A large square baler (10) is equipped with a plunger drive incorporating a flywheel (34) configured as or carrying a fan which creates a flow of air within a housing (58) disposed about the flywheel (34). A duct arrangement (64) is coupled between the housing (58) and a knotter table housing (52) so that air is directed across and maintains a plurality of knotters (50) located in the knotter table housing (52) free of debris.
