In a crop threshing mechanism comprising a threshing cylinder (3) located adjacent a concave threshing grate (6) and driven to thres crop fed tangentially between the first rotor and grating, a crop conveyor (27), in the form of a roller or continuous band conveyor, is located along the leading edge of the grate (6), with respect to the crop feed direction so that crop passes over it to the first rotor (3) and grating (6), and a changeable speed drive mechanism drives the conveyor (27) and allows its speed to be changed, thereby to control the speed of crop flow. A crop elevator (5) is supported to pivot about the axis of the first rotor (3) to raise and lower a crop collecting table (4) carried at the bottom of the elevator, the conveyor (27) being located between the upper end of the elevator floor (25) and the leading edge of the grate (6) so as to form a substantially continuous crop flow path with said floor and grate. The grate (6) and conveyor (27) are mounted so as to pivot with the elevator (5) about the axis of the first rotor (3). A crop guide flap (34) is provided adjacent the conveyor (27) to vary the angle at which the crop is fed to the first rotor (3).