the Change Lever (13)<12>{12} clockwise. When the lever stops again, push in the Pushing
Button [11] and then turn the Change Lever (13)<12>{12} clockwise once more. At this position, ply up
the Change Lever (13)<12>{12} in order to remove it.

-3-
Fig. 3 ƔDisassembling the hammering mechanism
Hand press
Rear end of the Second Shaft [41]
Clutch [44] end face
Clutch
[
44
]
end face
3. Disassembling the hammering mechanism
Use a drill bit or screwdriver to push in the Second Hammer [30], and then remove the Striker [36] that is
chucked by O-ring (C)[33]. Remove the Tapping Screw (W/Flange) D5 x 35 (66)<66>{76} from the
Housing (65)<65>{75} and then detach the Gear Cover [7]. Do not let the Inner Cover [53] come off from
the Housing (65)<65>{75}. Otherwise, the Armature (59)<59>{65} will come off together with the Inner
Cover [53], thereby damaging its carbon brushes and the commutator.
Remove the Seal Lock Hex. Socket Hd. Bolt M5 x 16 [48] from the Bearing Holder [49], rotate the Second
Shaft [41] to allow the Piston [38] to reach the top dead point (towards the Inner Cover [53]). The
Reciprocating Bearing [47] arm comes off from the Piston Pin [39] and parts on the Second Shaft [41]
come off together from the Inner Cover [53]. The Seal Lock Hex. Socket Hd. Bolt M5 x 16 [48] loses its
bonding force when disassembled. Accordingly, it must be replaced by a new one when reassembled.
Hold the end face of the Clutch [44] as shown below, use a hand press to push the rear end of the
Second Shaft [41] in order to push out the First Gear [51], Bearing Cover [50], Ball Bearing
608VVC2PS2L [17], Bearing Holder [49], Bearing Washer [18], Reciprocating Bearing [47], Clutch [44],
Change Plate [46], Washer [45], Clutch Spring [43], and Washer (C) [42] from the Second Shaft [41].
Note that the First Gear [51] is press-fitted to the rear end of the Second Shaft [41] for alignment.

-4-
4. Disassembling the cylinder ass’y
(1) Disassembly of the slip clutch ass’y
Remove the tool retainer ass’y and pull out the Cylinder [20] ass’y from the Gear Cover [7]. Remove
Washer (A) [25] from the Cylinder [20] and then use the retaining ring puller to pull out the Retaining Ring
for D30 Shaft [26]. Washer (A) [25], Spring (A) [24], the Second Gear [23], Cylinder Clutch [22], and Pin
D2.5 [21] can now be removed from the Cylinder [20].
(2) Disassembly of the cylinder inside
Insert stopper ring jig (A) (J-341) into the Cylinder [20] from the non-hole side as shown in Fig. 4 until it
contacts the end of the Damper Holder [34]. Clamp the ends of the Cylinder [20] and stopper ring jig (A)
(J-341) with a vise to compress Damper (A) [32]. (Push the Stopper Ring [35] with punch (C) (J-341) and
make sure it moves a little.) In this state, insert punch (C) (J-341) into each of the two ĭ8 holes on the
Cylinder [20]. Hammer the punch head to give force to the periphery of the Stopper Ring [35] in order to
detach the ring from the bore groove of the Cylinder [20]. Fully hammer along the periphery of the Stopper
Ring [35] until the Stopper Ring [35] disappears from the two ĭ8 holes.
Then unclamp the Cylinder [20] from the vise and use ring puller jig (B) (J-341) to pull out the Stopper
Ring [35] from the inner circumference of the Cylinder [20]. Be careful not to let the Stopper Ring [35] pop
out. Once the Stopper Ring [35] is detached from the Cylinder [20], Hammer Holder (C) [28], Sleeve (FW)
[29], the Second Hammer [30], Hammer Holder (A) [31], Damper (A) [32], O-ring (C) [33], and the
Damper Holder [34] can be removed from the Cylinder [20]. Here the Stopper Ring [35] is deformed by
disassembly and must be replaced by a new one when reassembled. Replace O-ring (C) [33] with a new
one at each disassembly to prevent dry firing.
Fig. 4 ƔDisassembling the cylinder ass’y
Hammer the punch head.
Punch
(
C
)
(
J-341
)
ĭ8 hole (2 holes)
Vise
Vise
Damper (A) [32]
Sleeve (FW) [29]
Hammer Holder (A) [31]
Hammer Holder (C) [28]
Stopper ring jig (A) (J-341)
Second Hammer [30] O-ring (C) [33]
Damper Holder [34]
Stopper Ring [35]

