Page:Popular Science Monthly Volume 91.djvu/793

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Popular Science Monthly

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��more accurate and expensive special pres- sure gage. The tire gages will register correctly in most cases, or at least will show closely the amount of pressure so that it may be compared in the different cylinders.

An adapter fitting is necessary for use with a tire gage, and may be made without difficulty from cast-off parts found in any garage. A discarded spark-plug body forms the main portion of the adapter as shown at A. The inner tube valve-stem is provided with a thread along its entire length for the check-nut used to keep it in place on the tube. A special washer of brass is filed out to fit the seat in the spark- plug body, against which the porcelain is clamped and the valve threaded into place. Of course, if the washer at the bottom of the valve-stem that fits inside the inner tube is large enough, this may be used. Other- wise, the valve-stem should be cut off and screwed into the special seat washer.

The parts are assembled as shown at A and held together by pouring molten lead or babbit around the valve-stem. When the filling material cools, a tight joint is assured because the metal fills the threads in the spark-plug body and valve-stem. To use, the adapter-fitting is screwed into the spark-plug hole as shown at B. The engine may be cranked by the self-starter or turned by hand and the tire gage will show

���Cylinder

A tire gage fitted in a discarded spark plug body to test the compression of a cylinder

the compression in pounds per square inch existing in the cylinder interior if it is held in such a way as to depress the valve inside. A comparison may be made be- tween cylinders by testing each in turn.

If the compression is weak, there is an opportunity for gas leakage somewhere, usually around the piston rings or through the valves. The average compression in a gasoline engine when cold is 75 lb. Some

��engines have 1 less, others more. Compres- sion is determined by the volume of the engine combustion chamber as compared with the total cylinder contents. High compression engines are more apt to knock when carbonized than the low pressure engines. — Victor W. Page.

��Preventing Hinge Rods from Loosen- ing on an Automobile Hood

ON most low priced cars there is no pro- vision made to hold the hood hinge rods in position, and they invariably be-

��Rjveted cap

��Thread

���A round nut turned on the end of the hinge rod keeps an automobile hood from rattling

come loose, due to the vibration. The illustration shows a method of eliminating this trouble. It is only necessary to pro- vide two end caps for the rods, one of which is fastened permanently while the other is free to be removed by using threads. It is also necessary to remove a portion of the hood to provide suitable clearance for the caps. The rods in their new form are held securely in position. — Adolph Klein.

��The Proper Camber for the Front Automobile Wheels

THERE is no specific standard for the camber or canting of front wheels outward at the top, but it is done on most of the cars, to make it easier to steer and turn the curves than would be possible if the wheels were perpendicular. This cam- ber of the front wheels of different cars varies from H in. to \ X A in. between inside felloe measurements. If the Avheels stand too far outward at the top, there is apt to be some binding effect at the axles, and the tires will not roll freely.

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