Komatsu PC138US-11 Operation & Maintenance Manual page 249

OPERATION MACHINE OPERATIONS AND CONTROLS
PROHIBITION OF OPERATIONS USING BUCKET AS LEVER
Do not put the bucket back to a rock and use it as a lever to
dig. This can apply an excessive force to the chassis and buck-
et, and the machine may break.
In this case, dig by using only the force of the arm or bucket. If
an excessive force is applied, the safety valve of the hydraulic
system controls it into a proper range to prevent breakage of
the machine.
PROHIBITION OF OPERATIONS USING MACHINE DROPPING FORCE
Do not use the dropping force of the machine for digging.
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