An injection molding apparatus includes a back plate, a driven pulley connected to the back plate and rotatable with respect to the back plate, a screw connected to the driven pulley to rotate with the driven pulley, a motor having an attached drive pulley, a belt or chain coupling the driven pulley and the drive pulley, a valve pin plate, a nut connected to the valve pin plate and mated with the screw, at least one valve pin connected to the valve pin plate, a manifold fixed with respect to the back plate, and at least one nozzle connected to the manifold. The valve pin extends through the nozzle to control flow of molding material. The screw can be a ball screw and nut can be a ball nut. The screw can have one portion connected to the driven pulley and another portion connected to a mold plate in a rotatable manner. The valve pin plate may be an assembly with an upper plate, a lower plate, and at least one valve pin holder fixed between the upper plate and the lower plate, the valve pin being fastened to the valve pin plate assembly with the valve pin holder. The positions of the screw and nut can be reversed.