An attachment for increasing the lifting capacity of a crane having a mobile lower works with an upper works including a rear portion rotatably mounted thereon and having a pivotally mounted boom and an upwardly and rearwardly projecting mast carried on the upper works with means for lifting a load from the top of the boom and rigging means interconnecting the top of the boom, the top of the mast and the rear portion of the upper works, including a counterweight support beam detachably connected to the crane upper works and extending rearwardly therefrom, a counterweight assembly including a movable carrier mounted on the support beam for movement along the length thereof, an actuator for selectively moving the counterweight carrier fore and aft along the beam, a leg for normally supporting the trailing end of the beam on the ground, and a rear pendant interconnecting the trailing end of the beam and the top of the mast for raising the leg from the ground incident to lifting a heavy load from the boom.
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