The magnitude of the diametrical gap, as a parameter that determines the service life of the pressure block, is determined by the geometric error of the toothed surface of its outer rotor. Analysis of literary sources shows that the issue of increasing the service life of the pressure block of a planetary hydraulic motor remains unsolved and is, therefore, a relevant scientific area. The studies showed that for a serial external unit, the shape error is E = 0.12…0.18 mm due to its manufacturing technology. The proposed design of the modernized external rotor ensures an error in the shape of its toothed profile within the limits of E = 0.03…0.06 mm due to changes in manufacturing technology. Changing the design of the external rotor made it possible to significantly reduce the error in the shape of the gear profile during manufacturing. It has been established that the critical value of the diametrical gap Gd of the serial pressure block equals Gd = 0.12 mm. For the modernized pressure block, it is equal to Gd = 0.37 mm, which increases the service life of the pressure block of the planetary hydraulic motor by more than three times.