Abstract: A combination harvester of conventional type includes a reciprocating sieve onto which the grain and chaff is deposited for separation by differential response to air flow passing through openings in the sieve. The openings in the sieve can be adjusted by an adjustment mechanism in the form of levers positioned at the rear of the sieve. A kit of parts is provided to communicate rotation of the hand crank within the cab of the combine through a flexible pipe which passes through an opening in the combine wall to a screw and nut arrangement which acts to adjust the levers of the sieve adjustment mechanism in dependence upon rotation of the hand crank. The reciprocation of the sieve relative to the combine wall is taken up by flexing of the pipe. The ability to adjust the sieve from within the cab allows on the go adjustment for fine tuning of the separation by the sieve according to harvesting conditions.