Page:Popular Science Monthly Volume 89.djvu/619

 Popular Science Monthly

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��Loading Small Luggage on the

Outside of the Car CONVENIKXT ••carry-ail" may he constructed in the followint; man- ner and attached to any automohile. Obtain two strips of board i-in. thick and 2-in. wide and cut them to the shape of the front and back fenders respectiveh'.

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���The carry-all takes up the space on the running board on the left of the car

Then purchase 20 ft. of blind stop and from that make a frame as indicated by the dotted lines in the illustration. This frame should be covered with black fiber board on the outside.

Drill six H-'m. holes through the frame and then holding the frame up to the proper position on the car, drill corres- ponding holes in the shoulders on the fenders and running boards on the left- hand sidcof the car. This leaves the "side- walk" side of the car free for entrance. The holes are practically invisible when the ■•carry-all" is removed. Six 3 i6-in. stove bolts 2 in. long with split washers complete the device which gives sufficient room to store luggage. Camp equipment for ten people can be carried without loading the inside of the car.

A black oilcloth tucked in over the equipment keeps rain and dust from the contents and takes away the "bag and beiggage" appearance. It requires only five minutes to take off or put on the frame.

Its cost is as follows:

2 curved pieces and blind stop. . S.40

Covering by trunk maker i.oo

6 stove bolts 05

��Total $1.45

It takes about two hours to make it. The entire contrivance can scarcely be noticed at a short distance from the automobile. A large quantity of dutTel can be carried in it where it may be easil\- obtained when wanted.

��How Piston-Ring Defects Have Been Overcome

THE highly successful behavior of the average autoniotjile and motor- boat engine is due in large degree to the present state of development of the piston-ring. The function of the piston- ring is to form a vapor-tight chamber in which gas may explcxie. impounding its freed energy upon the i)iston-head which transmits this energy to the working parts of the engine. It is evident that the piston-rings must be as vapor-tight as it is possible to make them.

The earliest type of piston-ring was round, of the same thickness throughout, and was slotted to allow for expansion and contraction of the engine as it be- came hot or cold. The concentric ring was soon followed by the eccentric ring. The eccentric ring had a slot similar to the concentric type, but it overcame, one of the defects of the older type — an un- equal distribution of friction against the cylinder-wall. This was accomplished by tapering the thickness of the ring to the point at which the slot was cut. In overcoming the defects of the concen- tric ring, however, the eccentric ring acquired disiidvantages almost as unde- sirable. One of these was that the un- equal thickness of parts of the ring caused carbon to collect in the grooves on the piston-head into which the rings fitted. The great disadvantage of both these types of ring was their loss of energy, which resulted in their inefficiency. High compres- sion was i m - possible, as the gas would escape rapidK- into the crank case below the cylinder. This defect, together with the undesirable features of the two types of rings, has been over- come in a new ring that is now in use. Two of the eccentric-type rings are grooved in such a way that they fit each other perfectly. Vapor cannot escape through cither slot because a thin steel wall pre\ents it. Consequently, while the compression is high, the friction is ecjually clistributed and the wear reduced.

���The rings are grooved to fit perfectly

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