Page:Motors and motor-driving (1902).djvu/167

Rh cooling medium, a continuous coil or battery of piping is placed on the front of the car, where it is most exposed to the current of air produced by the car in travelling. Through this coil the heated water is forced by the pump, the heat being carried off from the surface of the pipes by the air. In order to increase the radiation from the pipes, the area of the surface exposed to the air is increased by fitting flanges of thin metal in intimate connection with the pipes, or by originally forming the pipes with these flanges in the solid. Woven wire-work is also used, soldered to the pipes, with the same object.

The crank chamber, or base chamber, as it is usually termed, forms the base of the cylinder. Its use for lubricating purposes is very important. About half a pint of oil is kept at the bottom of this chamber, into which the crank dips at every revolution, thereby splashing up oil which lubricates the wristpin, gudgeon-pin, crank bearings, crank-shaft bearings, the sides of the cylinder and the piston-rings. The lubrication of the latter is, of course, assisted by special oilers, which will be referred to later.

The piston used in motor-cars is generally known as the trunk type. It is composed of an iron casting which is made a good sliding fit in the cylinder; around its upper end three or four square-bottomed grooves are cut, and in these the piston-rings fit. The rings are made of cast iron, and the bore being eccentric to its outer diameter, there is a certain amount of spring in them, and so a gentle pressure is kept against the cylinder, preventing any of the expanding gases passing the piston. The piston is made to balance the crank.

Needless to say, the lubrication of the piston rings is of very vital importance, for on that depends the free working of the piston in cylinder. In single-cylinder engines, they