Flywheel magneto rotor and manufacture method thereof

A rotor of a flywheel magneto comprising a boss rigidly mounted on a driving shaft, and a flywheel joined to the boss and carrying thereon a plurality of permanent magnets, wherein the improvement comprises:

• a joining portion of the boss including a cylindrical surface, and an annular groove formed in the cylindrical surface and having a rugged bottom and two sides, one of which is inclined so that metal flow along the inclined side can be effected;
• a joining portion of the flywheel including an inner face of a hole made in the flywheel for inserting the boss, and an annular groove made in the inner face of the hole and shaped similarly to the groove of the boss, the inner face of the hole being spaced from the cylindrical surface by a predetermined distance, and
• a joining member filled in an annular gap defined by both the joining portions of the boss and the flywheel through metal flow thereof and having a form imported by the annular gap, the form providing the joining member with approximately the same shearing strength as that of the joining portion of the flywheel.