Insert core and method for manufacturing a cylinder for internal combustion engine by making use of the insert core

A method of manufacturing a cylinder for an internal combustion engine, which is featured in that the cylinder is manufactured by a die casting method by making use of an insert core adapted for manufacturing a cylinder provided with an inner wall-attached hollow scavenging passageway having a scavenging port to be opened and closed by the movement of a piston, the insert core comprising:

• a cylindrical body having substantially the same outer diameter as the diameter of bore of the cylinder to be obtained;
• a scavenging port-forming portion projecting radially outward from the cylindrical body and having substantially the same cross-sectional configuration as that of the scavenging port;
• a suction port-forming portion projecting radially outward from the cylindrical body and having substantially the same cross-sectional configuration as that of at least the cylinder bore-side end portion of a suction port;
• and
• an exhaust port-forming portion projecting radially outward from the cylindrical body and having substantially the same cross-sectional configuration as that of at least the cylinder bore-side end portion of an exhaust port;
• the method comprising:
• externally attaching the insert core to a bore-core die, the bore core die being capable of repeated use;
• using the resultant casting die, cast molding a raw cylinder body with the insert core remaining therein;
• subjecting the resultant raw cylinder body to boring for forming a cylinder bore to remove a cylindrical portion of the insert core;
• and
• removing by making use of a press the scavenging port-forming portion, suction port-forming portion and exhaust port-forming portion of the insert core, which remain in the raw cylinder body;
• wherein the bore core die includes a columnar portion adapted to receive the cylindrical body of the insert core.