Hitachi DH 40FR Technical Data And Service Manual page 16

Sealing and dust-proof structure
The cylinder crank case section is tightly sealed with three o-rings, two oil seals and rubber seal as shown in
Fig. 7. This prevents leakage of grease from the cases, while also protecting them against dust from outside.
For additional dust-proof protections, a standard accessory dust cover is provided which serves to prevent
dust and chips from entering the spline hole of the second hammer and causing imperfect fitting of the drill bit.
Rubber seal
O-ring
Oil seal
O-ring O-ring
Oil seal
Dust cover
Fig. 7
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