Latest Improvements in the Franklin Air-Cooled Engine From the time when it made its first appearance before the American public, the Franklin engine has always been note d for its light weight, powerfulness, and especially for its air-cool-i n g feature. When this little engine was fi r s t brought out over five year s ago, it consisted 0 f four cylinders of 314- inches bore and s t r o k e, and rate d at 7 horse - power. The next year, by refinements in construction, the horsepower was raised to 10; and subsc-q u en tl y, by adding an auxiliary exhaust, and thus disposing of the burnt gases faster and more effectively than is done in any other type of engine, the horse-power was raised to 12. For 1908, by the addition of a cylinder with a dome head and having a single concentric valve, the horse-power of this same sized engine has increased to 16, or, in other words, it is now over 100 per cent greater than it was at the start five years ago. Thus, in a half decade, Mr. John Wilkinson, the inventor of this engine and car, has not only been able to make a success of a type of engine which the French gave up in disgust, but he has also succeeded in obtaining results in the line of durability and economy which has not been duplicated abroad by the French or by any other nation. Aside from the fact that it is placed in a cylinder head which is shaped correctly for the highest efficiency, the new concentric valve is interesting in itself as regards its construction and method if operation. Something of this sort was tried several years ago upon the Lanchester air-cooled engine made in England, but the valve used in that engine was constructed differently, and was subsequently abandoned. The new Franklin arrangement consists of a valve within a valve. The outer, or exhaust valve, is merely a shell having a long hollow stem through which passes the stem of the inlet valve, 2. This latter valve seats against the inner surface of the shell, that is, against the part, 1, which forms the seat of the exhaust valve. Both valve stems are provided with washers and springs, as can readily be seen from a glance at (Continued on page 346.).
This article was originally published with the title "Engines" in Scientific American 97, 19, 322 (November 1907)