Patent ID: 7901262

Claim:
A method of manufacturing a spark plug for an internal combustion engine, the method comprising the steps of: (a) preparing a tubular metal shell, an insulator, a center electrode, and a ground electrode; (b) assembling the metal shell, the insulator, and the center and ground electrodes together, so that the metal shell holds therein the insulator, the center electrode is secured in the insulator, and the ground electrode is fixed to the metal shell to form a spark gap between the center and ground electrodes; and (c) adjusting the spark gap to bring the size of the spark gap into agreement with a target value, wherein in the step (c), the ground electrode is repeatedly pressed, by a hammer, toward the center electrode from a state where the size of the spark gap is greater than a predetermined value that is greater than the target value, the hammer operates in a first mode when the size of the spark gap falls in a rough-process range which is above the predetermined value, and in a second mode when the size of the spark gap falls in a finish-process range which is between the target value and the predetermined value, and the amount of pressing the ground electrode in any press stroke of the hammer in the second mode is less than the amount of pressing the ground electrode in any press stroke of the hammer in the first mode, wherein the amount of pressing the ground electrode in every press stroke of the hammer in the second mode is equal to a fixed value, and wherein in both the first and second modes, the hammer is returned, after each press stroke, to a return position, and all the return positions of the hammer are different from one another.