-5-
Reassembly can generally be conducted by reversing the disassembly procedure. However, special
attention should be given to the following items.
1. Reassembling the cylinder ass’y
Insert the set of Hammer Holder (C) [28], Sleeve (FW) [29], the Second Hammer [30], Hammer Holder
(A) [31], Damper (A) [32], O-ring (C) [33], and the Damper Holder [34] into the Cylinder [20] to which Oil
Seal (A) [27] is press-fitted. (Do not reverse the seal orientation.) (Assemble with the bore slope of
Hammer Holder (C) [28] set at the rear end and with the Sleeve (FW) [29] notch set at the front end as
shown in Fig. 5. Do not reverse the assembly order.) Push a new Stopper Ring [35] into the Cylinder [20]
with the break of the Stopper Ring [35] facing away from the ĭ8 hole on the Cylinder [20] as shown in Fig.
5. With the ring break facing toward the ĭ8 hole, the cylinder assembly is difficult to disassemble. Note the
ĭ8 hole on the Cylinder [20] and correctly orient the Stopper Ring [35] as shown in Fig. 5 when pushing in.
Insert stopper ring jig (A) (J-341) from the hole side and use a hand press to press against the upper end
of the jig until the Stopper Ring [35] is fitted into the bore groove of the Cylinder [20]. Confirm that the
Stopper Ring [35] is fit securely into the bore groove of the Cylinder [20] through the two ĭ8 holes on the
periphery of the Cylinder [20].
Reassembly
Fig. 5 ƔInside structure of the cylinder ass’y
Hand press
Second Hammer [30]
Hammer Holder (C) [28]
Hammer Holder (A) [31]
Damper (A) [32]
Sleeve (FW) [29]
ĭ8 hole (2 holes)
Damper Holder [34]
O-ring (C) [33]
Stopper ring jig (A) (J-341)
Stopper Ring [35]
Oil Seal (A) [27]
Sleeve (FW) [29] notch
Cylinder [20]
ĭ8 hole
ĭ8 hole
Stopper Ring [35] break
Bore slope of Hammer Holder (C) [28]

-6-
2. Press-fitting the first gear
Match the end of the First Gear [51] with the rear end of the Second Shaft [41] and then press-fit. After
press-fitting the First Gear [51], confirm that the inner ring of the Reciprocating Bearing [47] shaft rotates
smoothly.
3. Mounting the oil seals
In reassembly of the Oil Seal [9] and Oil Seal (A) [27], apply grease to the inner circumferences of both
seals, but do not apply grease along their peripheries. Be careful not to skew the Oil Seal [9] and Oil Seal
(A) [27] when press-fitting these parts.
4. Reassembling the internal pressure adjusting mechanism
Insert Felt Packing (A) (64)<64>{71} into the hole on the Air Cap (63)<63>{70} and lay the Air Cap
(63)<63>{70} over the ĭ8.4 shaft of the Inner Cover [53]. Fit the inside boss of the Air Cap (63)<63>{70}
hole to the groove on the ĭ8.4 shaft of the Inner Cover [53].
Fig. 6 ƔReassembling the internal pressure adjusting mechanism
Air Cap (63)<63>{70}
Felt Packing (A) (64)<64>{71}
Fit the boss to the groove.
Inner Cover [53]
A – A (2:1)
A
A

