While troubles existing in the ignition or carburction groups are usually denoted by imperfect operation of the motor, such as lost power and misfiring, derangements of the lubrication or cooling systems are usually evident by overheating, diminution in engine capacity, or noisy operation. Overheating may be caused by poor carburction as much as by defective cooling or insufficient oiling. When the oiling group is not functioning as it should, the friction between the motor parts produces heat. If the cooling system is in proper condition, as will be evidenced by the condition of the water in the radiator, and the carburetion group appears to be in good condition, the overheating is probably caused by some defect in the oiling system

The conditions that most commonly result in poor lubrication as outlined at big. 109 are: Insufficient oil in the engine crank case or sump, broken or clogged oil pipes, filter screen filled with lint or dirt, broken oil pump, or defective oil pump drive. 1 he supply of oil may be reduced by a defective inlet or discharge check valve at the mechanical oiler, or worn pumps. A clogged oil passage or pipe leading to an important bearing point will cause trouble because the oil cannot get between the working surfaces. When simple compression pressure feed lubricators are employed, the check valves may be defective or the container may leak. Either of these conditions will prevent the accumulation or pressure on the surface of the oil, and the feed will not be positive. The sight-feed glasses may fill with oil because the pipes leading from them to the engine are full, or because the conductor is clogged with oil wax. i his gives sufficient warning, however, and the oil pipe may be easily cleared by removing it and blowing it out with air or steam under pressure. It is well to remember that much ot the trouble caused by defective oiling may be prevented by using only the best grades of lubricant, and even if all parts of the oil system are working properly, oils of poor quality will cause friction and overheating.

Cooling systems are very simple, and are not liable to give trouble as a rule, if the radiator is kept full of clean water, and the circulation is not impeded. When overheating is due to defective cooling, the most common troubles are those that impede water circulation as shown in chart, Fig. 110. It the radiator is clogged or the piping or water jackets filled with rust or sediment, the speed of water circulation will be slow, which will also be the case if the water pump or its driving means fail. Some cooling systems are so closely proportioned to the actual requirements’ that the stoppage of a cooling fan will be enough to cause the engine to overheat. Any scale or sediment in the water jackets or in the piping or radiator passages will reduce the heat conductivity of the metal exposed to the air, and the water will not be cooled as quickly as though the scale was not present. The rubber hose often used in making the flexible connection demanded between the radiator and water manifolds of the engine, may deteriorate inside and particles of rubber hang down that will reduce the area of the passage. The grease from the grease cups mounted on the pump shaft bearings to lubricate that member, often finds its way into the water system and rots the inner walls of the rubber hose, this resulting in strips of the partly decomposed rubber lining hanging down and restricting the passage. The cooling system is prone to overheat after antifreezing solutions, of which calcium chloride forms a part, have been used. This is due to the formation of crystals of salt in the radiator passages or water jackets, and these crystals can only be dissolved by suitable chemical means, or removed by scraping when the construction permits.

Overheating is often caused by some condition in the fuel system that produces too rich mixture. Excess gasoline may be supplied if any of the following conditions are present: Bore of spray nozzle or standpipe too large, auxiliary air-valve spring too tight, gasoline level too high, loose regulating valve, fuel-soaked cork float, punctured sheet metal float, dirt under float control shut-off valve, or insufficient air supply because of a clogged air screen. If pressure feed is utilized there may be too much gas pressure in the tank, or the float control mechanism operating the shut-off in either the auxiliary tank on the dash or the float bowl of the carburetor may not act quickly enough.

Fig. 109.—Forms of Oiling Systems that Have Been Used on Motor-Driven Fire Apparatus Power Plants, and Troubles that May Result in Imperfect Lubrication. An Engine is Usually Fitted With But One of the Oiling Methods Shown.Fig. 110.—Conventional Water Cooling System, Showing Parts and Where Trouble May Be Looked for if Engine Overheats.

