GB733114A - - Google Patents

Abstract

733,114. Sparking plugs. LODGE PLUGS, Ltd. June 8, 1954 [June 8, 1953], No. 15688/53. Classes 7(2) and 7(4). In a sparking plug wherein the sparking end 11 of the metallic body is adapted to project into or. communicate with the combustion chamber between the valve seats, the end 11 is left unthreaded and has a diameter not greater than 7 mm. but preferably of the order of 5 mm. or less and a length of 5 mm. or more, the body being adapted for connection to the chamber solely by means of a threaded part 12 of considerably greater diameter behind the sparking end. The body is formed of two parts 10, 11, the latter being plain and comprising a small diameter part 16 below the threads 12 that supports the earth electrode 17 which is spaced from the central electrode 18 mounted in an insulator 19 ; the part 16 incorporates a shoulder from which upstands a cylindrical portion 20 accommodating the insulator, the upper end of the portion 20 being out-turned to abut a shoulder 21 in the part 10. The latter thereby supports the part 11 and permits of play therebetween for alignment purposes ; the shoulder on the part 11 co-operates with a seating in the cylinder head to form a gas-tight joint when the plug is mounted on an engine. Because of its small diameter firing end the plug may be located on the central axis of a combustion chamber with the active end of the electrodes either within or flush with the chamber without causing fracture of the metal between the valve seatings whilst permitting the use of valves of maximum possible diameter.