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removable plate, so that the stub-shaft turns therein freely. A similar gear is mounted on the stub-shaft so that it also revolves thereon. A pair of bevel gears between the aforementioned loose gears, are mounted on spindles attached to the journal-bearing plate, which cause the loose gear on the stub-shaft to travel in a direc- tion opposite to the cylindrical shell.

The fork which is connected with the usual clutch-pedal is used in this device for reversing purposes. The fork engages with a grooved chuck which has radially- disposed tongues, designed to engage with suitable radial grooves in the hub of the loose gear. As the grooved chuck turns with the stub-shaft, although free to move to and fro a limited distance, it can be thrown readily into engagement with the gear, and thus be turned by the stub-shaft in a direction opposite to the fly-wheel or engine-shaft.

Several features of interest may be noted in this device. The pump itself is also the motor, thus eliminating at least one half of the elements usually employed. The double pressure used with the pump and motor systems, is avoided, hence less heat is generated. Aside from this, the oil merely flows in and out of the cylinders, and the friction of movement through long and tortuous ducts is avoided, thereby greatly increasing the efficiency of the device.

One of the most important advances, however, is in the provision for taking care of the oil expansion. In hydraulic systems the cases containing the mechanism must be entirely filled with oil, or with the liquid used to provide the transmission. In this invention the pistons are just as effective if the shell is half filled, for the reason that the ports are at the outer ends of the cylinders, and as the shell revolves the oil is thrown outwardly by centrifugal force so that the ports are always sub- merged with oil and are capable of taking a full charge without drawing in air.

Fully half of the cubical contents of the shell may be devoted to air, or a partial vacuum may be formed therein, thus taking care of any undue expansion. It has been found that a large part of the heat de- veloped and maintained in the hydraulic systems was due to the expansive force exerted on the oil itself, so that large chambers were necessary for this purpose. In a system using two gallons of oil, the expansion of the oil has frequently meas- ured over two quarts.

��Popular Science Monthly

��Softening Carbon with Steam in the Automobile Engine

THE greatest enemy to the free running of an automobile is the carbon which collects in the cylinders of the engine. The

���Injecting water in a small spray into a gasoline engine to soften and partly remove the carbon

carbon may be softened and to a certain extent removed by running water through the cylinders with the gasoline. If a small rubber tube D is attached over the air-cock on the manifold A and run into a pail E of water set at about the level of the carburet- er B, the engine, when running, will suck in the water and then discharge it as steam with the exhaust. After the tube has been removed the engine should be run for a few minutes to make sure that no water remains in the carbureter.

If this is done every thousand miles the car will run much easier. A more thorough job may be done by removing the cylinder head and scraping the carbon away. After the steaming the carbon will be found soft so that most of it can be wiped away with a cloth. The rest is easily scraped off. — William H. Leach.

��An Easy Method of Testing Gasoline Engine Compression

AN important factor having material . bearing upon the power output of the automobile engine is the amount of com- pression of the gas in the cylinders prior to ignition. If one cylinder has less compres- sion than the others, the engine will not pull smoothly under load, as the cylinders having the highest compression will have more power. An easy method of testing gas compression is outlined in the accom- panying illustration. An ordinary tire pressure gage either of the dial pattern or the plunger type may be used instead of the

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