A mold opening and closing mechanism includes an aligning mechanism which has a horizontal mounting plate including a number of vertical openings for the number of molds, that is supported by a pair of spaced vertical uprights secured to the section frame top surface. A plurality of aligning cylinders are located in the vertical openings in the horizontal mounting plate and move parallel with the mold holder motion. Each cylinder includes surfaces configured to mate with the clamping surfaces of the mold holders. The axis of one of the aligning cylinders is held but not clamped at the theoretical centerline so it can move to the actual centerline when the mold holders are located at the advanced clamped closed position. A position transducer is mounted parallel with the mold holder motion to sense movement of the axis of one of the aligning cylinders and a computer receiving positional data from the transducer compares the theoretical centerline with the actual centerline determined from the data and defines a displacement offset for the displacement program to align the mold holders to the theoretical centerline.