A device and method for retaining the position of a core in a casting mold, such as a vehicle cylinder head casting mold. The core may be a port core, such as an exhaust port core. A plunger assembly is arranged in the mold to produce a substantially unidirectional pressing force against a supported end of the core. Due to the shape of the core and its orientation and arrangement with respect to the mold, the substantially unidirectional force exerted by the pin also creates a moment that results in an additional pressing force component that is substantially perpendicular to the direction of the pressing force exerted by the pin. This second force component presses contacting ends at the other end of the core into tight contact with an associated molding surface. Consequently, the plunger assembly produces a retention force on the core in two directions.