Abstract: There is disclosed an hydraulic drilling motor for well drilling. The motor is of the push-down axial flow type. It is of vibration-free rotary chamber-type construction functioning with high torque wherein the r.p.m. and capacity of the drilling tool are in proportion with the velocity and pressure of the flowing medium. The motor consists of an internally threaded chamber with an arch parallel with the flow direction of an externally threaded spindle of z.sub.o =z.sub.k (arch or thread)+1, or z.sub.o =z.sub.k -1 thread, of identical course with the chamber, arranged in the chamber. The cross section of the spindle or chamber is prolate, peaked or curate cycloid. When the spindle is cycloid cross sectional, the cross section of the chamber is in the same plane, and when the chamber is in cycloid cross sectional the cross section of the spindle is in the same plane. This is limited by the external or internal envelope curve of the surface touched by the cycloid during relative motion.