Considering first the member of the transmission system that will affect the efficiency of the entire assembly when deranged, it will be well to discuss the troubles common to the various types of clutches. The defective conditions that most often materialize are too sudden engagement which causes “grabbing,” failure to engage properly, slipping under load, and poor release. Clutches utilizing a leather facing will cause trouble after a time because of natural wear or some defect of the friction facing. The leather may be charred by heat caused by slipping, or it may have become packed down hard and have lost most of its resiliency. The clutch spring may be weakened or broken: this will cause the clutch to slip even if the leather facing of the cone is in good condition. The two troubles usually met with by the motorist are harsh action, as one extreme condition, and loss of power through slippage as the other.

When the cone clutch, such as shown at the top of Fig. Ill, engages too suddenly it is generally caused by the surface of the leather lining becoming hard and not having sufficient resiliency to yield to some extent when first brought into frictional contact. To insure gradual clutch application, the facing should be soft and elastic. If the leather is not burned or worn unduly it may often be softened by rubbing it with neatsfoot oil. Kerosene oil is often enough to keep the clutch leather pliable and it possesses so little lubricating value that the clutch members are not liable to slip because of a reduced coefficient of friction such as is often caused by the application of more viscous lubricants. Kerosene has other advantages, among which may be mentioned quick penetration of the leather and not collecting grit or gumming.

When a cone clutch slips it is usually due to a coating of oil on the frictional material that decreases the value of the coefficient of friction to such a point that the pressure of the clutch spring is not enough to maintain sufficient frictional contact between the male and female members to insure driving. The remedy for this condition is to absorb the surplus oil by rubbing a small quantity of Fuller’s earth into the leather surface. When the clutch cone is in place it is not easy to reach the surface of the leather, so the first step would be to disengage or release the clutch and to place enough of the Fuller’s earth on a piece of paper or card so it can be sprinkled into the space left between the male and female members when the former is properly released. Borax is sometimes recommended for the same purpose, and when the earth or borax are not available the carbide dust or lime residue from an acetylenegas generator may be used to advantage. If slipping is caused by weakening of the clutch spring it may be prevented by substituting springs of proper strength or by increasing the degree of compression of the weak springs by some means of adjustment if provided for the purpose, such as the nuts on the spring studs of the clutch at the top of Fig. 111.

Fig. 111.—Forms of Motor Car Clutches Generally Used in Motor-Driven Fire Apparatus. Cone Clutch and Three-Speed Sliding Gear Transmission at Top. Typical Cones, Showing Methods of Fastening Clutch Leather, at A and B. Knox Three-Plate Clutch at Bottom.

Another annoying condition that sometimes obtains when a cone clutch is used is spinning or continued rotation of the male member when clutch spring pressure is released. This may be the result of natural causes, but it is sometimes caused by a defect in the clutch mechanism. If the bearing on which the cone revolves when disengaged seizes because of lack of lubricant, the male member of the clutch will continue to rotate even when spring pressure is released. The ball-thrust bearing employed to resist spring tension may become wedged by a broken ball and this will cause the rotation of the crankshaft to be imparted to the cone member, through the spring, which must turn with the crankshaft instead of remaining stationary, as would be the case if the ball-thrust bearing was functioning properly.

On those cars fitted with multiple-disk clutches, as shown at Fig. 112, the same troubles may be experienced as with other types. If a multiple-disk clutch does not release properly it is because the surface of the plates have become rough and tend to drag. The plates of an all metal multiple-disk clutch should be free from roughness, and the surfaces should always be smooth and clean. Harsh engagement also results by the absence of oil in those types where the disks are designed to run into an oil bath. Spinning or continued rotation of a multiple-disk clutch often results from seizing due to gummed oil, the presence of carbon or burned oil between the plates, and sometimes by a lack of oil between the members. When a multipledisk clutch slips it is generally caused by lack of strength of the clutch springs or distortation of the plates. To secure the best results from a multiple-disk clutch it is imperative that only certain grades of oil be used. If one uses a cheap or inferior lubricant it will gum and carbonize because of the heat present when the plates slip, or it will have such viscosity that it will gum up between the plates. Most authorities recommend a good grade of light or medium cylinder oil in multiple-disk clutches where lubricant is required. In some cases faulty multiple-disk clutch action is due to “brooming,” which is the condition that exists when the sides of the keyways or the edges of the disk become burred over and prevent full contact of the plates.

