Patent ID: 8896192

Claim:
A method of manufacturing a spark plug, the spark plug including a tubular metallic shell extending in an axial direction; a tubular insulator provided inside the metallic shell; a rod-like center electrode provided inside the insulator and positioned coaxial with the metallic shell; and a ground electrode whose base end portion is joined to a front end face of the metallic shell and which forms a gap between a distal end portion thereof and the center electrode, the manufacturing method comprising: assembling together the metallic shell and a center electrode assembly including the insulator and the center electrode provided therein; and joining the ground electrode to the front end face of the metallic shell after the assembling step, wherein the distance between a plane perpendicular to the axis and the front end face of the metallic shell as measured along the axis continuously varies around the entire front end face in a circumferential direction of the metallic shell; and the joining step comprises adjusting the position of a distal end portion of the ground electrode relative to the front end portion of the center electrode assembly along the axis by changing a region of the front end face of the metallic shell to which the ground electrode is joined.