Abstract: A forage harvester has a rotary cylinder type cutterhead mounted in a housing with opposite side walls, crop material being fed into the cutterhead in a generally radial direction over a shear bar adjacent the cutterhead periphery. The shear bar is mounted for fore and aft adjustment toward and away from the cutterhead periphery to maintain the optimum clearance between the cutterhead and the shear bar by means of a mechanism that includes a pair of bell cranks respectively pivotally mounted to support members on the opposite walls, with one end of each bell crank being connected to the shear bar through a fore and aft link while the other end of the bell crank threadably receives the threaded portions of a vertically elongated rod that is rotatably supported adjacent the housing side wall and has an easily accessible head adjacent the top of the housing, whereby rotation of the rod causes the bell crank to rock on its pivot to cause linear fore and aft adjustment of the shear bar.