Piston.—The disc which slides up and down in the cylinder, and communicates the force of the explosion to the connecting-rod and crank.
Piston Rings.—Cast-iron split rings, fitted in grooves round the piston to make a gas-tight joint between the piston and the walls of the cylinder.
Pressure Feed.—See Feed.
Radiator.—A device for cooling the water circulating round the cylinders by exposing it to a large surface in contact with free air.
Side-Slip.—An accident liable to occur on greasy roads, but of less frequent occurrence since the introduction of “non-skidding” devices.
Silencer.—A box or chamber designed to reduce the noise caused by the escape of the exhaust gases.
Spares.—Duplicate parts of machinery carried in case of a breakdown.
Sparking-plug.—A porcelain plug, carrying the electric wires, which is screwed into the combustion chamber of the cylinder. At the end of the plug within the cylinder are platinum points in connection with the wires. The current jumping from point to point makes the spark which fires the charge.
Throttle.—The control of the volume of mixture supplied to the engine.