Roger B. Whitman

“ When a battery is exhausted, or nearly so, it will not magnetize the core of the coil sufficiently to induce a current that will give a strong enough spark to ignite the mixture. The length of time that a battery should last, or the mileage that it should give, is learned from experience, and when it is exhausted in less time there is evidence that it has either been short-circuited or that the current has been used too extravagantly. ”

“ IGNITION The charge of explosive mixture in the combustion space is ignited, or set on fire, by an electric spark, and the apparatus for producing and controlling this spark is called the ignition system. It is with this part of the mechanism of an automobile that a novice has the greatest difficulty, for an electric current is usually regarded as being surrounded by an air of mystery. ”

“ To understand the action of the differential, imagine the rear wheels of a car to be jacked up clear of the ground so that they are free to revolve, and the housing to be revolved by hand. As it turns, the driving wheels will turn also, for the resistance to each is the same, and the pinions, being in mesh with both bevel gears, cannot revolve on their studs. If one of the wheels is now held stationary and the housing revolved, the bevel pinions will revolve on their studs, and roll around on the stationary gear ”

“ It is obvious that in order to obtain a current of the greatest strength the conductor by which it flows must present the least possible resistance, and for this reason copper is used almost universally to convey the current from one place to another. A copper wire will carry safely a current that would heat an iron wire of the same size to the melting point. The resistance of a small conductor is much greater than that of a large one, so that the size of a conductor must always be considered in relation to the current that is to be conveyed. ”

“ The defects of two-cylinder vertical engines with either design of crank shaft outweigh any possible advantage of that construction, and the horizontal double-opposed type, in evenly occurring power strokes, mechanical balance, and simplicity, is in almost universal use for cars of low power.
A two-cylinder engine does not require so heavy a fly wheel as a one-cylinder engine in proportion to the power delivered, because there is a power stroke every revolution instead of in alternate revolutions, and the parts must be carried over only one dead stroke instead of three. ”

“ A magneto is a machine that when driven generates an electric current, and is in almost universal use for this system of ignition. In many cars the system is so arranged that the driver has his choice between ignition by battery and coil, as described, and ignition by magneto, but the mechanical production of a current is so reliable that many automobile builders rely on the magneto alone. ”

“ To make a practical application of the laws governing the production of an induced current, a conductor forming a closed circuit is placed in a magnetic field, and the strength of the field caused to change, alternately becoming strong and weak. In magnetos, the magnetic field is due to two or more powerful steel magnets, and the conductor, a length of insulated copper wire, is wound on a soft iron core and revolved between the poles of the magnets [Pg 256] where the field is strongest. The magnets are known as the field of the magneto, and the wire on its core the armature. ”

“ A gasoline engine is similar to a steam engine in that its piston is moved by the pressure exerted by a heated and expanding gas; it is different in that the pressure is produced inside [Pg 4] of the cylinder by the combustion of an inflammable mixture of gasoline vapor, instead of being generated in a boiler away from the cylinder. The heat of the combustion creates great pressure, and as the piston is the only part that can give before it, it is moved from one end of the cylinder to the other, this motion being utilized in the turning of the crank shaft. ”

“ The ignition system is the greatest producer of trouble, and the reason is usually difficult [Pg 180] to locate. Any interference with the flow of the current, or leaks by which it evades passing over the entire circuit, will cause irregular running or the stopping of the engine, and the circuit must be maintained in the best possible condition in order to prevent these as much as possible. The wires should be well insulated, the insulation of the secondary circuit being heavier than that of the primary because of the higher pressure of the current that must be retained. ”

“ The type of engine that will give satisfaction depends on the work that is demanded of it, the care that it will receive, and the knowledge of the operator. A one-cylinder engine, having a minimum of parts, may be successfully managed by a novice, but its vibration, and the fact that it delivers power for only one fourth of the time that it runs, make it unsatisfactory for any but light work. ”

“ A wire of nonmagnetic metal, such as copper, for instance, will not have the slightest attraction for iron filings, but when an electric current is passed through it the filings will act as if the copper were a magnet, clinging to it as long as the current passes, and dropping as soon as the circuit is broken. As a matter of fact, an electric current sets up lines of magnetic force exactly similar to those of a permanent magnet, their number being in proportion to the strength of the current. ”

“ The driving-shaft type has the advantage of the perfect lubrication of the parts, for all may be inclosed and running in oil or grease; the rear axle must be divided, however, which requires it to be heavily braced in order that the weight imposed on it may not bend or spring it out of line. Where a bent dead axle can be straightened by a blacksmith, a similar condition in a live axle requires the services of an expert mechanic; on the other hand, bevel gears make less noise than chains. ”

“ The high compression through which the spark is required to pass presents greater resistance than air at atmospheric pressure, practically in proportion to the pressure, and a current that will produce a spark outside of the cylinder may not have sufficient pressure to give a like result when the engine is running. If the pressure of the compression is four times that of the atmosphere, the current should be able to produce a spark four thirty-seconds, or one eighth, of an inch long outside of the cylinder, and for safety this should be increased four-fold. ”

