Abstract: An air precleaner for an internal combustion engine includes an outer cylindrical casing with a top air intake opening and a set of stationary vanes within the casing which impart a centrifugal motion to air entering the casing. A clean air discharge tube positioned centrally within the casing extends from an upper air inlet below the vanes through a frusto-conical bottom of the casing to a connection with the conventional air filter of the engine. The bottom wall of the casing includes a generally radially extending slot, the upstream edge of which is offset downwardly from the downstream edge to discharge dirt-laden air from outer portions of the casing back to the atmosphere while cleaner air at central portions of the casing is drawn by engine suction through the discharge tube and air filter into the engine.