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Fig. 8.—Plan View of the Dort Four Cylinder Chassis, Showing Im.
portant parts of the Mechanism and Their Relation to Each Other.
mittent pushes on the piston head produced by the explosion of the gas in the cylinder. If some explosive is placed in the chamber formed by the piston and closed end of the cylinder and exploded, the piston would be the only part that would yield to the pressure which would produce a downward movement. As this is forced down the crankshaft is turned by the connecting rod, and as this part is hinged at both ends it is free to oscillate as the crank turns, and thus the piston may slide back and forth while the crankshaft is rotating or describing a curvilinear path. It is imperative that flywheels be attached firmly to the crankshaft, because any looseness between the flywheel and the shaft will produce a pronounced knocking sound, and the methods of fastening, such as keys or bolts, may be entirely sheared off.
The marks on flywheel rims are placed thereon to assist in timing the valves and ignition spark. The abbreviation E. O. means "Exhaust Opens,” while E. C. means “Exhaust Closes.”' The letters I. O. mean “Inlet Opens," while I. C. means “Inlet Closed.” The letter S. indicates the sparking point, while U. C. means “Upper Center," which means that the piston is at the top of its stroke, and L. C. means “Lower Center,” which corresponds to the crankshaft position when the piston in the cylinder being timed is at the bottom of its stroke. The numbers in connection with the marks indicate the cylinders in which the functions marked should be taking place.
In addition to the simple elements described it is evident that a gasoline engine must have other parts. The most important of these are the valves, of which there are two to each cylinder. One closes the passage connecting to the gas supply and opens during one stroke of the piston in order to let the explosive gas into the combustion chamber. The other member, or exhaust valve, serves as a cover for the opening through which the burned gases can leave the cylinder after their work is done. The spark plug is a simple device which permits one to produce an electric spark in the cylinder when the piston is at the best point to utilize the pressure which obtains when the compressed gas is fired. The valves of each cylinder open one at a time, the inlet
Fig. 9.—The Packard Twelve Cylinder or Twin Six Unit Power Plant Used on All Late Models of
This Well-Known Car.
valve being lifted from its seat while the cylinder is filling and the exhaust valve is opened when the cylinder is being cleared. They are normally kept seated by means of compression springs and are raised at the proper time by the cams on the camshaft. The engine shown at Fig. 5 is the Dodge and has all valves on one side of the cylinder. That at Fig. 7 is a six-cylinder Buick engine in which the valves are placed directly in the head, open. ing into the center of the combustion chamber instead of at one side. The twelve-cylinder engine shown at Fig. 9 is really two six-cylinder engines mounted on a common crank case; similarly the eight-cylinder shown at Fig. 10 is a twin four.
Cooling Systems.-In order to keep the temperature of an automobile engine within bounds and keep the heat down to a point, where the lubricating oil will not be destroyed or engine parts warped, the cylinders of the engine must be cooled. Two systems of cooling are possible. The simplest involves flanging the cylinders and passing air currents over them. This is seldom used. The accepted method is to pass water around the cylinders through water jackets cast integral with them. If the greater proportion of the heat units derived by burning the explosive mixture could be utilized in doing useful work the efficiency of the gasoline engine would be greater than that of any other form of power producer. There is a great loss of heat from various causes, among which can be cited the reduction of pressure through cooling the motor and the loss of heat through the exhaust valves when the burned gases are expelled from the cylinder. The loss through the water jacket of the average automobile power plant is over 50% of the total fuel efficiency. This means that more than half of the heat units available for power are absorbed and dissipated by the cooling water. Another 16% is lost through the exhaust valve, and but 3313% of the heat units do useful work.
The parts of a forced circulation water cooling system are illustrated at the bottom of Fig. 11. The main parts are a radiator to cool the heated water, a fan to draw air through the radiator and a circulating pump. The water is drawn from the lower header of the radiator by the pump and is forced