Faulty clutch action has often been traced to points separate from the clutch mechanism. Some cases of failure of clutch to release have been found due to imperfect relation of interlocking levers and rods or wear in some mechanical parts. If a clutch-shifting collar is worn unduly or the small pins in the rod connecting the clutch pedal with the release mechanism have worn to any extent the pedal may be fully depressed and yet the pressure of the spring depended upon to keep the parts in contact will not be reduced to any extent. Sometimes the emergency brake lever may have an interlocking leverage to release the clutch when it is applied, and when the brake rods are shortened to compensate for wear of the brakes the change in length of the operating rods may throw out the clutch mechanism slightly and cause slipping of the clutch because the spring pressure may be partially relieved.

Fig. 112.—Two Types of Multiple Disc Clutches. All Metal Type With Cork Inserts at Top; All Metal Type Without Inserts Shown Separated to Make Details Clear at the Bottom.

The chief trouble with a planetary transmission, as used in Ford cars, and shown in Fig. 113, is caused by slipping clutch bands. These are provided with adjustments that can be tightened in case of wear, and should grip positively. If either the slow speed or reverse bands are adjusted too tight they will bind on the drums and produce friction, which in turn will decrease the efficiency of the drive. Noisy action of planetary gearing is usually caused by lack of lubrication or excessive wear in the gearing. If the oiling is properly taken care of, this condition will be practically eliminated. Sometimes the high-speed clutch may slip, but most planetary gears are provided with adjustable clutches so any wear may be readily taken up.

When slide-gear transmissions are used, the most common defect is difficulty in shifting gears, and noisy operation. The difficulty met with in gear shifting is usually caused by the edges of the teeth of the shifting members having burred over so that they do not pass readily into spaces between the teeth of the gears they engage with. Another cause of poor shifting is deterioration of the bearings, which may change the center distances of the shafts to a certain degree, and the relation of the gears may be changed relative to each other so they will not slide into mesh as freely as they should. Noisy operation is usually due to a defective condition of lubrication, and if the gears are not worn too much it may be minimized to a large extent by filling the gear case with oil of sufficient consistency to cushion the gear teeth and yet not be so viscous that it will not flow readily to all bearing points. A difficulty in shifting is sometimes due to binding in the control levers or selective rods, and these should always work freely if prompt gear shifting is required. If considerable difficulty is experienced in meshing the gears and the trouble is not found in the gearset, it will be well to examine the clutch to make sure that the driven member attached to the gearset main shaft is fully released when clutch pedal is depressed. Typical sliding gearsets are shown in Fig. 114.

While power transmission by chains is not as common at the present time in fire department car practice as it has been in the past, side chain-drive is often employed on the heavier apparatus. Trouble and rapid chain wear can be traced to faulty shaped sprocket teeth, which may not be of the best form adapted for the chain designed to run over them. As most chains are exposed and run without a covering of any kind, the action of the road dust and gravel is to combine with the grease often rubbed on the outside on the pretext of oiling the chain, and forms an abrasive that will produce rapid wear between chain and sprocket and the various links of which the chain is composed.

Fig. 113.—Ford Planetary Gearset at Top. Positive Clutch Constant Mesh Gear Used in Popular Fire Apparatus at Bottom.

To obtain the best results from chain drive the chains must be maintained in correct adjustment by the radius rods provided for the purpose. If a chain is allowed to run too loose it will “whip” and is liable to climb the teeth of the sprocket. If the chain is adjusted too tight there will be strain on all parts, and it is apt to “snap” when it leaves the sprocket, especially if the teeth are worn hook shape.

A safe rule to remember when adjusting chains is to have it tight enough so that it is not possible to raise it from the first tooth with which it meshes on cither sprocket, even with the aid of a lever such as a large screw driver or tire iron.

