Abstract: A sieve assembly for separating grain from chaff inside of a combine. The sieve assembly comprises a plurality of longitudinal sieve planks that pivot on their longitudinal axis. A hanging weighted member combined with the sieve planks regulates the angle of the sieve planks relative to the combine. As the combine becomes laterally inclined on a hillside, the weighted member changes its angular position relative to the combine. In doing so, the weighted member causes the sieve planks to pivot on their longitudinal axis so that the sieve planks remain level relative to the horizon. Dividers extend between each sieve plank.