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for escape is by worn piston rings. It is imperative, however, that a certain amount of compression be maintained in the crank case of most two-cycle engines because the degree of compression in the crank case determines the rapidity of transfer of explosive gas from the base where it is first received to the combustion chamber where it is exploded. Because of this the main bearings demand more attention than do those of a four-cycle engine because they must be fitted so well that there is no possibility of leakage through them. Similarly the packings between the cylinder and engine base and between the crank case halves must be carefully maintained. In examining the piston and cylinder care must be taken to remove any deposit of carbon from the baffle plate or deflector which is usually cast integral with the piston top, as any sharp point or corner would remain incandescent and would cause either base firing or premature ignition. Base firing is generally prevented by making the charge from the crank case pass through wire gauze in the by-pass passage. This prevents the flame igniting the explosive gas in the engine base because practically all of the heat is abstracted from any heated gas as it passes through the mesh of the screen. These screens sometimes become clogged with oil and reduce the speed of gas flow and consequently diminish the power output of the motor, the remedy is a simple one as it involves only the removal of the clogged screens and cleansing them thoroughly in gasoline before replacing.

The 12 Cylinder V Motor.—The last word in automobile motor construction is the “Twin Six” motor shown at Figs. 167 and 168. This is very much the same in construction as the eight cylinder forms, one marked difference being in the angle between the cylinders which is 60 degrees and in the use of crankpins wide enough so connecting rod big ends of two opposite cylinders may be placed side by side. Except for the multiplicity of parts which involves slight structural changes, the same instructions given for the repair of the simpler four cylinder engines apply to similar components of the eight and twelve cylinder power plants.



Overheating-Systematic Location of Troubles—Deposits in Radiator and

Piping-Cleaning Sand from Water Jacket-Deterioration of Rubber Hose—Pump Forms and Troubles—Methods of Fan Adjustment-Lacing Flat Fan Belts-Utility of Hose Clamps—Restoring Broken Water Pipe -Radiator Repairs—Defects in Carburetion Group—Gravity Feed Sys. tem-Stewart Vacuum Feed-Air Pressure Fuel Feed-Air Pump Construction-Auxiliary Tanks—Exhaust Gas Pressure-Faults in Carburetor Float Chamber—Troubles in Mixing Chamber-How to Test Float Level-Effect of Air Leaks—Typical Carburetor AdjustmentKingston-Schebler-Browne-Overland Schebler-Breeze-Stromberg Holley—Krice—Zenith-Rayfield-Speed Governors—Carburetor Instal. lation—Soldering Metal Floats—Emergency Manifold Repair-Simple Oiling Systems—Typical Engine Oiling Method–The Constant Level Splash System-Forms of Oil Pumps—Where to Look for Trouble in Lubrication Systems—Cleaning Sight Feed Glass—Curing Smoking Motor-Practical Oil Filter-Requirements of Lubricating Oils.

THE automobile power plant includes various auxiliary systems which are essential to motor action, and defects in these groups will materially influence the power output and regularity of running of the engine. Those that are usually grouped together are the cooling, carburetion and lubrication systems, because defects in any one of these may produce exactly the same effect on power plant operation. For instance, if the cooling system is not functioning properly this condition will be evidenced by overheating. engine will run hotter than it should if lubrication is not adequate owing to friction which produces heating just as lack of proper cooling facilities will. If the carburetor supplies too rich mixture the engine will show this condition by running hotter than it should normally.

Systematic Location of Troubles.--- When a motor overheats it is not possible to discover immediately whether the trouble is du

to improper mixture proportions, lack of adequate cooling or some defective conditions in the lubrication systems. If the motor is overheating because the mixture is too rich this can be determined by studying the character of the exhaust gases. If these have a pungent odor which not only assails the nostrils but which causes the eyes to water as well, and if black smoke is issuing from the muffler one may safely ascribe the overheating to a surplus of fuel in the mixture. Overheating is often due to carbon deposits and if these are at fault they may be removed as indicated in the preceding chapter. The only way to find out if excessive amounts of carbon are present in the combustion chamber is to remove a spark plug or valve chamber cap, and judge the amount of carbon present by inspection of the cylinder head interior. After one ascertains that the overheating is not due to poor mixture or to carbon deposits, it is necessary to inspect the various portions of the water cooling system and also the means of lubrication employed. If an engine is overheating because of lack of oil, it will pound much more than if the abnormal rise in temperature is due to failure of the water to circulate properly, or to the mixture being rich. Steam issuing from the radiator is considered a symptom of defective cooling and is stated to be an infallible indication by some authorities. The writer does not agree with this view, as any motor which is cooled properly when operating under normal conditions will often cause the water in the radiator to boil if the mixture is rich or if lubrication is poor. This does not necessarily indicate defects in the cooling system, but merely shows that the radiation is not energetic enough to absorb excessive or abnormal rise in temperature, due to some cause other than a defect in cooling.

The easiest thing to look for when one's sense of smell indicates that the irouble is not too rich a mixture is some defective condition in the water cooling system. There are two common methods of cooling in general use as outlined at Fig. 169. That shown at A is the simplest, because the water circulates by a natural principle that heated water will rise because it is lighter than cool water. The system shown is used on Overland cars and is the simplest possible method of cooling when liquids are employed for that

purpose. The heated water rising from the cylinders AAAA passes through the cast manifold B, to the top of the radiator D. After it flows through the radiator and becomes cool it returns to the cylinder jacket through the water manifold attached to the bottom of the jacket. The flow of water is indicated by the heavy black arrows, while the draught of cooling air passing through the

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Fig. 169.—Methods of Cooling Automobile Engines Outlined. A.-The

Overland Thermo-Syphon System. B.—Water Circulation by Water

radiator is shown by lighter arrows. In order to assure passage of air currents through the radiator when the car is standing still with the engine running, a power-driven suction fan is placed behind the radiator to draw the air through the interstices between the radiator tubes. With a simple thermo-syphon system the only thing that will interfere with proper circulation of the water is sediment in the water jacket or manifold, defective rubber hose, interruption of fan drive, and constriction of radiator passages. In the system of cooling shown at Figs. 169, B, and 170, a pump is depended on to promote circulation of the water, and in addition to the defects previously enumerated, poor circulation will result if the water pump or its driving means are at fault. The complete cooling system of the Packard four cylinder car is shown at Fig. 171, with all important parts clearly outlined. It will be noticed that whether the thermo-syphon or pump circulation system is used that a cooling fan driven from the engine is considered necessary.

Overland Model 82 Cooling System.—The cooling system (Fig. 170) of the Overland Model 82 is pump actuated. The pump is located on the left hand side of the motor and driven by the magneto shaft, pumping the water from the lower part of the radiator through and around the water areas of all cylinders, as shown in illustration, into the top of the radiator. It is cooled in its downward passage through the radiator and recirculated by the pump. The rapidity of circulation of water is governed by the speed of the motor. The cooling system is therefore positive and absolutely reliable in its action.

The water pump (Fig. 174) is lubricated by means of a compression grease cup. The pump shaft is drilled in the center so that the grease from the one cup supplies both pump bearings. This cup should be given a turn or two every four or five hundred miles. The pump is provided with a drain cock, which should be opened about once a week to let all water and accumulated dirt run out. This drain cock may be used in conjunction with the drain cock on the water pump inlet elbow to drain the water from the cylinders when the car is to be stored in cold weather. The water pump is packed with asbestos and heavily graphited. The glands are countersunk, making the packing conical in shape

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