Chains must be kept clean and properly oiled. The best method of removing the dirt is to take the chain off the sprockets and let it soak long enough in a large pan containing kerosene so all the dirt and gummed oil is removed thoroughly from all the interior bearing surfaces. It should be gone over thoroughly with a stiff bristle brush until each link wprks freely. The chain is then immersed in a pan of gasoline to remove any small particles of grit that the kerosene may have failed to dissolve. After the gasoline bath it is wiped with a clean cloth until it is dry and clean The proper method of chain lubrication is not generally understood and in many instances it is accomplished by coating the” outside of the chain with a graphitegrease combination that serves no useful purpose, and acts merely as a collecting agent for dust and grit. The correct method of chain oiling is by immersing the cleaned chain in a molten mixture of tallow or mineral grease and graphite. The entire chain is immersed in this mixture, which is kept hot so it will penetrate all the minute interstices of the chain links and produce a thin coating of lubricant at all the working surfaces. The chain is removed from the bath of lubricant and while still hot all surplus oil is wiped off until the outside of the chain is dry and clean. This method insures proper lubrication of the many small joints usually neglected. and should be done every thousand miles.

Fig. 114.—Two Representative Forms of Four-Speed Sliding Gearsets. At Top, With Direct Drive on Fourth Speed. Below, Type With Geared-Up Fourth Speed.

But little trouble is experienced with shaftdriving systems because the driving gearing and universal joints are so well enclosed on modern axles The bevel-driving gears are packed in lubricant as a rule, and but little wear is noted, even after several seasons of use. An important point to observe with all forms of axles is to make sure that the antifriction hearings are kept properly cleaned and oiled. The oil should contain no acid and should be of the best quality. Care should be taken in washing the car so that water will be prevented from entering the bearing points. If the bevel gears of the real axle grind it ts due to improper adjustment or excessive wear between the teeth. Grinding sounds usually result from meshing the gears too deeply, while loose adjustment is manifested by rattling.




Part 20, Concluded.

In taking care of a storage battery, there four points which are of the first importance. First, the battery must be charged properly. Second, the battery must not be over-discharged. Third, short circuits between the plates or from sediment under them, must be prevented. Fourth, the plates must be kept covered with electrolyte and only water of the proper purity used for replacing evaporation. In the event of electrical trouble, which may be ascribed to weak source of current, first test the battery, using a low reading voltmeter. Small pocket voltmeters can be purchased for a few dollars and will be found a great convenience. Cells may be tested individually and as a battery. The proper time to take a reading of a storage battery is immediately upon stopping or while the engine is running, if battery ignition is used. A more definite determination can be made than after the battery has been idle for a few hours and has recuperated more or less. A single cell should register more than two volts when fully charged and the approximate energy of a three-cell battery should be about 6,5 to 7 volts. If the voltage is below this the batteries should be recharged and the specific gravity of the electrolyte brought up to the required point. If the liquid is very low in the cell new electrolyte should he added. To make this fluid add about one part of chemically pure sulphuric acid to about four parts of distilled water, and add more water or acid to obtain the required specific gravity, which is determined by a hydrometer. According to some authorities the hydrometer test should show the specific gravity of the electrolyte ns about 1.208 or 25 degrees Baume when first prepared for introduction in the cell, and about 1 106 or 54 degrees Baume when the cell is charged.

Fig. 102—Sectional View of Storage Battery at A Shows Relation of Principal Parts. B— How Storage Battery is Charged from Di rect Current Lighting Mains. C—Outlining Use of Electrolytic Rectifier.

Either voltage or gravity readings alone could be used, but as both have advantages in certain cases, and disadvantages in others, it is advisable to use each for the purpose for which it is best fitted, the one serving as a check on the other A voltage reading has the great disadvantage age in in that that it it is is dependent dependent upon the rate of current flowing. Open circuit readings are of no value, as a cell reads almost the same discharged as it does charged. On the other hand, a voltmeter is a very easy instrument to read and may be located wherever desirable. Specific gravity readings are almost independent of the current flowing, but the hydrometer is difficult to read, not very sentitive and the readings must be taken directly at the cells.

