Spark plug and method of manufacturing the same

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.