Abstract: A tool for installing valve stems in the rims for tubeless tires from the outside of the rim. The tool includes a cylindrical barrel having a tip for insertion in the opening in the rim, the interior walls of the barrel converging toward the tip end. The barrel is removably affixed to an actuating mechanism including a push rod adapted to be advanced and retracted within the barrel. The forward end of the push rod has an internally threaded fitting for mating with the threaded end of conventional tubeless tire valve stems. The actuating mechanism may be operated to incrementally advance the push rod, and thereby a valve stem affixed thereto, along the converging barrel to eject the valve stem through the barrel tip and seat it within the opening in the rim. An indicia may be provided on the push rod for visually indicating the axial position of the valve stem.