C’opvilght, l9iC~ by Victor W. Page.

Great care should be used in charging and the charging rates given by the various manufacturers should be followed whenever possible. It is essential that the positive wire carrying the charging current be connected with the positive plates of the battery. The positive pole of a cell is usually indicated by a plus sign or by the letter “P”. In case of doubt always ascertain the proper polarity of the terminals before charging. This is done by immersing the ends of the charging wires in acidulated water, about an inch apart. The one around which the more bubbles collect is the negative, and should be connected with negative pole of the battery. A battery always should be charged, if possible, at a low charging rate, because it will mal overheat temperature’is if energized between too rapidly. 70 and 90 The degrees norFahrenheit. enheit. When the battery is fully charged the solution assumes a milky white appearance and bubbles of gas are seen rising to the surface of the electrolyte. All foreign matter should be kept out of the batteries as any metallic substance finding its way into the cell or between the terminals will short circuit the cell and perhaps ruin it before its presence is known. The terminals, the outside of the cell and all connections should be kept free from acid or moisture. A neglect of these essentials means corrosion and loss of capacity by leakage. There is one point in connection with the charge which should be especially emphasized, namely, that the final voltage corresponding to a full charge is not a fixed figure, but varies widely, depending upon the charging rate, the temperature, the strength of the electrolyte and age of the battery. For this reason, charging to a fixed voltage is unreliable and likely to result disastrously. The charge should be continued until the voltage or gravity cease rising, no matter what actual figures are reached. Old cells at high temperature may not go above 2.4 voltage per cell, whereas if very cold, they have been known to run up to three volts.

Fig. 102—Sectional Views Outlining Construction of Various Spark Plug Types.

The points to be especially emphasized in connection with the charge ’are: First, on regular charges keep the rates as low as practical and cut off the current promptly. It is preferable to cut off a little too soon rather than to run too long where there is any question. Second, overcharges must be given at stated intervals and continued to a complete maximum. They should be cut off at the proper point, but when in doubt it is safer to run too long, rather than to cut off too soon. Third, do not limit the charge by fixed voltage. Fourth, keep the temperature within safe limits. Fifth, keep naked flames away from cells while charging as the gas given off is inflammable. Always see that gas vents are clear before charging.

By far the simplest method of charging storage batteries is by interposing a lamp bank resistance instead of the rheostat. These are easily made by any garage mechanic and are very satisfactory for charging ignition or lighting batteries. Standard carbon lamps of the voltage of the circuit shown should be used and the amperes needed for charging can be controlled by varying the candle power and the number of lamps used. If the lamps are to operate on 110 volt circuit, a 16 candle power carbon filament lamp will permit onehalf ampere to pass; a 32 candle power will allow 1 ampere to pass. If it is desired, therefore, to pass three amperes through the battery, one could use 3-32 candle power lamps or 6-16 candle power lamps. If the lamps are to burn on 220 volts it should be remembered that when the voltage is doubled the amperage is cut in half, therefore the 32 candle power, 220 volt carbon filament bulbs will only pass half an ampere.

The method of wiring is very simple, as may be readily ascertained by referring to Fig. 102B. The line wires are attached to a fuse block and then to a double knife switch. The switch and fuse block are usually mounted on a panel of insulating material such as slate or marble. One of the wires, the positive of the circuit, runs from the switch directly to the positive terminal of the storage battery. The negative wire from the switch passes to the lamp bank resistance. The lamps are placed in parallel connection w’ith respect to each other but in series connection in respect to the battery. When coupled in this manner the current must overcome the continued resistance of the storage battery which is very low and that of the lamps. This prevents the battery being charged with current of too high voltage.

Fig. 104—Methods of Testing and Adjusting Spark Plugs.

When only alternating current is available, the chemical or electrolytic rectifier shown at C, Fig. 102, should be used or some other form, either a mercury bulb or vibrator type. These should only be purchased upon the advice of a competent electrician, familiar with local conditions. The rectifiers change an alternating current to a uni-direction flow, suitable for charging storage batteries.

