A combine harvester (10) includes a frame (12) and two axial-flow crop processing rotors (21,22) mounted to the frame. An inner support structure (32) is located between the two rotors and is mounted to the frame by a first linkage (34). Two outer support structures (42,52) are located outboard of the two rotors (21,22) and are mounted to the frame (12) by respective second and third linkages (44,54). The inner support structure and two outer support structures carry first and second pluralities of concave grate segments (30,31) at a radial distance (C) from the respective rotors. A concave adjustment system includes a first actuator (81) coupled to the first linkage (34) which is configured to raise and lower the inner support structure (32). A second actuator (82；83) is coupled to one of the second and third linkages (44；54) and is configured to raise and lower at least one of said two outer support structures (42；52).
