An agricultural harvesting machine for crop material including 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 crank arm and the plunger. The movement plunger is decoupled from the movement of the crank arm during a startup mode of the agricultural harvesting machine. The movement plunger is coupled to the movement of the crank arm during a run mode of the agricultural harvesting machine. The connecting link, crank arm, or both have a variable length.
