A center knife drive for a sickle of a plant cutting machine having an upwardly facing cover and at least one output element reciprocatingly movable by the drive above the cover for moving a knife of the sickle in a sideward reciprocating cutting action, including at least one cleaning flap in connection with the output element positioned and configured for reciprocating forward and rearward movement thereby, disposed above the cover and configured for cleaning loose material therefrom during the movement and for pushing the loose material from the cover to accommodate upward movement of the drive within a space below or in a floor of the machine, clearing the material from the path of the output element, and improved heat dissipation.