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Fig. 166.-Group of Parts of Cadillac Eight Cylinder V Motor, Showing Construction of Important

Members of Assembly.

down. Care should be taken when using shellac, white or red lead, etc., not to supply so much that the surplus will run into the cylinder, water jacket or gas passages.

Loose Flywheel.-Many mysterious knocks, which are often attributed to worn bearings are due to the flywheel being loose on the shaft. In a number of the earlier forms of cars and in nearly all marine engines the flywheels are held to the shaft by a simple gib key. It often happens that these keys become worn and the wheel is slightly loose on its supporting shaft. When the engine is revolving at high speed a pronounced thump or knock will be produced because of the hammering action of the flywheel upon the loose key. The proper remedy for such a condition is to make a new key that will fit the keyways in flywheel and shaft and drive it tightly in place. In some constructions the flywheel is installed on a taper on the crankshaft and in addition to the key it is held in place by clamp nuts. These nuts sometimes become loose and permit the flywheel to back off the taper enough to produce noise. In practically all modern forms of motor the flywheel is secured to a flange forged integrally with the crankshaft by means of bolts. It may be possible for the bolts to loosen which will permit the flywheel to rock and to pound the holes out oval. This condition is easily remedied by reaming or drilling the worn holes to the next largest standard size and to fit larger bolts to correspond.

Two Cycle Motors.- This form of power plant has received but limited application in automobiles, but the repairman may have occasion to investigate irregular action of some old model car using this type of motor or may be called upon to repair a marine engine of this type. It will be evident that a worn cylinder, piston rings or piston will result in the loss of compression as in any motor and that loose connecting rods or main bearings will produce noisy operation just as in the four-cycle type. In the two-cycle motors there are other conditions to be looked for besides those involving normal depreciation of the mechanism. There are two chambers to keep tight instead of one as in the four-cycle type. In the twocycle form it is not hard to maintain compression in the combustion chamber because there are no valves to leak and the only chance

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Fig. 167.—Packard “Twin Six'' Motor, Latest Power Plant Development.

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Fig. 168.—End Sectional View of Packard “Twin Six'' Motor, Showing

Arrangement of Cylinders.

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.

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