Abstract: A spark plug for an internal combustion engine is provided which includes a metal shell, a porcelain insulator, a center electrode, and a ground electrode. The center electrode is retained in the porcelain insulator to define a spark gap between itself and the ground electrode. The porcelain insulator has a nose made up of an upright portion and a tapered portion continuing from the upright portion toward a top end thereof. The tapered portion has a diameter decreasing toward the top end of the porcelain insulator. The upright portion has an outer wall extending substantially parallel to an inner wall of the metal shell, thereby inducing the formation of side sparks between the tapered portion and the metal shell before the insulation resistance between the center electrode and the metal shell drops, thereby giving a signal indicative of such an event to an operator.

Abstract: A spark plug for an internal combustion engine is provided which includes a metal shell, a porcelain insulator, a center electrode, and a ground electrode. The center electrode is retained in the porcelain insulator to define a spark gap between itself and the ground electrode. The porcelain insulator has a nose made up of an upright portion and a tapered portion continuing from the upright portion toward a top end thereof. The tapered portion has a diameter decreasing toward the top end of the porcelain insulator. The upright portion has an outer wall extending substantially parallel to an inner wall of the metal shell, thereby inducing the formation of side sparks between the tapered portion and the metal shell before the insulation resistance between the center electrode and the metal shell drops, thereby giving a signal indicative of such an event to an operator.

Abstract: A spark plug structure produces sparks between a second ground electrode and a center electrode when a porcelain insulator is stained with carbon. A wear resisting member is installed on a side wall of the center electrode for minimizing the wear of the side wall caused by the sparks to increase the useful life of the spark plug. A production method is also provided.

Abstract: At least one of a center electrode and a ground electrode of an engine spark plug is a Ni-base alloy containing, in weight percentage, 0.5˜2.5% Si, 0.1˜1.2% Mn, 3.2˜5.0% Al, 0.9˜2.8% Cr, 0.001˜0.025% C in addition to Ni and unavoidable impurities. And, a value S/V is in a range from 1.7 mm−1 to 3.9 mm−1 when ‘S’ represents a surface area of the ground electrode and ‘V’ represents a volume of the ground electrode.

Abstract: A first gap discharge gap is located between a front end of a center electrode and a front side of a first ground electrode of a spark plug. A second discharge gap is located between a front end of a second ground electrode and a front side of the center electrode. Respective dimensional relationships between various of these elements are established to promote self-cleaning of the spark plug.

Abstract: At least one of a center electrode and a ground electrode of an engine spark plug is a Ni-base alloy containing, in weight percentage, 0.5˜2.5% Si, 0.1˜1.2% Mn, 3.2˜5.0% Al, 0.9˜2.8% Cr, 0.001˜0.025% C in addition to Ni and unavoidable impurities. And, a value S/V is in a range from 1.7 mm−1 to 3.9 mm−1 when ‘S’ represents a surface area of the ground electrode and ‘V’ represents a volume of the ground electrode.

Abstract: An improved structure of a spark plug in which sparks are produced between a second ground electrode and a center electrode when a porcelain insulator is stained with carbon is provided. A wear resisting member is installed on a side wall of the center electrode for minimizing the wear of the side wall caused by the sparks to increase the useful life of the spark plug. A production method is also provided.

Abstract: In a spark plug having a center electrode, first and second ground electrodes, an insulator and a metal housing, a first discharge gap is constituted between a front end of the center electrode and a front side of the first ground electrode and a second discharge gap is constituted between a front end of the second electrode and a front side of the center electrode. Respective dimensional relationships of A, B, C, H, F and L1 are defined where A is a distance of the first discharge gap, Bis a shortest distance between the front end of the second ground electrode and the insulator, C is an axial length from a leading end of the metal housing and a front end of the insulator, H is an axial length from the front end of the insulator and the front end of the center electrode, F is an axial length from the front end of the insulator to the front end edge of the second electrode and L1 is a shortest axial length from the leading end of the metal housing to the front end of the second ground electrode.

Abstract: A coating layer made of a heat-proof insulating material is formed on the surface of a leg, exposed to the interior of the engine, of a ceramic insulator of a sparking plug. The coating is formed of a mixed solution of silicone oil blended with a mixture of parafin and ozokerite. The mixed solution contains 100 weight percent of silicone oil blended with paraffin by at least 5 weight percent and ozokerite by at least 0.2 weight percent.