Fig. 70.—Wiring Diagram of Dixie Magneto Installation on Hall-Scott Six-Cylinder 125 Horse-Power Aeronautic Motor.
Fig. 71.—How Magneto Ignition is Installed on Thomas-Morse 135 Horse-Power Motor.
SPARK-PLUG DESIGN AND APPLICATION
With the high-tension system of ignition the spark is produced by a current of high voltage jumping between two points which break the complete circuit, which would exist otherwise in the secondary coil and its external connections. The spark-plug is a simple device which consists of two terminal electrodes carried in a suitable shell member, which is screwed into the cylinder. Typical spark-plugs are shown in section at [Fig. 72] and the construction can be easily understood. The secondary wire from the coil is attached to a terminal at the top of a central electrode member, which is supported in a bushing of some form of insulating material. The type shown at A employs a molded porcelain as an insulator, while that depicted at B uses a bushing of mica. The insulating bushing and electrode are housed in a steel body, which is provided with a screw thread at the bottom, by which means it is screwed into the combustion chamber.
Fig. 72.—Spark-Plug Types Showing Construction and Arrangement of Parts.