Forage harvester

A forage harvester cracker unit comprising a base frame comprising left and right hand side elements, a first cracker roller being mounted on the base frame to be rotatable about a fixed central axis extending between the left and right hand side elements of the base frame and a secondary frame comprising left and right hand side elements, a second cracker roller being mounted on the secondary frame to be rotatable about a central axis extending between the left and right hand side elements of the secondary frame, wherein the forage harvester cracker unit further comprises an axle extending between the left hand side elements of the base frame and the secondary frame and the right hand side elements of the base frame and the secondary frame forming a pivot axis extending through the base frame and the secondary frame, the secondary frame being adjustable about the pivot axis to enable variation of a separation of the first and second cracker rollers, a biasing element acting between the base frame and the secondary frame to urge the second cracker roller towards the first cracker roller and a drive element acting against the biasing element to hold the secondary frame in position against the biasing element to maintain a minimum separation of the first and second cracker rollers characterised in that the drive arrangement comprises includes a drive shaft parallel to but offset from the axle and supported for rotation in bearings provided in the left and right hand side elements of the base frame, parallel levers eccentrically mounted on the left and right hand sides of the drive shaft at a proximal end of each of the parallel levers, a distal end of each parallel lever being retained within respective left and right hand side elements of the secondary frame so that rotation of the drive shaft about its axis results in movement of the secondary frame with respect to the base frame and the distance between the first and second cracker rollers to be varied, the drive arrangement further comprising an actuator to control rotation of the drive shaft.