lating to wiring and also the character of the spark plugs employed. The conductor should be of good quality, have ample insulation and be well protected from accumulations of oil which would tend to decompose rubber insulation. It is customary to protect the wiring by running it through the conduits of fiber or metal tubing lined with

Fig. 207.-Method of Applying Bosch Dual Ignition System to Conventional Four-Cylinder Power Plant.

insulating material. Multiple strand cables should be used for both primary and secondary wiring and the insulation should be of rubber at least inch thick.

The spark plugs commonly used for battery and coil ignition cannot always be employed when a magneto is fitted. The current produced by the mechanical generator has a greater amperage and more heat value than that obtained from transformer coils excited by battery current. The greater heat may burn or fuse the slender points used on some battery plugs and heavier electrodes are needed to resist the heating effect of the more intense arc. While the current has greater amperage it is not of as high potential or voltage as that commonly produced by the secondary winding of an induction coil, and it cannot. overcome as much of a gap. Manufacturers of magneto plugs usually set the spark points about of an inch apart. The most efficient

magneto plug has a plurality of points so that when the distance between one set becomes too great the spark will take place between one of the other pairs of electrodes which are not separated by so great

an air space.

Expert motorists championed the cause of mechanical generators of electricity some time ago, but it is only within the past year or two that the public demand for these devices impelled manufacturers of motor cars to supply them as regular equipment on their cars.

CHAPTER VII

Reason for Lubrication of Mechanism-Lubricants and their DerivationMethods of Supplying Oil-Typical Lubrication Systems Outlined- -Theory and Functions of Cooling Systems-Water-Cooling Methods Explained-Elements of Simple Circulating System-Forced Circulation and Apparatus -Thermosyphon-Cooling Methods-Air-Cooling Systems.

THE importance of minimizing friction at the various bearing surfaces of machines to secure mechanical efficiency is fully recognized by all mechanics, and proper lubricity of all parts of the mechanism is a very essential factor upon which the durability and successful operation of the motor car power plant depends. All of the moving members of the engine which are in contact with other portions, whether the motion is continuous or intermittent, of high or low velocity or of rectilinear or continued rotary nature, should be provided with an adequate supply of oil. No other assemblage of mechanism is operated under conditions which are so much to its disadvantage as the motor car, and the tendency is toward a simplification of oiling methods so that the supply will be ample and automatically applied to the points needing it.

In all machinery in motion the members which are in contact have a tendency to stick to each other and the very minute projections which exist on even the smoothest of surfaces would have a tendency to cling or adhere to each other if the surfaces were not kept apart by some elastic and unctuous substance. This will flow or spread out over the surfaces and smooth out the inequalities existing which tend to produce heat and retard motion of the pieces relative to each other.

A general impression which obtains is that well machined surfaces are smooth and while they are apparently free from roughness and no projections are visible to the naked eye, any smooth bearing surface, even if very carefully ground, will have a rough appearance if examined with a magnifying glass. An exaggerated condition to

illustrate this point is shown at Fig. 208. The amount of friction will vary in proportion to the pressure on the surfaces in contact and will augment as the loads increase, the rougher surfaces will have more friction than smoother ones and soft bodies will produce more friction than hard substances.

Friction is always present in any mechanism as a resisting force that tends to retard motion and bring all moving parts to a state of rest. The absorption of power by friction may be gauged by the amount of heat which exists at the bearing points. Friction of solids may be divided into two classes, sliding friction, such as exists between the piston and cylinder, or the bearings of a gas engine and rolling friction, which is that present when the load is supported by ball or roller bearings or that which exists between the tires or the driving wheels and the road. Engineers endeavor to keep friction

losses as low as possible and much care is taken in all modern automobiles to provide adequate methods of lubrication, or anti-friction bearings at all points where considerable friction exists.

Theory of Lubrication. The reason a lubricant is supplied to bearing points will be casily understood if one considers that these elastic substances flow between the close fitting surfaces, and by filling up the minute depressions in the surfaces and covering the high spots act as a cushion which absorbs the heat generated and takes the wear instead of the metallic bearing surface. The closer the parts fit together the more fluid the lubricant must be to pass between their surfaces and at the same time it must possess sufficient body so that it will not be entirely forced out by the pressure existing between the parts.

Oils should have good adhesive, as well as cohesive, qualities. The former are necessary so that the oil film will cling well to the surfaces of the bearings; the latter, so the oil particles will cling together and resist the tendency to separation which exists all the time the bearings are in operation. When used for gas-engine lubrication the oil should be capable of withstanding considerable heat in order that it will not be vaporized by the hot portions of the cylinder. It should have sufficient cold test so that it will remain fluid and flow readily at low temperature. Lubricants should be free from acid, or alkalis, which tend to produce a chemical action with metals and result in corrosion of the parts to which they are applied. It is imperative that the oil be exactly the proper quality and nature for the purpose intended and that it be applied in a positive manner. The requirements may be briefly summarized as follows:

First-It must have sufficient body to prevent seizing of the parts to which it is applied and between which it is depended upon to maintain an elastic film, and yet it must not have too much viscosity in order to minimize the internal or fluid friction which exists between the particles of the lubricant itself.

Second-The lubricant must not coagulate or gum, must not injure the parts to which it is applied, either by chemical action or by producing injurious deposits, and it should not evaporate readily.

Third-The character of the work will demand that the oil should not vaporize when heated or thicken to such a point that it will not flow readily when cold.