An agricultural harvesting machine for crop material may include a crank arm connected to a rotational power source, a plunger having an extended position which is located further rearward in a compression chamber than a retracted position, and a connecting link connected between the plunger and the crank arm, with one of the connecting link and the crank arm having a variable length. The agricultural harvesting machine may include a startup mode and a run mode. The movement of the plunger can be decoupled from the movement of the crank arm at the beginning of the startup mode. The plunger can move to a predetermined position during the startup mode. The movement of the plunger can be coupled to the movement of the crank arm during the run mode.