-7-
5. Reassembling the low vibrations mechanism (DH 28PBY)
Degrease Weight Damper (A) <54> bonding area of the Inner Cover <53> and then bond Weight Damper
(A) <54> to the area. Degrease the threaded portion of Weight (A) <55>, mount Weight (B) <57> and the
Leaf Spring <56> on Weight (A) <55>, and then secure both parts with the Seal Lock Hex. Socket Hd. Bolt
M3 x 8 <58>. Degrease the threaded portion of the Inner Cover <53>. Insert the Spring Damper <72> into
the Inner Cover <53> and Spring Holder <73>, and then secure the Leaf Spring <56> and Spring Holder
<73> with the Seal Lock Hex. Socket Hd. Bolt M4 x 12 <74>. Place Weight (A) <55> on the Inner Cover
<53> side and Weight (B) <57> on the Housing <75> side. Do not reverse the positions.
Degrease Weight Damper (B) <66> bonding area of the Fan Guide <67> and bond Weight Damper (B)
<66> to the area. Mount the Cover Plate <64> before inserting the Armature <65> into the Inner Cover
<53>. Mount the Cover Plate <64> with its body projected toward the Inner Cover <53> as shown in Fig. 7.
Fit the projection of the Inner Cover <53> into the hole on the Cover Plate <64>.
Fig. 7 ƔReassembling the low vibrations mechanism
Inner Cover <53>
Weight Damper (A) <54> bonding area
Weight Damper (B) <66> bonding area
Spring Damper <72>
Thread
Weight Damper (B) <66>
Fan Guide <67>
Seal Lock Hex. Socket
Hd. Bolt M4 x 12 <74>
S
p
rin
g
Holder <73>
Cover Plate <64>
Weight (A) <55> Wei
g
ht
(
B
)
<57>
Thread
Leaf Spring <56>
Seal Lock Hex. Socket
Hd. Bolt M3 x 8 <58>

-8-
Fig. 8 ƔMounting the piston
Inner Cover [53] ass’y
Breathing groove of Piston [38]
Piston [38]
Striker [36]
O-ring D17 [37]
Air chamber
6. Mounting the piston
Mount the Piston [38] as shown in Fig. 8.
Apply the specified grease to the inner and outer circumferences of the Piston [38]. Also apply grease to
the inner and outer circumferences of the Piston Pin [39] and Piston Washer [40]. Mount the Piston
Washer [40] on the Piston [38] and then insert the Piston Pin [39].
Fill 20 grams of the specified grease into the cylinder of the Inner Cover [53] and then insert the Piston
[38] into the cylinder of the Inner Cover [53]. Insert the arm of the Reciprocating Bearing [47] of the
Second Shaft [41] assembly into the Piston Pin [39] so that the arm of the Reciprocating Bearing [47] is
sandwiched between the two Piston Washers [40] as shown in Fig. 9.
After inserting the arm, insert the spigot joint of the Bearing Holder [49] into the Inner Cover [53] with the
threaded portions of the Inner Cover [53] aligned with the holes of the Bearing Cover [50] and Bearing
Holder [49]. Here, orient the Bearing Holder [49] as shown in Fig. 10.
As shown in Fig. 11, one of the bolts touches the Reciprocating Bearing [47] and cannot be inserted
straight into the Inner Cover [53]. Therefore, tighten one bolt at a time, rotate the Reciprocating Bearing
[47] so that new Seal Lock Hex. Socket Hd. Bolt M5 x 16 [48] can be inserted straight in, and then fully
tighten the bolts.
After tightening the bolts, allow the Reciprocating Bearing [47] to make one rotation and confirm that the
Piston [38] makes one reciprocation. Pull the Piston [38] to confirm that it does not come off.
Pushing the Striker [36] into the Piston [38] compresses the air in the air chamber. The compressed air is
released when O-ring D17 [37] exceeds the breathing channel of the Piston [38]. Push in the Striker [36]
until O-ring D17 [37] exceeds the breathing channel of the Piston [38]. (Listen for the sound of air being
released when O-ring D17 [37] exceeds the breathing channel of the Piston [38].)

-9-
Fig. 9 ƔMounting the piston Fig. 10 ƔMounting the bearing holder
Fig. 11 ƔTightening the bolts
Piston Washer [40]
Piston [38]
Arm of Reciprocating Bearing [47]
Bearing Cover [50]
Inner Cover [53]
Bearing Holder [49]
Seal Lock Hex. Socket Hd.
Bolt M5 x 16 [48]
CAUTION: Do not tighten the bolt when
it is skewed in contact with
the reciprocating bearing.
Flat portion of Bearing Holder [49]
Inner Cover [53]