Abstract: An in-hole rock drilling machine has a hydraulic impact motor within a housing. The hydraulic impact motor has a spool valve contained within a valve housing. The spool valve has two operating positions to alternately pressurize and depressurize a drive chamber to reciprocate a hammer. The spool valve has a continuously pressurized third control surface that biases the spool valve towards a second operating position, a first control surface that acts opposite the third control surface to move the spool valve to a first operating position, and a second control surface that acts with the third control surface to return the spool valve to the second operating position. The valve housing guides the rear portion of the hammer, and a guide bushing guides the front portion of the hammer. The guide bushing, valve housing, and a distance sleeve are clamped against a shoulder of the housing.