engine-bed proper and carries the cylinders and crank shaft. The arms by which the engine is supported on the tractor frame are cast integrally with the upper member. The lower portion of the crank case serves merely as an oil container and cover for the working parts and may be easily removed to permit thorough repairing of the interior mechanism.

A superficial examination of the parts is made possible

FIG. 53.-Crankcase of Russell Three Cylinder Tractor Motor Composed of Two Halves and is Split Longitudinally at Crankshaft Center Line.

by means of readily removable plates at the side of the crank case, though when repairs of a serious nature are made, such as adjusting the connecting rods or main bearings, it is best to remove the lower half of the engine base. A four-cylinder crank case of the barrel type is

shown at Fig. 54. As will be seen this construction calls for the use of end-bearing plates, which carry the front and rear main journals, while the three main bearings inside the crank case are attached to the partitions which separate the lower portion into four compartments. The cylinders are held in place by a series of stud bolts screwed into the top of the case. In order to gain access

FIG. 54.-Crankcase of Holt Tractor Engine, a One Piece Casting With Removable Side Inspection Plates.

to the interior large openings are provided at both sides. of the crank case and are closed by substantial cover plates, such as shown leaning against the engine base when the assembly is completed. The main object in engine-base design is to have the member a substantial one that will keep the crank shaft rigidly in line with the connecting rods and pistons and which will be of such design that the various parts will be accessible for inspection or adjustment without having to dismantle the entire power plant.

CHAPTER V.

MAKING AND EXPLODING THE GAS.

The Liquid Fuels-Gasoline-Kerosene-Alcohol-Elements of Carburetion-Simple Mixing Valves-Float Feed Carburetor Action-Automatic Carburetors-Parts of Carburetors -Typical Gasoline Carburetors-Carburetor for Twocycle Engines-Action of Kerosene Vaporizer-Methods of Exploding Charge-Advantages of Electric IgnitionMethods of Producing Current-Dry and Storage Batteries— Function of Induction Coil-Producing Spark in Cylinders-Mechanical Generator Advantages-Types of Magnetos-Oscillating Armature Forms-Types with Revolving Armature-True High Tension Device-Low Tension Ignition System-Simple Battery Ignition MethodsAction of Magneto Ignition System-Timing the Spark. The Liquid Fuels. The great advance of the internal combustion motor can be attributed more to the discovery of suitable liquid fuels than to any other factor. The first gas engines made utilized ordinary illuminating gas as a fuel, and while this is practical for use with stationary power plants wherever it is available, such as the natural gas fields of the Middle West, or in cities and towns having a central gas producing plant, it is obvious that it could not be very well applied to portable self-propelling power plants used for tractor propulsion. When it was discovered that certain of the liquid fuels belonging to the hydrocarbon class, which includes petroleum and its distillates, benzol and benzene, which are coal tar products, and alcohol, were suitable, the gas engine became widely used as a prime mover.

The liquid fuels have the important advantage that a quantity sufficient for an extended period of engine operation can be easily carried in a container that will not tax the capacity of the engine and that requires but comparatively little space in any out-of-the-way portion of the frame. When used in connection with a simple vaporizing device, which mixes the liquid with sufficient quantities of air to form an inflammable gas, the fuel is automatically supplied to the engine without any attention being demanded from the operator as long as the supply in the tank is sufficient to produce a flow of liquid through the pipe joining the mixing device and fuel container.

Gasoline.—Up-to-date the most important fuel used in connection with gas engines has been one of the distillates of crude petroleum, known generally to the trade as "gasoline." This liquid, which is a clear white very light bodied substance, evaporates very rapidly at ordinary temperatures. This feature made it especially adaptable for use with the early forms of mixing valves because it mixed so readily with air to form an explosive gas. Fifteen years ago there were very few industrial uses for gasoline and it sold for less than five cents a gallon in some cases. During the past decade the demand for it has increased by leaps and bounds, and it now sells for four times as much as it did when the gasoline engine was first introduced.

The specific gravity of gasoline varies from sixty to seventy-six degrees, though very little of the latter is now obtainable except by special arrangement with the oil producing company. It was formerly thought that gasoline any heavier than seventy-six degrees would not work satisfactorily in the cylinders of the gas engine, and while this is true of the early crude and

inefficient vaporizers, modern mixing devices have been evolved which handle gasoline of sixty-two degrees specific gravity and even heavier. The percentage of gasoline produced from crude oil in proportion to the other elements is very small, and as the demand has increased to such proportions, the tendency of the producer has been to make gasoline heavier or of lower

FIG. 55. Graduate A Shows Proportion of Different Products Obtained From Kansas Crude Oil. The Fractional Distillation of Gasoline is Shown in Graduate B. of Making Baumé Test Shown at C.

Method

specific gravity by distilling off some of the heavier oils with it to increase the bulk produced.

If one refers to graduate A shown at Fig. 55, the proportion of gasoline obtained by distillation from