The part of the ignition system that is. apt to give the most trouble, and for the most part through no fault of its own, is the spark plug which is placed in the combustion chamber in order to permit a spark to take place between the electrodes whenever it is necessary to explode a charge of gas. Spark plugs are made in infinite variety, some representative simple forms being shown at Fig. 103. Those in section at A, B, and C, utilize a porcelain insulator through which a central rod or electrode, passes. This terminates at the top in a threaded member, to which the thumb nut is screwed. In most plugs using porcelain insulators a cap is cemented to the top of the porcelain in order to form a seating for the thumb nuts. The form outlined at A is the type of plug most generally used, as it is a simple and effective design. It is easier to clean the points or the interior of the body than in the form shown at B, which has a closed end and which must be dismembered in order to remove the sooty deposit from the insulator serface. The type of plug at C has a very fine wire imbedded in the lower portion of the porcelain which is in connection with a conductor of heavier material used to transmit the current from the terminal nuts to the fine wire. The theory of action of a plug of this nature is that the fine wire is not so apt to be short circuited by soot as the projecting electrode forms are, and that the spark tends to clear away material that might short circuit the current by burning it.

The plugs shown at D and E have mica insulators instead of porcelain. When mica is used a sheet of that material is wrapped around the central electrode several times, after which a series of mica washers are clamped tigthly together and turned down to form a smooth insulator. The plug at F’ is the only one marketed using glass insulation. Other plug forms made on the same general principles as that of A use lava or steatite as an insulator instead of the porcelain or mica. F’or all around service the porcelain insulator gives the best results, as the mica and lava insulators are apt to become oil soaked and permit the current to short circuit through the insulator and the plug body instead of jumping the air gap.

Spark plug troubles are not hard to locate as they may be readily determined on inspection. If an engine misses fire, i. e., runs irregularly, it is necessary to locate the spark plug at fault in order to remove it for inspection or cleaning. The common method of doing this is to short circuit the spark plug terminal with some metallic portion of the engine by using a wooden handle screw driver, as shown at F’ig. 104-A. Each plug is tried in turn, and when a good one is short circuited the engine will run even slower than before. If a plug is short circuited and the engine does not run any slower or work differently, one may assume that the plug is defective or that the cylinder is not firing for some other reason. A very simple spark plug tester which can be made by any repairman for use on cars employing magneto ignition or high tension battery distributor ignition is shown at F’ig. 104B. This consists of two strips of brass riveted together at one end and fitted into a fibre or hard rubber handle. The brass strips are spread apart so that contact may be made between the plug body and the insulated central terminal of practically any size plug. The common trouble is a deposit of burnt oil’ or carbon around the insulator and between the plug points. This short circuits the current as it provides an easier path for the passage of electricity than the air gap does. If the points are too close together the plug will become short circuited very quickly and ignition is apt to be erratic because the spark does not have sufficient heat to ignite the mixture. If the spark points are too far apart the resistance is apt to be too great for the current to jump the air gap. The porcelain may crack or become broken, in which case the current is apt to short circuit if the break is down in the plug body. If a mica or lava insulator becomes oil soaked, this also will produce, short circuit.

Most plugs are of the easily separable form, as shown at Fig. 103-A, in which case the insulator may be easily removed by unscrewing the packing nuts that keep it seated against the plug body. If the plug is clean when examined the thing to do is to sec that the spark gap is correct. This should be about one-thirty-second inch for magneto ignition or one-sixteenth inch for battery and coil system. Whenever a spark plug is to be put into use, whether it is a new one or old one which has been cleaned, the spark points should always be set so there is a gap of about the thickness of a smooth ten cent piece between them. The method of obtaining a correct spark gap depends entirely upon the type of the plug. In the plug shown at Fig. 104-C, which has a plate at the end, it is necessary to bend over the center stem by using a small screw driver or similar tool as indicated. With a plug of the form shown at D, the center stem is bent the proper distance away from the small hook-shaped wire or electrode which projects from the bottom of the spark plug body. In some plugs it is easier to bend the central stem than the side electrode, as the latter is of hard material whereas in others it is not possible to bend the central electrode and the point attached to the plug body must be bent instead.

