A sieve (142) for a cleaning system (140) of an agricultural harvester (100) includes a sieve frame (201) defining a top side (204)； a plurality of adjustable louvers (202) carried by the sieve frame (201) and defining a plurality of apertures (203)； and at least one adjustment bar (310) coupled to the plurality of adjustable louvers (202) such that displacement of the at least one adjustment bar (310) changes a size of at least some of the plurality of apertures (203). The sieve (142) also includes an adjustment assembly (220) including an adjustment arm (221) coupled to the at least one adjustment bar (310) and pivotable relative to the sieve frame (201) such that pivoting of the adjustment arm (221) about a pivot axis (PA) displaces the at least one adjustment bar (310). The adjustment arm (221) carries a locking pin (324) that is displaceable between a locking position where the adjustment arm (221) is not freely pivotable about the pivot axis (PA) and an adjustment position where the adjustment arm (221) is freely pivotable about the pivot axis (PA). A shaft (340, 640) is disposed on the top side (204) and coupled to the adjustment arm (221). The shaft (340, 640) is displaceable such that displacement of the shaft (340, 640) from a first position to a second position causes a corresponding displacement of the locking pin (324) from the locking position to the adjustment position.
