An agricultural harvesting machine for crop material may include a pre-compression chamber having an accumulation phase in which crop material accumulates until a pre-determined fill condition and a loading phase in which crop material transfers from the pre-compression chamber into a compression chamber when the pre-determined fill condition has been attained. The agricultural harvesting machine may include a crank arm connected to a rotational power source. The agricultural harvesting machine may include a plunger having an extended position which is located further rearward in a compression chamber than a retracted position. The movement of the plunger can be decoupled from the movement of the crank arm during the accumulation phase and can be moved to the extended position following the loading phase. The agricultural harvesting machine may also include a connecting link connected between the plunger and a rotational power source, with one of the connecting link and the crank arm having a variable length.
