tions of the motor on the part of the foundation is apt to be amplified by the elastic support of the boat's body. Accordingly, the oil engine in a submarine has to have a certain measure of mechanical adaptability, and adaptability all too often means leaky stuffing boxes and valves, and the breaking of working parts that may heat or be subject to unequal stresses.

Expert opinion generally is agreed that the internal combustion engine, especially for under-water craft, calls for the nicest kind of workmanship-indeed, for more careful and skillful fabrication than the best of steam engines for kindred performances. Recognizing this, and knowing the puzzling problems which alternate heating and chilling of parts of the oil motor impose, it is not hard for us to recognize what the engineering world has had to battle with in meeting the exacting conditions demanded by submarine navigation.

Just the same, the builders of these heavy-oil engines are progressing steadily, and to-day, they are able to turn out units capable of developing more than a thousand brake horsepower. Indeed, the Fiat-San Giorgio of Spezia, Italy, has built a Laurenti submersible for the German government of quite 1,200 tons submerged displacement, and for this vessel they have produced two-cycle oil motors of 1,300 brake horsepower each, which ran continuously for 144 hours at 350 revolutions. The Fiat engines are well known for their superior qualities. Where the little "Holland" could make about 6 knots an hour this big submersible can do nearly 20, and at a cruising speed of 10 knots an hour can cover with her fuel supply a radius of something like 5,000 miles. All of this has been achieved inside of fifteen years-something that would have been impossible but for the gas engine.

To the builder of successful marine explosive engines who might be induced to try his hand at the construction of motors for under-water boats, a few words of caution are not out of place here. To begin with, headroom in a submarine is of necessity restricted because of the enforced shape of the hull, and a satisfactory engine must therefore be of moderate height. This limitation is demanded for two reasons: First, it must be possible to remove cylinder heads so that pistons can be lifted out for repairs, and, next, the center

of gravity must be kept low. A submarine has her center of buoyancy above her center of gravity in the submerged condition; thus completely reversing the state of things prevailing in a surface craft. Therefore, in order to have the fullest measure of metacentric height the center of gravity must be kept as far below the center of buoyancy as possible. This calls for some very nice arranging of weights. Again, because of the hull shape and the modest beam, there is precious little room between the side of the engine next to the hull, and, accordingly all valves and adjustments must be so placed that they can be readily reached from the main gangway between the flanking engines. All parts must be accessible that need frequent attention or supervision, and the minimum number of parts must serve to make the motor function efficiently. ciency in a submarine is the very keynote of all of its operative mechanisms, and a hitch may be the very thing that might imperil life at a critical moment.

Effi

Although the gasoline or heavy-oil motor is the prime mover for surface work it is no less necessary for submerged operations, because it drives the electric motors, when acting as generators, during the charging of the storage batteries. Again, the capable manner in which it discharges this duty may make all the difference between success and failure in the hour of combat.

A Class in Gas Engine Design.

The instructors in advanced drawing, patternmaking and machine shop in the Brooklyn (N. Y.) evening technical and trade school, Seventh avenue and Fourth street (Manual (Manual Training High School Building), have arranged to co-operate, and it is planned to construct a small two-cycle gasoline engine complete and ready to run. It is planned not merely to copy existing designs, but actually to design one with details suitable for the equipment available in the shops of the school, and it is believed that the design of this engine will be one peculiarly adapted to the requirements of amateurs who may have available facilities to build an engine and who care to do so but are incapable of handling the problems involved in duplicating some existing design worked out for manufacture by special methods.

Even in this day of modern shop systems there are quite a number of manufacturers who consider themselves progressive that do not appreciate the value of inspection. We know of a certain shop, its location has no bearing on the matter under discussion, a shop making on an average of a thousand horsepower in stationaries a month, in which practically every part is hand-fitted by the assembler after it leaves the machine shop. Place two of this firm's engines of the same size and model side by side and attempt to interchange like parts and it cannot be done. Not a single drawing of the many hundred in the drafting room was marked with limits. The only inspection of the parts received, was that of the form and of the machine shop and this was merely a cursory glance to see that they were finished smoothly and true. The result was two-fold. The assembler spent 3 days in assembling an engine that he should have assembled, with carefully inspected parts, made to size, in an equal number of hours. Even the piston rings were not true or a fit to the cylinder and they were spotted with lamp-black and filed on their periphery to a fit. There was no such thing as an interchangeability of parts. The customer buying a repair part was compelled to fit it himself, and if he did not possess the necessary mechanical skill he was very likely to make a sorry job of it and get poor service from the part as a consequence.

