Fig. 30. Light Motor Truck Chassis which Follows Typical Pleasure Vehicle Design Except in Size of Parts. The Frame and Running Gear are Heavier and Stronger to Compensate for the Greater Load-Carrying Capacity.

pleasure cars. Figs. 25 to 28 inclusive, depict vehicles which have been designed for special industrial requirements and can be placed in the commercial car class without hesitation, because the bodies fitted and the general design or arrangement of components does not permit their use for any purpose other than that for which they were contrived. All the body forms shown at Fig. 29 are applied to the same type chassis, and it is very common practice to design the running gear and frame so it may be adapted to a wide range of work without changing location of the mechanical parts.

CHAPTER II

How Power is Generated-Two- and Four-Cycle Engine Action-Features of Sleeve Valve Motor-Principal Engine Types Described-One- and TwoCylinder Engines-Advantages of Four- and Six-Cylinder Forms-Power Plant Location.

IT has been previously stated that the gasoline automobile may be divided into groups and that these various assemblies all have their important work to do and that each depend, to some extent, upon the correct action of the others to insure a smooth working motor car. The most important, and the least understood, element is the power plant, and it is important that the prospective motorist familiarizes himself with the principles of gasoline engine operation. in order to easily locate troubles and derangements which interfere with correct action. If the operator is familiar with the basic principles of internal combustion engine action it will not be difficult to apply this knowledge to all forms of gasoline motors used as automobile power plants.

Forms of Engines Commonly Used.-If one raises the hood at the front of a motor car, one will find a complete engine assembly very much the same as that depicted at Fig. 31, which outlines a conventional engine with the various auxiliary parts lettered so that one can obtain an idea of their location relative to each other.

Of the external parts shown the carburetor is employed to mix the gasoline used as fuel with a certain amount of air in order to form a gas that can be ignited in the engine cylinders. This explosive mixture is supplied to the cylinders by a conductor known as the inlet pipe. The spark plugs and magneto form part of the ignition outfit. The engine shown is a four-cylinder form and operates on the four-cycle principle. Various forms of engines have been applied to automobile propulsion, and of the large number of different types the majority operate on the four-stroke principle, though the twostroke types are simpler. In the latter there is an explosion in each

cylinder every turn of the crank shaft, while the other method provides but one power impulse per cylinder every two turns of the revolving elements. Though the four-stroke motor is more complicated in construction than the other it is the easiest to understand. All internal combustion motors, usually termed "gasoline engines" because of the use of this liquid fuel, are forms of heat motors owing to the

Fig. 31.-Typical Motor-Car Power Plant, Showing External Appearance and Location of Important Auxiliary Mechanisms.

energy being produced by the rapid burning, or combustion, of a gas which expands after it is exploded and produces pressure that is transformed into mechanical power by simple mechanism. In defining the principles of four-cycle motor action, one can explain the matter very clearly by comparing the effect produced by exploding gasoline gas to that which obtains when one explodes gunpowder in a gun.