Combine harvester comprising a combine harvester chassis and a cleaning shoe for separating threshed grain from material other than grain, said cleaning shoe comprising at least one sieve (5, 6, 10) and an associated sieve drive assembly, said sieve (5, 6, 10) being moveable by said sieve drive assembly to perform a reciprocating sieve movement having a sieving stroke and a sieve throwing angle, wherein the sieve drive assembly comprises: - a rotary drive, which rotary drive comprises a rotatable output shaft, - a transmission that provides a connection between the rotatable output shaft of the rotary drive and the sieve, which transmission is adapted to transform a rotational movement of the rotatable output shaft into the reciprocating sieve movement of the sieve, which transmission comprises an eccentric device, one or more transmission elements (31, 32, 33, 34, 40), and a plurality of linkage pivots (50,51,52,53,54,55), wherein the eccentric device has an input that is connected to the rotatable output shaft and an output that is pivotably connected to one of the one or more transmission elements (31, 32, 33, 34, 40) through one of the plurality of linkage pivots (50,51,52,53,54,55), which eccentric device has an eccentricity for inducing movement of the at least one transmission element, and wherein each transmission element (31, 32, 33, 34, 40) is associated with at least two associated linkage pivots (50,51,52,53,54,55), wherein each associated linkage pivot pivotably connects said transmission element with one of: another transmission element of the one or more transmission elements (31, 32, 33, 34, 40), the eccentric device, the sieve and/or the combine harvester chassis, characterised in that the eccentric device is an adjustable eccentric device in which the eccentricity is adjustable in order to adjust the sieving stroke and/or sieve throwing angle, the eccentric device comprising: - an input shaft, which input shaft has a center line, - a flange, which is fixedly connected to the input shaft in order to rotate along with said input shaft around the center line of said input shaft, - a gear, which is provided with a toothing around its outer circumference, which gear is rotatably mounted onto the flange, the rotation axis of said gear being non-coaxial with respect to the center line of the input shaft, - an output shaft, which is fixedly connected to said gear in order to rotate along with said gear around the rotation axis of said gear, - an annular gear, which annular gear has a toothing on its inner diameter and on its outer diameter, the toothing on the inner diameter of the annular gear engaging the toothing on the outer circumference of the gear, - said annular gear being stationary during normal operational use of the sieve drive assembly, - an adjustment gear, which is stationary during normal operational use of the sieve drive assembly, which adjustment gear is provided with toothing on its outer circumference, which toothing engages the toothing on the outer diameter of the annular gear. - a rotary drive, which rotary drive comprises a rotatable output shaft, - a transmission that provides a connection between the rotatable output shaft of the rotary drive and the sieve, which transmission is adapted to transform a rotational movement of the rotatable output shaft into the reciprocating sieve movement of the sieve, - an input shaft, which input shaft has a center line, - a flange, which is fixedly connected to the input shaft in order to rotate along with said input shaft around the center line of said input shaft, - a gear, which is provided with a toothing around its outer circumference, which gear is rotatably mounted onto the flange, the rotation axis of said gear being non-coaxial with respect to the center line of the input shaft, - an output shaft, which is fixedly connected to said gear in order to rotate along with said gear around the rotation axis of said gear, - an annular gear, which annular gear has a toothing on its inner diameter and on its outer diameter, the toothing on the inner diameter of the annular gear engaging the toothing on the outer circumference of the gear, - said annular gear being stationary during normal operational use of the sieve drive assembly, - an adjustment gear, which is stationary during normal operational use of the sieve drive assembly, which adjustment gear is provided with toothing on its outer circumference, which toothing engages the toothing on the outer diameter of the annular gear.