Abstract: Cylinder block molding apparatus includes two series of parallel and alternate molding plates for partitions. The plates extend in planes perpendicular to the axis of an engine shaft. Each series of molding plates is mounted, respectively, on a support capable of sliding parallel to the axis of the engine shaft relative to the cylinder block between a molding position where mutually confronting molding faces of two consecutive plates bear against one another and a lifting position where the molding faces are moved apart as a result of sliding of the supports.