Method for producing water jacket spacer

A method for producing a water jacket spacer that is assembled into the inside of a water jacket provided in a water-cooled internal combustion engine in order to control the flow of cooling water, wherein

• the water jacket spacer has a side wall part in which a plurality of arc-like peripheral surface parts are connected through one or more waist parts;
• a prescribed resin material is injection molded by using a molding die for injection molding which is configured to form an inner peripheral surface of the water jacket spacer by a mold piece wherein a draft angle of the inner peripheral surface of the water jacket spacer is a fixed angle along a mold-opening direction without any mold partition line on the inner peripheral surface and wherein resin flow channels are provided so that a plurality of gates are arranged along the longitudinal direction at a position corresponding to an outer peripheral surface of the side wall part and corresponding to the arc-like peripheral surface parts or the one or more waist parts;
• the inner peripheral surface of the water jacket spacer being a surface facing a bore wall of the water-cooled internal combustion engine when the water jacket spacer is assembled into the inside of the water jacket,
• the outer peripheral surface of the side wall part being a surface of the side wall part opposite a surface of the side wall part facing the bore wall of the water-cooled internal combustion engine when the water jacket spacer is assembled into the inside of a water jacket;
• and
• after mold opening and ejecting, cooling is done while leaving a runner being connected to the gates in a shape of a teeth of a comb, and thereafter, the runner is cut off.