A combine harvester having a sieve that is moveable by a sieve drive assembly to perform a reciprocating sieve movement having a sieving stroke and a sieve throwing angle, wherein the sieve drive assembly has: a rotary drive, having a rotatable output shaft, a transmission between the rotatable output shaft of the rotary drive and the sieve, which transmission comprises an eccentric device, at least one transmission element, a plurality of linkage pivots, a first non-adjustable transmission element which is pivotably connected to the eccentric device, wherein the first non-adjustable transmission element is further pivotably connected to the adjustable transmission element, which adjustable transmission element is further pivotably connected to the combine harvester chassis, and wherein the first non-adjustable transmission element is further pivotably connected to the sieve through at least one further non-adjustable transmission elements.