Abstract: The disclosure relates to the drive and rotation speed adjustment for a threshing rotor of rotary grain harvesters. The technical result, intended to be achieved by the invention, is an improvement in the reliability of the rotor drive due to its design simplification, an increase of torque transferred from the engine to the rotor and assured regulation of the speed of the stepless rotor. The technical result is obtained by including a hydraulic cylinder, ratchet wheel and lock, wherein the hydraulic cylinder installed on the rotor drive gearbox housing controls lock blocking of the ratchet wheel by a mechanical linkage, and the ratchet wheel is fixed with a shall of the inside planetary gear. Selection of transfer ratios for gearbox gears allows the harvester weight to be reduced by excluding the transmission gear box from the rotor drive gearbox.