The National Company was one of the very first concerns in this country to adopt the 6-cylinder engine for its touring cars. The new 1908 6-cylinder motor, which we illustrate, is one of the most compact engines of this type on the market. It has individual cylinders of 5 inches bore and stroke. The improvements in this engine have been such as to do away with what little vibration there sometimes is with an engine of this type, and also to reduce the noise as much as possible. For accomplishing the latter purpose, large, wide-faced, spiral gears are used for driving the two cam shafts, and the shafts are mounted in Hess-Bright ball bearings of generous size. The cams are especially large, as are also the nickel-steel valves, which have a very small lift, and are thus practically noiseless. The valve lifters have large rollers at their lower ends. The inlet, exhaust, and water pipes have been increased considerably in size, but they are attached to the engine in the same way as heretofore, that is, by a comfnon yoke, which holds both the water (Continued on page 8-46.) Latest Improvements In The Franklin Air-Cooled Engine. (Continued from page 322.) the illustration. The large lower washer is on the exhaust valve, while the smaller washer and spring are on the inlet valve. Each valve is operated by independent rocker arms. The push rods which operate these rocker arms fit into adjustable ball-and-socket joints on the latter. The incoming charge of cold gas makes its entrance through the port, 4, and the inlet valve. In doing this it passes through the hollow exhaust valve, 3, which it tends to cool. About 60 per cent of the burnt gases are discharged through the auxiliary exhaust valve, the result being that only 40 per cent of these gases pass through the exhaust valve proper. As a consequence, this valve does not have the tendency to warp that does the exhaust valve of an ordinary air-cooled motor, and this despite the fact that the valve in this instance is a mere shell. On account of the rounding head of the cylinders, the interior surface of these is the smallest possible. This assures the use in work of the greatest number of heat units in the charges of gas, and, as a consequence, the new engine is more economical, if anything, than the old one. All the valves in the new engine are mechanically operated from a single cam shaft. In this new model, too, the fan is driven positively by bevel gears. The cylinders are oiled by splash lubrication, and a rather high level of oil is maintained in the crank cases by .means of a gear-driven mechanical oiler. Baffle plates are fitted at the base of each cylinder, and these cause the oil to be drawn up by the piston suction through an opening on the working or thrust side of the piston, where it is most needed, and from which point it gradually works around to the other side. Two of the larger types of Franklin cars are this year 'fitted with a gear-driven Bosch hightension magneto in addition to the usual dry battery and coil ignition. The same multiple-disk clutch that was used last year is found located in the flywheel of the 1908 engine. The only improvement which it seems possible to make on this powerful, light-weight motor, seems to be the employment of non-adjustable ball bearings on the crankshaft in place of the plain bearings now used. Perhaps, after another year, this style of bearing will be tried. The National 6-Cylinder Engine. (Continued from page 322.) and inlet pipes on one side of the engine, and water and exhaust pipes on the opposite side. All joints are made with tapered nipples. The plpmg can be quickly removed after taking off one or two nuts. The distributor is now run up between two of the cylinders, instead of being placed at the back end of the engine as heretofore. The water pump, mechanical oiler, and Bosch high-tension magneto are all gear-driven. The magneto is connected to the gear on the front of the engine through a universal joint. It is fastened to the engine by a brass band, which passes over its top, and is held down by a couple of thumb nuts. It is, therefore, very easily removed, if necessary. All six cylinders are provided with two spark plugs, one of which is fed from the magneto, and the other from a single coil and distributor supplied by a battery. The material used in the engine cylinders and pistons is cast iron of an extra strong, special, fine-grained variety. The pistons are made somewhat longer than heretofore. While there are no radical changes, the engine shows many refinements and small improvements conducive to quietness of running, lack of vibration, and long life.
This article was originally published with the title "The National 6-Cylinder Engine" in Scientific American 97, 19, 322 (November 1907)