The invention provides a positioning apparatus (17) for a rotary combine harvester (100) having a threshing concave (6a) and a separation grate (6b). The apparatus (17) has a concave adjustor mechanism for adjusting a threshing gap between the threshing concave (6a) and a rotor or rotors (5) of the harvester (100). The concave adjustor mechanism has a concave actuator (33) including a concave hydraulic cylinder having an adjustable hydraulic pressure to cause rotation of a concave control arm (31) so as to control a position of the threshing concave (6a). The apparatus (17) also has a grate adjustor mechanism for adjusting a separation gap between the separation grate (6b) and the rotor or rotors (5) of the harvester (100). The grate actuator mechanism has a grate actuator (330) including a grate hydraulic cylinder having an adjustable hydraulic pressure to cause rotation of the grate control arm (310) so as to control a position of the separation grate (6b). The concave hydraulic cylinder and the grate hydraulic cylinder both extend in a longitudinal direction (X) of the apparatus (17). Advantageously, the threshing and separation gaps may be adjusted independently and relatively quickly. Also advantageously, the invention provides a compact, space-saving layout for the apparatus (17).