Abstract: A burrowing tool having a pneumatically reciprocable piston hammer concentrically slidable about an adjustable valve sleeve, wherein the valve sleeve may be positioned to cause the piston hammer to impact against either a forward or a rearward anvil, with position mechanism including a threaded and slotted reversing screw removably fitted into the rearward end cap of the tool, the slotted portions of the reversing screw serving as a plurality of exhaust ports, wherein the end cap is sized to permit removal of the valve and inner mechanism upon removal of the reversing screw from the tool.