Full-scale Economic model

Modeler's Corner


Thomas Burgess's full-scale model of an Economic Motor Co. engine.

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About 10 years ago, while traveling on business, I found myself wandering through a downtown tourist-oriented shopping mall. I was attracted to a small antique shop which proved to have nothing of interest except there, in a glass case, was a Sept. 8, 1883, issue of Scientific American magazine with an engine I had never seen before on the front cover. This I could not resist.

Unraveling the mystery
The engine was described as an Economic Motor Co. engine rated at 1/2 manpower (1/20 of a horsepower), also available in sizes up to 1/2 horsepower. The engine was of noncompression design with a flame ignition. I later discovered that this was the only non-compression engine designed and manufactured in the United States.

Fuel for this engine was illuminating gas, which was available in most large cities. It was manufactured from coal and also known as coal gas. The BTU content of this and similar gases was 1,000 BTUs per cubic foot or less. Illustrations in the magazine showed a rubber hose connecting the engine to a gas lamp on the wall. I recently discovered a patent covering a carburetor for operating this engine on gasoline.

Getting to work
The magazine lay in its protective cover for three or four years while I contemplated how I would obtain this engine. I slowly came to the conclusion that the possibility of any surviving engines was so poor that I had no chance of obtaining an original. The logical conclusion was that I must build a model, but I wanted a full-size engine. My preference was to build one that I could transport to shows without help, but this was complicated by the feeling that the engine would not be historically accurate if displayed on a cart. Another thing influencing my decision was foundry location. The nearest foundry I could locate that would do cast iron was over 400 miles away, while I had a friend with an aluminum foundry only 70 miles from home. The obvious conclusion was to build it mostly from aluminum.

A draftsman and I worked out the dimensions of the engine by scaling items that we recognized in the magazine drawings. This gave us a flywheel diameter of 21 inches. I also obtained copies of four patents filed by a man named Hopkins, which provided additional details on the construction. With this information, the draftsman produced a set of drawings for the major parts. The engine size I decided to make was the 1 manpower version.

Making the patterns
Next came pattern making. The base was fairly easy to make, using plywood flat parts and curved parts cut from cardboard tubing, Bondo and polyester resin, and lots of sanding. The frame was next with plywood parts machined on a Bridgeport mill, more Bondo and more sanding. The flywheel rim provided more of a challenge as no machine was available to build a 21-inch diameter. The problem was solved by making two halves on a CNC milling machine and joining them; the spokes were machined from wood on a Bridgeport mill and the hub on a wood lathe. The real challenge was figuring out how to make a pattern for a cylinder with 12 vertical fins. The first try was a lost plastic foam casting. A fin pattern was produced on the CNC for each end of a block of plastic foam, and a hot wire cutter was used to cut the foam. This did not work well and after several tries only one good part was produced. An aluminum casting was made and sleeved with a piece of hydraulic cylinder tubing with an inside diameter of 3 inches. This bore size proved to be too large when assembled into an engine. When the engine fired, the cylinder pressure was so great that the engine jumped each time it hit and the engine would simply walk off the table if not restrained. A different approach to building a cylinder was necessary.

Working with wax
It was decided to try lost wax casting. A 14-piece mold was machined on the CNC consisting of 12 pieces containing the two end plates for the fins, 32 pins and fasteners. One of the endcaps features a large hole for the introduction of the melted wax. Molding the wax requires that the mold be completely dissembled, sprayed with mold release, reassembled, heated in an oven and placed in a lathe. With the lathe spinning at low speed, melted wax is introduced through the open end with centrifugal force forming a round center bore. The lathe is then left running while the wax solidifies. The mold is then dissembled and the finished wax is ready for the casting process. All this is required for each piece produced.

The same approach is used to fabricate the beauty ring for the top of the cylinder, but only a two-piece mold is required. The wax molds were then shipped to a casting company and cast in malleable iron.

Smoothing the cylinder
The cylinder bore was not smooth and had to be turned to the correct diameter. Trying to obtain a chatter-free, 13-inch- long bore proved impossible until a very heavy 2-inch diameter boring bar was fabricated. The finished bore was 2-1/2 inches, and when coupled with a shorter stroke provided a much improved engine operation.

Improving the ignition
The ignition system was the one place I thought a deliberate deviation from the original was necessary. The original used a trap door about 3 or 4 inches up the cylinder allowing the trap door to open after the piston passed and sucking in a flame from a burner to ignite the charge. This, of course, slammed the trap door closed during the power stroke. All this was designed for an engine running fairly fast under load with no possibility of allowing the operator to make a significant change in speed. There was no governor on this engine, just some simulation of a hit-and-miss operation as the engine sped up to a point where the mixture became too lean to fire.

The low BTU gas the engine was designed to run on also had an effect on the ignition point in the stroke. A variable firing point was required if I wanted to run the engine slowly and with no load. This also compensated for the higher BTU content (3,000 BTU) of the propane fuel. This dictated a more modern spark ignition.

A micro switch was mounted under the crankshaft on a slotted mount, and a screw head protruding from the crank throw provided the cam for the switch. A spark plug in the head with a buzz coil battery and switch complete the ignition system. This proved to work very well as the firing point is approximately 1 inch up the cylinder and the engine has operated continuously at speeds as low as 27 RPM.

Yet another challenge
One more challenge awaited – the surge bag for the gaseous fuel. This device allowed the engine to intermittently pull a rapid surge of gas that was actually flowing into the cylinder faster than the gas pipe could supply. It averaged the flow through the pipe without restricting the flow to the mixer during the intake portion of the stroke. A custom molded part was out of the question because of cost. I obtained some natural rubber with a thickness of 0.020 inch and produced two patterns, one having about a 1/4-inch border when the smaller piece was laid on top. This border was very carefully folded over the smaller piece and cemented with super glue. Brass inserts were machined and attached by inserting in the openings at each end of the bag. These were wrapped with strips of the same rubber coated with super glue. This has proved to be amazingly durable as the bag has been accidentally over inflated on several occasions. In normal operation the bag inflates only slightly with no stretching of the rubber.

Final thoughts
The engine was given a coat of epoxy primer and painted with a gloss black urethane paint obtained from an automotive paint store. I have found this to be very satisfactory with no chipping or peeling.

The engine has operated well at several local shows and at the North American Model Engineering Society show.

My version of why the company failed is that even with a name like Economic Motor Co., its product just was not economical, especially when compared to a compression-type engine such as 4-stroke cycle, which, with the exception of hot tube designs and some designs with the flame introduced through a valve, did not require a flame for ignition.

The only information I have been able to obtain on this company came from the magazine and from the patents. All modern notes about this company seem to be from the sources I have referenced. If any reader has additional information please contact me.

I wish to thank Lee Evans for a great job on the drafting, Ross Bonner and Wade Bonner for the CNC work, and Steve James for the cylinder boring. I am also indebted to the aluminum foundry for their efforts. Without the help of these folks it would have been a much more difficult project.

Contact Thomas Burgess at 9 Belle Meadow Ln., Little Rock, AR 72210 •  tburgess@powertechnology.com