A mobile lift crane includes a carbody having moveable ground engaging
members; a rotating bed rotatably connected to the carbody such that the
rotating bed can swing with respect to the ground engaging members; a
boom pivotally mounted on a front portion of the rotating bed; a mast
mounted at its first end on the rotating bed; a backhitch connected
between the mast and a rear portion of the rotating bed; a moveable
counterweight unit; at least one hydraulic cylinder; and at least one arm
pivotally connected at a first end to the rotating bed and at a second
end to the hydraulic cylinder. The arm and hydraulic cylinder are
connected between the rotating bed and the counterweight unit such that
extension and retraction of the hydraulic cylinder changes the position
of the counterweight unit compared to the rotating bed. In one method of
operation, the counterweight is positioned forward of a point directly
below the top of the mast when no load is on a load hoist line suspended
from the boom; and positioned reward of the top of the mast when the
hoist line supports a load; and the moveable counterweight is never
supported by the ground during crane pick, move and set operations other
than indirectly by the ground engaging members on the carbody. In another
method the crane is used to perform a pick, move and set operation with a
load wherein the move able counterweight is moved toward and away from
the front portion of the rotating bed by extending and retracting the
hydraulic cylinder during the pick, move and set operation to help
counterbalance the load, but the counterweight is never supported by the
ground other than indirectly by the ground engaging members on the
carbody.