Fig. 106—Showing Cohtact Breaker Arrangement of Bosch DU-4 Magneto at A. BMethod of Cleaning Contact Points of Oil Deposits. C—Standard Spark Plug Showing Correct Gap Between Points. D—Contact Breaker and Distributor of Remy Magneto.Fig. 105—View of High-Tension Magneto, With Distributor and Contact Breaker Covers Removed to Show Arrangement of These Important Parts.

It is important when replacing the porcelain insulator after cleaning to make sure that the packing nut is drawn down quite tight in order that the joint will be tight enough to hold the explosion pressure. it is also necessary to screw down the small hexagon lock nut on top of the spark plug porcelain, as if this is left loose the center stem of the plug will be free to turn in the porcelain, especially if the thumb nut or terminal is being tightened. It will be apparent that if the center stem is bent over toward the side electrode in the manner shown at D, that if it is turned a very small part of a circle the size of the gap between the center stem and side electrode will be altered appreciably. If the porcelain is found covered with oil and carbon, when removed, it should be thoroughly cleaned, care being taken not to scratch the glazing on the porcelain surface, as if this glaze, is destroyed it will be possible for the porcelain to absorb oil. The interior of the plug body and the electrodes should also be scraped clean of all carbonaceous matter. If the porcelain is scratched or defaced in any manner it should be replaced with a new one. If the plug is apparently in good condition and yet the cylinder refuses to fire, it may be well to substitute the plug with one known to be in good condition, as rtiere may be some minute short circuit in the porcelain that is not apparent upon inspection.

Plugs using mica insulation arc very deceptive, as in many cases short circuits exist that cannot he detected by the eye in daylight. A good way to test a suspected mica plug is to lay it on top of the cylinder after dark, taking care not to have the insulated terminal in contact with any metal parts except the high tension current lead. The engine is then run on the other cylinders and the inside of the spark plug watched to see if sparks jump between the insulators and the plug body, instead of between the points. If a short circuit exists it will be easily detected by the minute sparks plainly evident in the darkness. It is sometimes possible to test a plug out in daytime by shading it from light In some manner, as with a black felt hat. After the spark points have been set correctly, it is well to double up a piece of emery cloth with the abrasive surface on the outside, as shown at Fig. 104-E and move it back and forth between the plug points a number of times to brighten them up and to insure that there will be no foreign matter present between them that is apt to short circuit the current. An old tooth brush and gasoline are the best tools for cleaning a spark plug without taking it entirely apart as stiff brush bristles will remove any oil or material soluble in gasoline. Acetone is a solvent for carbon, and if that material is not baked on too hard it is possible to remove the deposit without scraping it off.

Fig. 107—Typical Wiring Diagram of Double System Using Low-Tension Transformer Coil Magneto.

The most popular form of magneto, if one can judge by the numbers of manufacturers using it, is the true high tension type with the revolving winding, though the low tension type using transformer coils have also been used to a large extent. In case of trouble with a magneto, the point to be determined, first of all, is whether the fault is with the current generator, if it is a true high tension form or in the plugs, or in the event of a transformer coil being employed, if that member it at fault. In cases where only one cylinder is firing irregularly the fault is very likely to be with the spark plug in that cylinder. The common troubles of spark plugs and the method of repairing them have been previously described. After the spark plugs have received attention the cables must be tested to make sure that the insulation is not injured in any way or that the metal terminals at the end of the cable do not come in contact with any metal parts of the motor or magneto. If the ignition fails suddenly one can suspect a short circuit in the grounding cable, which is connected to the nut on the magneto contact breaker and which serves for switching the ignition off. This may be easily ascertained by removing the cable from the magneto and seeing if its removal enables the magneto to run correctly. A spark leaping the gap in the safety device indicates a broken wire or one that has become disconnected either from the plug terminals or from the distributor terminal.

