Hitachi H 45MRY Technical Data And Service Manual page 24

Mounting the piston
Insert the Piston Pin [34] into the 8-mm dia. hole (marked) of the Piston [35] and the Connecting Rod [36]
then press-fit it. Mount the O-ring (I.D 27.2) [33] to the Piston [35]. At this time, do not protrude the Piston Pin
[34] from the outside of the Piston [35]. Move the crank pin of the Crank Shaft [42] to the bottom dead center
and insert the piston ass'y into the Crank Shaft [42] from the cylinder case of the Cylinder Crank Case [47].
Mount the Retaining Ring for D10 Shaft [37] using a retaining ring puller (Fig. 20).
Piston pin
D8 hole
O-ring
Piston
Mounting the cylinder
Insert the concave side of the Slide Sleeve [31] into the Cylinder [30]. Insert the assembly of the Striker [28]
and the O-ring (I.D 27.2) [29] into the Cylinder [30] (Fig. 21).
Connecting rod
Mark
Cylinder crank case
Concave
Slide sleeve
Striker
Retaining ring
Fig. 20
Cylinder
O-ring
Fig. 21
--- 21 ---
Crank pin portion
Crank shaft