Patent ID: 8087961

Claim:
A method of producing a spark plug, comprising in steps: (a) preparing a semi-finished spark plug unit, the unit comprising a center electrode that has a leading end portion, a cylindrical insulator that has an axial bore to install therein the center electrode except the leading end portion, a cylindrical metal shell that holds therein the cylindrical insulator and a ground electrode that has one end fixed to a leading end of the cylindrical metal shell; (b) bending the ground electrode so that a bent front portion of the ground electrode projects toward the leading end portion of the center electrode; (c) putting an electrode tip on a given part of the bent front portion of the ground electrode in such a manner that a front portion of the electrode tip projects from the bent front portion toward the leading end portion of the center electrode; (d) welding the electrode tip to the given part of the bent front portion of the ground electrode; (f) moving a spacer jig to a position between the electrode tip and the leading end portion of the center electrode; and (g) contacting the spacer jig to the leading end portion of the center electrode and contacting the electrode tip to the spacer jig, in which the spacer jig comprises: a first stopper portion that contacts the electrode tip to restrain movement of the electrode tip in a direction perpendicular to both an axial direction of the semi-finished spark plug unit and a direction in which the electrode tip projects; and a second stopper portion that contacts the center electrode to restrain movement of the spacer jig in the direction perpendicular to both the axial direction of the semi-finished spark plug unit and the direction in which the electrode tip projects.