All About Engines

The Petrol Motor 227 The mode of operation was as follows: The crank case was enclosed and supplied with air and petrol from the carburettor. As each piston (by the motion of the cylinders) was withdrawn, the air and petrol passed through a valve in the head of the piston into the cylinder. On the return of the piston (again by the motion of the cylinders) the mixture was compressed, and since more room for the ex- panding gases could only be provided by the rota- tion of the cylinders, that motion was encouraged. As the piston again approached the closed end of the cylinder the exhaust valve in that end opened and the waste gases were swept out. The cycle was, therefore, a four-stroke one. The chief advantage of this engine was its extreme lightness — a little over 2 lb. per horse-power. In fact, the weight of a 100 horse-power engine was only 220 lb. The cylinders were not water-jacketed, as the rapid motion through the air kept them suffi- ciently cool. They were of steel, turned and bored out of solid cylinders so that the sides were only I inch in thickness, with “ fins ” on the outer surface, to increase the cooling effect. The rotating cylinders themselves served as a flywheel, giving a remarkably steady effect. It occupied a very small space, the 80 horse-power seven-cylinder type being only about 2 feet 6 inches in diameter and less than i foot from back to front at the thickest part. Against these advantages there were certain ob- jections. The lubricating oil in the crank chamber was flung outwards by centrifugal force, and passed