“ A grounded circuit requires careful insulation of the lead wire, for as it is very likely to come into contact with the metal of the engine, a break in the insulation would permit the current to leak and to return to the generator without doing its work, this condition being called a short circuit. Grounding the circuit saves wire and reduces complication; simplicity is important in automobile work, and a reduction of the parts much to be desired. ”

“ If the engine were to be run at a constant speed, the relative pressures on the gasoline in the float chamber and spray nozzle, and the quantity of gasoline forced out of the spray nozzle, would remain in correct proportion to the volume of air; but as the engine of an automobile is run at greatly varying speeds, the pressure in the mixing chamber is not constant, but varies to correspond. If the piston makes fifty inlet strokes a minute, the reduction of the pressure in the mixing chamber is more gradual than would be the case with the piston making two hundred inlet strokes a minute. ”

“ A lack of lubricating oil, either through the failure of the supply or the clogging of the pipes, will cause the engine to heat and the piston to stick or seize. When the car is new, it is better to supply too much oil than too little, but when the bearings have smoothed down the supply may be reduced. The operation of the engine is the only indication as to whether it is receiving a proper amount of oil, and rather than run the risk of underlubricating the piston rings and cylinder walls, it is better to have enough to produce a faint smoke at the exhaust pipe. ”

“ The power developed by a gasoline engine being greatly dependent on its speed, and there being no reserve by which greater power can be developed in emergencies, it is necessary for an engine of this type to be perfectly adapted to the work that is desired of it. At excessive speeds the piston acquires great momentum, which must be overcome at each end of a stroke by the crank shaft, and while a speed above normal may be attained, it results in the quick destruction of the bearings and the severe straining of the engine. ”

“ It is most inadvisable to take a magneto to pieces without an exact knowledge of its construction. Except for lubricating the bearings, it is best to leave it entirely alone. In setting a magneto, it must be remembered that it is not delivering current continuously, and that when the iron core of the armature is parallel to the poles of the magnets no current is produced. ”

“ When the piston is moving slowly, the mixture may be ignited toward the end of the compression stroke, for there will be sufficient time for complete combustion by the time the stroke is ended; but when moving at high speed, ignition must occur much earlier in the stroke, as otherwise the piston will have completed the compression stroke and begun to move outward on the power stroke before the mixture is entirely burned. The instant at which ignition occurs also depends on the mixture that is used, for its quality and proper combination make a difference in the rapidity with which it burns. ”

“ Even when on the direct drive, the crank shaft makes more revolutions than the rear wheels, in order that the momentum of the moving parts of the engine may be sufficient to keep the car in motion. On shaft-driven cars, the bevel on the driving shaft has fewer teeth than that on the axle, so that it revolves more than once to one revolution of the axle. ”

“ Future development of the internal combustion engine will no doubt eradicate this, to the increase of efficiency and economy.
The charge of inflammable mixture can produce a certain amount of heat, and the more rapidly and completely this heat is obtained, the greater and more sudden will be the rise in pressure. The pressure will be greater when the mixture is contained in a small space than when in a large, and as the combustion space is smallest when the piston is at its inmost point, the greatest pressure will be obtained if combustion is complete at this point. ”

“ Because a gasoline engine must be in operation before it can deliver power, a clutch is provided by means of which it may run free or be so connected that it drives the car, one of its two chief parts being attached to the engine and the other to the transmission. When the two parts are in contact, the transmission is driven, and when separated, the engine and transmission are independent of each other, and may be stationary or in motion. ”

“ Practically all ignition circuits are provided with two sources of current, so that in case of the failure of one the other will be available, and either may be connected into the circuit by means of a switch. The simplest form of switch is a piece of flat spring brass, pivoted at one end so that the other may be swung from side to side to make contact with one or the other of two brass knobs, or switch points. One pole of each generator, usually the negative, is grounded, and the other connected to one of the points. ”

“ The jump-spark or high-tension system of ignition depends on the production of a current at such a pressure that it can jump from one point to another through high resistance, such as is presented by air at ordinary or low temperature, and especially when compressed, the spark occurring as it passes. ”

“ One dry or storage cell does not give a sufficient current to supply the required spark, and several must therefore be used. The most usual method of connecting dry cells, and the only method of connecting storage cells, to form a battery, is to connect the negative pole of the first cell to the positive pole of the second, using a short length of insulated wire of sufficient size, the negative of the second to the positive of the third, and so on, until all of the cells necessary to supply the required current are used. ”

“ A loose connection presents resistance to the flow of current, and the current will flow irregularly, as the vibrations bring the terminals together or separate them. A wire broken at a terminal is easily seen, but when a break occurs inside of the insulation, it is more difficult to detect. When a broken wire is suspected, its circuit may be located by testing, and new wires laid, one length at a time, until the faulty one is replaced. It is poor economy to use cheap wire, for the best is none too good for the hard use to which it is put. ”