A harvesting machine may include a main frame, a rotor assembly rotatably coupled to the main frame, a top frame movably attached to the main frame forming a passageway for crop material between the top frame and the rotor assembly, a bottom frame movably attached to the top frame, a plurality of knives movably attached to the top and bottom frames, and an actuator operatively connected to one of the top frame and the bottom frames. The plurality of knives extends through slots in the top frame. The top and bottom frames and the plurality of knives are in a raised position when the actuator is in a first position. The top and bottom frames and the plurality of knives are in a lowered position when the actuator is in a second position, which enlarges the passageway and partially retracts the knives through the slots in the top frame.