An agricultural harvester, comprising: a chassis; a threshing and separating assembly carried by said chassis; and a chopper assembly carried by said chassis that receives crop material from said threshing and separating assembly, said chopper assembly including: at least one movable chopping knife; a plurality of counter knives movable between a first knife position and a second knife position, said plurality of counter knives configured to cooperate with said at least one chopping knife to cut crop material when in said first knife position; a shear bar movable between a first bar position and a second bar position; and a linkage assembly connected to said plurality of counter knives and said shear bar such that said linkage assembly is selectively actuable to simultaneously move said plurality of counter knives between said first knife position and said second knife position and said shear bar between said first bar position and said second bar position, the linkage assembly including a pivotable knife arm linked to said plurality of counter knives and a pivotable bar arm (112, 164) linked to said shear bar, wherein pivoting of said knife arm moves said plurality of counter knives between said first knife position and said second knife position and pivoting of said bar arm (112, 164) moves said shear bar between said first bar position and said second bar position, and characterized in that said linkage assembly includes an engagement cam (116, 116A, 116B, 162) that is rotated by a shaft and that engages at least one surface (118, 168A, 168B, 168C, 168D) of said bar arm (112, 164). a chassis; a threshing and separating assembly carried by said chassis; and a chopper assembly carried by said chassis that receives crop material from said threshing and separating assembly, said chopper assembly including: at least one movable chopping knife; a plurality of counter knives movable between a first knife position and a second knife position, said plurality of counter knives configured to cooperate with said at least one chopping knife to cut crop material when in said first knife position; a shear bar movable between a first bar position and a second bar position; and a linkage assembly connected to said plurality of counter knives and said shear bar such that said linkage assembly is selectively actuable to simultaneously move said plurality of counter knives between said first knife position and said second knife position and said shear bar between said first bar position and said second bar position, the linkage assembly including a pivotable knife arm linked to said plurality of counter knives and a pivotable bar arm (112, 164) linked to said shear bar, wherein pivoting of said knife arm moves said plurality of counter knives between said first knife position and said second knife position and pivoting of said bar arm (112, 164) moves said shear bar between said first bar position and said second bar position, and at least one movable chopping knife; a plurality of counter knives movable between a first knife position and a second knife position, said plurality of counter knives configured to cooperate with said at least one chopping knife to cut crop material when in said first knife position; a shear bar movable between a first bar position and a second bar position; and a linkage assembly connected to said plurality of counter knives and said shear bar such that said linkage assembly is selectively actuable to simultaneously move said plurality of counter knives between said first knife position and said second knife position and said shear bar between said first bar position and said second bar position, the linkage assembly including a pivotable knife arm linked to said plurality of counter knives and a pivotable bar arm (112, 164) linked to said shear bar, wherein pivoting of said knife arm moves said plurality of counter knives between said first knife position and said second knife position and pivoting of said bar arm (112, 164) moves said shear bar between said first bar position and said second bar position, and characterized in that said linkage assembly includes an engagement cam (116, 116A, 116B, 162) that is rotated by a shaft and that engages at least one surface (118, 168A, 168B, 168C, 168D) of said bar arm (112, 164).