Powered hammer

A powered rotary hammer or chisel hammer has a hammer mechanism with a ram (20) reciprocatingly movably mounted in a guide tube section (15) and comprising an outer circumferential surface in which a vent channel (24) is provided which connects the front end of the circumferential surface with its rear end and which is interrupted by a radially outwardly projecting sealing portion (22), and has a piston (13) reciprocatingly drivable by means of a motor of the hammer which piston in operation generates a varying air cushion between the ram (20) and the piston surface facing the ram to cause an impact on the tool bit inserted into the tool holder (10) of the hammer by movement of the ram (20) towards the tool bit wherein the space between the ram (20) and the surface of the piston (13) facing the ram (20) is temporarily connected to ambient air through the vent channel (24) after causing the impact. The vent channel (24) on the outer circumferential surface of the ram (20) is helically shaped.