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Fig. 57.-Bottom View of Four-Cylinder Motor Showing Five-Bearing Crank Shaft with Flywheel and

Timing Gear Attached.

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Exhaust manifolds should offer a free passage to the escaping gas and should be large enough in bore so that there will be no friction between the gas stream and the manifold wall.

Q. How is the engine base attached to vehicle frame?

A. The common method of construction is to cast arms integrally with the engine bed which extend to the main frame sides or rest on an inner frame or sub-frame member that is in turn supported by the main frame.

Q. What is the three point support”?

A. If the power plant is supported by three points placed in relation to each other so that the two on the same line form the base of a triangle while the third forms the apex, the engine is said to have a three point support. The advantages of this construction may be readily understood if one compares the action of a three legged stool and one having four legs on uneven ground. The stool with the three point support is not so much affected by irregularities in the surface on which it rests as is the four legged member. A power plant supported on three points is not affected by frame distortion or springing out of alinement as much as a four point support power plant.

Q. What is "four point support”?

A. When a power plant is held in place in the frame by means of four arms so that the point of support forms a rectangular figure, the engine is said to have four point support. The four point system necessitates the use of a more rigid frame than does the three point method of suspension.

Q. What is a unit power plant?

A. The unit power plant construction is that where the engine, clutch and gearset are attached together so these three members may be said to be supported by the same common carrier or case. A unit power plant with the three point support is commonly used in motor car construction.

Q. What are the advantages of the unit power plant?

A. One of the methods of installing the motor and gearset of an automobile is to attach these to a frame as separate members and

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interpose some form of flexible coupling between the clutch shaft and the gear box to compensate for any disalinement of the two members due to frame distortion on rough roads. With a unit power plant, crankshaft, clutch and transmission shafts are held in the absolute alinement present when first assembled, and no amount of frame deflection can throw the three members out of the correctly alined position that insures maximum efficiency and minimum depreciation. (See Frontispiece.)

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Fig. 58.-Outlining Arrangements of Parts of Typical Automobile Fuel Supply System.

LESSON FOUR

FUEL FOR AUTOMOBILE MOTORS

Q. What fuels can be used with the automobile power plant?

A. Internal combustion engines will operate satisfactorily on any form of hydrocarbon gas. This means that natural or artificial illuminating gas, alcohol vapor, acetylene, kerosene, benzol and gasoline vapors may be utilized.

Q. What are the disadvantages to the use of illuminating or natural gas as automobile fuel?

A. In order to carry enough gas for a tour or run of any consequence with an automobile it would be necessary to use very large storage tanks that would occupy considerable space that can be used to better advantages for other purposes. The same disadvantages that apply to the electric automobile regarding its operation at points remote from charging station would apply just as well to the gasoline vehicle if compressed gas was employed as fuel.

Q. What are the advantages of liquid fuel?

A. Liquid fuels have the important advantage that a relatively small supply can be carried in a container of small size compared to the total carrying capacity of the vehicle and that they may be readily handled and stored and easily secured at the present day at even the smallest village or hamlet.

Q. How are liquid fuels changed to gas?

A. A small amount of the liquid is sprayed into a charge of air and the mixture of air and liquid becomes a gas by the time the stream of vapor charged air reaches the cylinder interior. The gasifying process is accelerated by the heat of the motor.

Q. What is the general term applied to all liquid fuels ?
A. The liquid fuels commonly used are generally designated as

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