The bushing into which the spark plug screws is not integral with the cylinder as in a cast construction, but is welded into the side of the cylinder head by means of the autogenous process. It is also evident that this construction enables the inlet valves to be easily removed, since these screw into the piston head. Both inlet and exhaust valves in the Gnome engine are removed with the greatest ease, special socket wrenches being supplied for the purpose. The castor oil, which is used as a lubricant, and the gasoline, are fed by a positive acting piston pump to the hollow crank shaft. The lubricant and fuel then pass through the automatic inlet valve in the head of the cylinder. [Illustration: Fig. 55. Gnome Motor Running On Test Stand. From Scientific American. ] The spark produced by the high tension magneto is led to the proper cylinder through a brush that presses on a revolving ring of insulating material in which is imbedded 7 metallic segments, one of the segments being connected to a corresponding cylinder. As the distributor ring revolves the segments come into contact with the brush in the proper order. The magneto is stationary and is supported by a bracket in an inverted position. A pinion on the magneto shaft meshes with a large gear mounted on the revolving crank case so that the armature of the magneto always bears a positive relation to the piston position. As the engine requires seven sparks for every two revolutions, or 3½ sparks per revolution it is evident that the magneto must turn 1.75 times as fast as the engine, if the magneto is of the ordinary type that generates two sparks per revolution. In other words the magneto speed is to the engine speed as 7 is to 4. [Illustration: The “Indian” Rotary Aero Motor. ] The arrangement of connecting rods is interesting, the big end of one rod being formed into a cage for the reception of the crank-pin ball race. The outer circumference of the cage carries the pins to which the other six connecting rods are fastened. It is necessary that one rod be integral with the cage to prevent its rotation in regard to the cylinders. Annular ball bearings are used on both the main bearings, for the thrust bearing to take the thrust of the propeller, and on the large end of the master connecting rod. The large ends of the auxiliary connecting rods and the small ends of all the rods have plain bearings. CHAPTER VI TWO STROKE CYCLE ENGINES (30) The Junker Two Stroke Cycle Engine.