Incorporating a system of inspection should begin with the drafting room, each part marked with limits, so many thousandths of an inch above and below the standard size which will permit it to pass the inspector.

The inspector should be a first-class mechanic himself, and not a boy trained to the job, one who very likely has little or no mechanical skill. He should be instructed to send back to the machine shop or to the junk pile, as the case might be, any part that was not machined to within the limits prescribed on the drawing. At first such a system will, doubtedly, incur losses, but in the end it will be found a profitable innovation. The time saved in the assembly room alone will more than pay for the cost and the added care required for machining of the

un

parts. The engine can then be bolted together without any preliminary fitting by means of a file, a chisel, or an emery wheel. The product itself will be more satisfactory to the customer once he realizes that when a part is broken or worn out, it can be replaced by another that will go in the place of the old one without fitting and will be of the right size and properly located when put in its place.

It might be remarked that working to limits and rejection of imperfect parts is too expensive. This is by no means true as the experience of many a factory has proven.

The inspection should, however, be carried beyond the machine work performed in the plant itself. Every part purchased from outside firms, no matter how reliable the firm has proven in the past, should pass through the hands of the inspector before being placed on the stock room shelves. This inspection should take place as soon as possible after the receipt of the material. Then there is time to have the defected material replaced before it is required by the factory. Should the material be placed on the shelves without inspection and found, when issued, to be below the standard, it results either in expensive delay or the use of material of inferior grade in the finished product.

No factory is too small for careful inspection and it is a wise thing for a manufacturer starting out with a new product to have all the drawings marked with limits and to install a rigid inspection system from the beginning.

Start your product on the market in such a way and it will soon get a reputation for accuracy and excellence, both in design and construction. The ultimate value of careful inspection is beyond question. Lack of inspection and interchangeability of parts makes the engine cost more to begin with and makes it cost more to repair. Interchangeability of parts cannot be obtained without careful inspection. It increases the value of the product from the standpoint of the salesman for the reason that the consumer of to-day has been educated to the desirability of such a system and demands an engine built in this manner.

In the transmission of the many millions of cubic feet of natural gas passing through thousands of miles of pipe lines from the wells to the consumer, it is necessary to raise the gas to a pressure of 300 lb. or more in order to transmit it with facility. It is for the purpose of driving these large gas compressors that the National Transit Company, of Oil City, Pa., has developed the type of engine shown in the accompanying illustrations. These engines are built in units from 300 h.p. to 1,400 h.p. in the horizontal double-acting tandem and twin tandem types. dimensions of the engines run as follows: 17x26, 19x36, 20x36, 25x36, and 24x48.

The

The engine shown in the accompanying illustrations is a 20x 36-inch horizontal tandem double acting engine of 450 B.h.p., having a normal speed of 125 r.p.m. It is a 4-cycle type with side crank, a type of crank coming into quite extensive use in the United States, although finding very little favor in Europe. This is one feature of large American gas engines that shows American engineering to be untrammeled by European practice. The

half-tone Fig. 1, shows a quarter side view of the engine, showing the valve mechanism. Fig. 2 is an end view looking toward the crank, while Fig. 3 shows a close view of the valve operating mechanism. Fig. 4 is a line drawing showing a plan view of the engine in section and a side elevation. Fig. 5 is a vertical cross section taken through the valve. Fig. 6 is an assembly view of the igniter and air starter

mechanism. Fig. 7 shows an assembly drawing of the automatic shutoff. Fig. 8 is a diagram of the valve setting and Fig. 9 shows typical indicator diagrams taken from this engine.

A noticeable feature of this engine is the similarity of like parts in different parts of the engine, for example, both the

Fig. 2.

cylinder castings are identical as are the piston and the cylinder heads. Referring to Fig. 4, the engine is built up with three guide frames, 3, 9 and 11. Cross-heads running on bored guides support the pistons and relieve the cylinder walls of pressure due to the weight of these parts. Each cross-head is provided with adjustable babbitt-lined shoes. The cylinders are supported between the main frame 3,