« НазадПродовжити »
one could reasonably expect, but there was not the slightest sign of overheating.
It was then clearly evident that the muffler was at fault, so it was taken apart and the interior carefully examined. The design was such that it would have been a very effective silencer even in normal condition, and the fact that cars of that make had a very enviable reputation for silence kept all concerned from suspecting the muffler until nearly everything else had been tried. The principle of action was to break up the gases before they reached the air by passing them through a number of baffle plates placed at intervals in the muffler shell, these being perforated by a graduated series of holes to allow the gas to pass through. The first holes, that is, those nearest the exhaust intake opening communicating with the engine were about 38 inch in diameter, but each succeeding baffle plate had smaller openings but a greater number, so that the available discharge area was practically the same in all the partition plates. In the member nearest the discharge end of the muffler the holes were normally V8 inch in diameter.
The engine was fitted with a constant level splash system that insured copious lubrication and the owner had not spared the oil. The result was that accumulations of soot had filled the small holes so that they were less than half their normal diameter and the back pressure resulting from this reduction of area had caused both the lost power and overheating. The holes were drilled out to a larger size, 316 inch, so they would not be so liable to fill up again, and after the muffler had been thoroughly cleaned so that all soot was removed from the entire series of baffle plate openings, the component was replaced and the trouble ceased. Enlarging the holes produced a little freer discharge and the car was just a trifle more noisy than it had been prior to the time the holes clogged up and caused defective engine action. Enlarging the openings was advisable, however, as they were not so liable to clog up.
LOCATION AND REMEDY OF IGNITION FAULTS
Battery Ignition System Parts—Care and Wiring of Dry Cells-Storage
Battery Defects--Storage Battery Charging and Maintenance—Ignition
THERE has been no part of the automobile that has been changed more often than the ignition system. The first cars had simple battery and coil ignition, then with the introduction of the high tension magneto the systems were usually combined on the same engine in order to secure double ignition systems, either one being independent of the other. Later, as the magneto became refined and improved, a number of makers discarded the battery ignition system and placed their entire reliance on the magneto. With the coming of the demand for electrical motor starting and lighting systems came a revival of the battery ignition method which had been discarded for the high tension magnetc. The main reason for using the magneto in preference to the battery system was that ignition became weaker with the latter after the engine had been run for a time owing to a lessened output of the battery. The magneto which generates electricity by a mechanical process had the advantage because the faster it was driven the more current it delivered.
In the modern automobiles an electrical current generator is provided, run by the engine which is depended on to charge a
storage battery while the motor is running, the current for ignition and lighting being taken from the storage battery instead of directly from the generator which delivers a current of varying output depending upon the engine speed which in turn regulates the rate of generator armature rotation. On many cars therefore, the battery ignition systems are used as the use of the generator keeps the battery charged always to the proper point for securing energetic ignition. The automobile repairman will have cars to repair that will use a wide variety of ignition systems, as many of those fitted with the simple battery and coil are still in use while a very large number are equipped solely with the high tension magneto. Most of the newer cars will use improved battery ignition systems with the high tension magneto eliminated.
Battery Ignition System Parts.—A battery ignition system in its simplest form consists of a current producer, usually a set of dry cells or a storage battery, an induction coil to transform the low tension current to one having sufficient strength to jump the air gap at the spark plug, an igniter member placed in the combustion chamber and a timer or mechanical switch operated by the engine so that the circuit will be closed only when it is desired to have a spark take place in the cylinders. Battery ignition systems may be of two forms, those in which the battery current is stepped up or intensified to enable it to jump an air gap between the points of the spark plug, these being called “high tension” systems and the low tension form in which the battery current is not intensified to a great degree and a spark produced in the cylinder by the action of a mechanical circuit breaker in the combustion chamber. The low tension system is the simplest electrically but the more complex mechanically. The high tension system has the fewest moving parts but numerous electrical devices. At the present time practically all automobiles use high tension ignition systems, but as the repairman may have occasion to overhaul an “old timer" instructions are given for repairing the low tension ignition systems as well as the more popular forms. Low tension ignition methods are still used in marine engines, so a mechanic working on these types as well as automobiles should familiarize himself with the principles of both high and low tension ignition systems. Ignition troubles are usually evidenced by irregular engine action. The motor will not run regularly nor will the explosions follow in even sequence. There may be one cylinder of a multiple cylinder motor that will not function at all, in which case the trouble is purely local, whereas if all the cylinders run irregularly there is some main condition outside of the engine itself that is causing the trouble. As complete instructions are given at the end of this chapter for a systematic search to locate troubles and as these may be readily identified by the symptoms described, it is not necessary to dwell on this point any longer, at the present time. In a battery ignition system the first point to be suspected in event of irregular ignition is lack of capacity in the current producer.
Care and Wiring of Dry Cells.—The simplest form of current producer is the dry cell which is shown in section at Fig. 224, A. A zinc can about 6 inches high and 212 inches in diameter forms the negative element of the dry cell and also serves as a container for the electrolyte and positive element. A carbon rod placed in the center is insulated from contact with the zinc can by a seal of pitch which is a non-conductor of electricity and which also serves to retain the moisture in the cell. This carbon rod does not extend entirely to the bottom of the cup. The exciting fluid or electrolyte is a solution of sal ammoniac which is held against the negative element by blotting paper which is used as a lining for the zinc can. The space between this active lining and the carbon rod is filled with a depolarizing agent, usually black oxide of manganese, which is mixed with powdered gas retort carbon, the whole being saturated with exciting fluid in order to increase the electrical conductivity of the depolarizing mixture and also to keep the blotting paper lining properly moist. The depolarizor is necessary to enable the cell to be used continuously as it gives off oxygen to combine with the electrolyte after it has given up its chlorine to the zinc which leaves hydrogen to combine with the oxygen and form water. It will be observed that a dry cell is very simple in construction and that nothing is apt to occur that will reduce its capacity except diminution in the strength of the electrolyte or eating away of the zinc can by chemical action. The
elements in a dry cell are usually combined in such proportions that about the time the electrolyte is exhausted, the zinc can will also have outlived its usefulness. It is much cheaper to replace dry cells with new ones than to attempt to repair the exhausted ones.
Evaporation of the electrolyte is the main cause of deterioration of dry cells as the internal resistance of the cell increases when
the moisture evaporates. It is said that dry cells will depreciate even when not in use, so it is important for the repairman to buy these only as needed and not to keep a large stock on hand. In order to test the capacity of a dry cell an amperemeter is used as indicated at Fig. 224, B. Amperemeters are made in a variety