Hitachi DH 24DVA Technical Data And Service Manual page 37

(6) Mounting the Piston [39]
Mount the Piston [39] facing its two 2-mm diameter holes to Second Shaft (A) [49] as shown in Fig. 25.
(7) Mounting Gear Cover (A) [10]
First, mount Change Lever (A) [19] and the lock plate ass'y to Gear Cover (A) [10] then mount it to the main
body as shown in Fig. 25. At this time, engage the gear in 3 points (A, B and C) as shown in Fig. 26 according
to either of the following methods:
Mount the drill bit and turn it by a hand slowly, or
1
2 Install the battery and pull the trigger switch for a quick moment to turn the motor.
Inner Cover Ass'y [42]
Striker [37]
Second Shaft (A) [49]
Reciprocating Bearing [51]
First Gear [53]
Fig. 25
C point
Fig. 26
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Piston [39]
A point
B point