Komatsu PC138USLC Operation & Maintenance Manual page 367

RECOMMENDED ATTACHMENT OPERATIONS RECOMMENDED ATTACHMENT OPERATIONS
When applying continuous impact to the same impact surface, if
the chisel does not penetrate or break the surface within 1 minute,
change the point of impact and carry out breaking operations
closer to the edge.
The direction of penetration of the chisel and the direction of the
breaker body will gradually move out of line with each other, always
adjust the bucket cylinder to keep them aligned.
Always keep the chisel pressed against the impact surface
properly to prevent using the impact force when there is no
resistance.
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ATTACHMENTS AND OPTIONS ATTACHMENTS AND OPTIONS