The arcuate processing assembly of a combine harvester may be pivotally adjusted generally radially toward or away from a rotary processing device to adjust the operating clearance between the periphery of the rotary device and the assembly. Simultaneously with such adjustment of the assembly as a whole, in a compound pivoting action one arcuate member of the assembly is also pivoted relative to the other arcuate member to properly reshape the threshing region for the adjusted running clearance. Alternative embodiments are disclosed for axial flow and transverse flow systems.