a bail assembly including bail members moveable between operative engaged positions and a disengaged position ; bail actuating structure for quickly moving the bail members between the operative engaged positions and the disengaged position , and holding devices for holding the bail members at any selected operative engaged position . preferably the holding device is a selectively releasable self locking hydraulic cylinder assembly which includes adjustable holding device , a locking chamber associated with the adjustable holding device which may be filled to lock the adjustable holding device , control structure for controlling flow of fluid to and from the locking chamber , and actuating structure for selectively actuating the control structure .