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

There is provided a method for manufacturing a cylinder for an internal combustion engine by making use of an insert core, which makes it possible to manufacture the cylinder by a die casting method such as a high-pressure die casting method at low cost and in high accuracy. The insert core to be employed herein includes: 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.