Abstract: A pneumatic hammer drill includes a tool connected to a pneumatic cylinder having an air valve assembly, return- and forward-stroke chambers, a piston, and a connecting passage interconnecting fluidly the return- and forward-stroke chambers. When the piston approaches the tool, the connecting passage permits air to flow from the return- to the forward-stroke chamber so that the pressure in the return-stroke chamber is reduced, and the speed of a forward stroke of the piston is increased. When the piston approaches the air valve assembly, the connecting passage permits air to flow from the forward- to the return-stroke chamber so as to reduce the pressure in the forward-stroke chamber so that the piston moves close to the air valve assembly during a return stroke thereof and the length of the forward stroke is increased.