Hitachi NR 90AD Technical Data And Service Manual page 25

(a) Reassembly
Disassembly procedures should be followed in the reverse order. Note the following points.
Charge the sliding portion of the Head Valve [9] of the Exhaust Cover [5] with about 3 grams of grease and
apply grease to each surface of the O-rings.
As shown in Fig. 12, firmly push the Exhaust Valve Rubber [11] until it is fully seated over the projection of the
Exhaust Cover [5].
Mount the Sheet [3] in the direction as shown in Fig. 13 aligning the center of the hole of the Sheet [3] with the
center of the bolt hole of the Exhaust Cover [5]. If not aligned, abnormal exhaust noise may be heard.
Sheet [3]
Head Valve [9]
Push until the rubber is fully
seated over the projection.
Exhaust Valve Rubber [11]
Exhaust Cover [5]
Apply grease of 3 grams
to the sliding potion.
Fig. 12
Exhaust Cover [5]
Fig. 13
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Align the center of the hole of
the Sheet [3] with the center
of the bolt hole of the Exhaust
Cover [5].