Abstract: A self-propelled drilling head comprises a base section including gripper shoes mounted for extension and retraction to selectively grip the wall of a hole being drilled. A first actuator is provided for extending and retracting the gripper shoes. A drilling section is mounted on the base for reciprocation relative thereto. A second actuator is provided for urging the drilling section downwardly relative to the base section when the gripper shoes are extended. A cutter bit is mounted at a lower end of the drilling section. A third actuator is provided for rotating the cutter bit and comprises a first hydraulic motor having a first output shaft. A second hydraulic motor is spaced below and laterally offset from the first hydraulic motor and has a second output shaft extending parallel to the first output shaft. A driven gear is mounted at the end of each output shaft. A drive transmitting gear mechanism is meshingly engaged on opposite sides by the driven gears.