Abstract: A mold assembly for molding lightweight pistons having weight reduction pockets formed in outer surfaces thereof above pin holes. The weight reduction pockets are formed using window structures that are movable upward and downward at inclined angles. The movement of the windows is coordinated with the movement of pin members that are used to form the pin holes, which pin members pass through the windows. The movement of the windows and pin members is controlled by a cam assembly that uses an elongate cam element that moves horizontally and affects upward and downward movement of the windows.