If the cables and plugs are in good condition and the engine works irregularly, it is apparent that the trouble is in the magneto, if it is an ignition fault. In event of this, the most important thing to do is to make sure of the proper interruption of the primary current. The spring holding the cover of the contact breaker in place should be moved sideways and the brass cover taken off. It is then important to see if the screw P, Fig. 106, is tight. If this is found to be set up properly the next thing is make sure that the contact breaker points are in contact when the lever CF is away from the cams in the breaker box in the type DU-4 or away from the fibre cam rollers in the type D-4. It is also important that the platinum points are separated by the proper distance, about .5 millimeter, when the lever CF is in contact with the cam. If the points are too far apart they should be brought nearer together by lossening the lock nut on the adjusting screw and screwing it up to lessen the difference, or to screw it back and open the gap if it is not sufficient. The platinum contact points must also be cleaned, any dirt or oil being easily removed, as shown at Fig. 106-B, by gasoline squirted on them from a small hand oil can. In case the contacts are uneven, pitted or blackened they must be smoothed with a jeweler’s fine cut file. After continued use, if the platinum points have worn down, the platinum-pointed screw must be removed. It is also important to make sure that the high tension current collecting brush is in contact with the collector ring, and that the conducting pencil makes proper contact with the brush against which it bears. The interior of the distributor must be clean and free of metallic or carbonaceous matter. The distributing brush must bear postively against the distributor section and the interior of the distributor should be smooth and all contacts clean and bright.

Fig. 108—Diagram Illustrating Method of Timing Magneto for Four-Cylinder Engine Ignition.

Mention has been previously made of making sure that the screw which keeps the contact breaker assembly in proper relation with the armature shaft is tight, which calls for careful attention. If this screw is loose, the contact breaker assembly will not move in proper timed relation with the armature; in fact, it may not move at all, which will prevent the contact point from separating and which will also result in failure of the ignition. If everything appears to be all right about the magneto, the timing should be verified to make sure that the spark is occurring at the right time in the engine cylinders. It is easy to tell if the magneto is producing a spark of proper intensity by uncoupling a spark plug conductor and holding it a sort distance away, not more than one-eighth inch from the terminal and noting if a spark jumps the gap as the engine is turned over rapidly by hand or with the electric starting motor.

Timing Magneto Ignition Systems—An ideal method of magneto placing and one followed by a large number of manufacturers, is shown diagramatically at Fig. 108. In this the device is fitted to a four-cylinder engine and as the armature must be driven at the same speed as the crankshaft it is necessary to use but one extra gear, that being the same size as the engine shaft pinion and driven by the camshaft speed reduction gear. The sketch also illustrates one method of timing the magneto, which is one of the direct hightension type. The position of the various parts is clearly shown. Having fixed the magneto to the engine crankcase, the driving pinion, or one of the members of a flange or Oldham coupling, is put loosely on the tapered end of the armature shaft, and tfie cover to the distributor and the dust cover of the contact breaker are removed to allow one to control the position of the armature. The motor is now turned over by hand so the piston in the first cylinder is at top center, which can be determined either by watching the crankshaft through a suitable opening in the engine base, by reading the marks on the flywheel rim, or by inserting a wire through a compression relief petcock or spark plug hole.

The armature of the magneto is then brought to the position indicated in sketch, which represents the fitting of a magneto that is turning clockwise when viewed from the driving end. The distance between the end of the armature and the pole piece should be between 14 and 17 mm or between .5511 inch and .6692 inch. This represents an advance of about .5 inch on a motor with a five-inch stroke. The armature is uncovered by removing the flat casing cover lying between the horseshoe magnets, this often carrying the safety spark gap and normally serving as a lid. If earlier timing be desired for any special purpose the gap may be widened a trifle, if it be thought the timing is too far advanced, the gap may be lessened. The contact breaker is fully advanced at this time and the contact points are just about to separate. Having placed everything in position as described, tighten the coupling on the taper shaft and ream out for a small taper pin, to insure positive retention of timing.

Editorial note: The concluding installment of this series, to be published in an early number, will consider troubles in the cooling, lubrication and power transmission systems.