March  2014.    

Beneath this photo of the cylinder block from a model tugboat engine is a gallery of color photographs of various miniature engines that I have made over the past 17 years.

Keep an eye out for highlighted text that you can click on for more information and larger or additional photos. Leaving the mouse pointer on top of a picture or button for more than two seconds will sometimes yield abbreviated descriptions or comments, but these will be brief.

The pictures presented here have been scanned at 300 dots per inch. Most were 4 x 6 inch prints, processed at one-hour supermarket photofinishers. They have been in my album for years and carried all over the country. I am amazed by the quality of these images on the computer monitor - it provides the perfect lighting which is seldom found when viewing the originals.

Many of these photographs were taken with a Fujica ST-901 automatic 35mm SLR and a 24mm Pentax lens. On occasion I used a Pentax Spotmatic manual camera body. Film ranged from Kodak to K-Mart (Focal).

                Birmingham Dribbler

This is a Carpet Engine - a model of a model. These were the toy trains of the mid-Nineteenth century. They loosely resembled the locomotives of the day and were constructed entirely of brass. This one is called the Birmingham Dribbler. It was made from a package of castings and materials that I purchased from Maxwell Hemmens in Thorganby, England. Mr. Hemmens told me that they were dubbed "dribblers" or "piddlers" because of the wet trails left behind as they lumbered across the living room carpet under steam.

A model mill engine steam plant with dynamo

This engine was made from a set of Stuart Turner S50 castings.
The flywheel is 3 3/4 inches in diameter. 5/8" bore x 1 1/4" stroke

The mill engine is coupled to a Cornish boiler fashioned from silver-soldered copper. It is 2 1/2 inches in diameter and the flue contains 16 Galloway tubes. The riveted exterior is only a decorative cover not attached to the pressure vessel. There are six miniature lamps on the model, as well as a working voltmeter and pilot light. The control panel houses a voltage regulator to supply a precise 3-volt output. The plant is capable of powering a radio at room filling volume at a fairly slow shaft speed.

Alcohol-Powered Engine

Here's an internal combustion engine that was made from a few pennies worth of leftover materials from my workshop. It's an experimental unit that I made to test my skill on several machining operations and to try a homemade threading attachment on the Taig micro lathe.

The displacement is approximately .05 cu. in. and the base is about two inches square. The throttle return spring is actually the fuel line. It is made from silicone rubber and just pushed on with a little bit of a counterclockwise works like a charm!

No, I didn't make the glow plug, I bought it at the corner hobby shop.

A model boiler in the making:
A four-pass unit modeled after a present-day prototype - Cleaver-Brooks CBH-70

I was fortunate in having a good friend who was installing a real one of these units in his family's laundry business. I was able to get dimensions and other important information from him at the end of each day over lots of cups of coffee and tea. Many thanks Bruce!

The boiler is three-inches in diameter and designed to operate at 50 P.S.I. The prototype is fired with heavy oil, but I chose to burn propane gas in the model.

Here is the finished model boiler


The original design of using a swinging link to achieve straight line motion in the piston rod is usually credited to Oliver Evans.

My model was made from odds and ends and operates quite smartly at a steam pressure of only four pounds per square inch. The engine itself is about five inches long and the boiler is one and three-quarters inches in diameter. This was an early project for me, constructed before I bought my first lathe. Any turning was done in the chuck of a hand drill with a file ...not a practice that I recommend!

That's my Dad standing in the background - he passed away in 1993. He was always interested in planes, boats and engines.


Actually a steam reaction turbine, the Aeolipile was invented by Heron of Alexandria in the first century A.D. It was described in detail in his book Pneumatica.

A fire beneath the cauldron boils water, producing steam which is conducted through one of the copper elbows to the pivoted brass sphere. This steam issues from nozzles at the ends of the two small opposing arms on the sphere causing it to spin.

This little replica spins practically silently at 1500 RPM with a steam pressure of only 1.8 pounds per square inch.

The prototype of this steam sawmill engine was designed and built in my hometown circa 1890.
It now stands at the entrance to the home of a well-respected local antique engine collector.

Seated on a wooden platform to allow clearance under the five-inch flywheels, this replica has been fabricated in one-twelfth scale. No castings were used in the construction of this model. All the parts (including the flywheels) were made from flat metal sheets and bars, silver-soldered together. Much of the finish work was done by hand with a file and sandpaper.

The engine was constructed from photographs, measurements and drawings which I made in the summer of 1996 from the original antique engine.

Practically completed, this miniature steam engine is designed to be operated on 60 - 75 P.S.I. at 100 RPM.

In this front view of the same engine you will notice the boiler in the background with the adjustable-weight, lever- type safety valve on top of the steam dome.

If you look closely, you can see the difference between the two pulleys: the left one has a wider rim, while the other is out farther from the crankshaft bearing to accommodate the eccentric and governor belt pulley. In practice the larger wheel was used for the main drive, and the smaller one for the auxiliaries.

Here is a view of the boiler front. It is a wood-burning HRT (horizontal return tube) unit three inches in diameter. Heat from burning tiny Manitoba Maple "logs" on a stainless steel grate first heats the bottom of the boiler shell, then passes through fifteen flue tubes toward the front, boiling the water. An induced draft from a steam blower in the smokestack keeps the fire burning fiercely.

Note: These shots were taken prior to much of the pipefitting that went into the final plant.

This back view shows the angled blowdown valve and spring safety valve (top at back). This photograph was also taken before the boiler installation. The boiler shell is eight inches in length.


You probably spotted this one on my homepage.

This little project was an early one for me. The spindle turns in ball bearings and the headstock can be swiveled to allow it to be used as a grinder. It was made from aluminum and stainless steel. It is powered by a small 6-volt motor coupled to a three-speed pulley system. The capacity is a one-inch swing and the distance between centers is about two-and-a-half inches. It is a semi-scale model of the well-known Austrian Unimat SL.

Model Builder's 3-inch Sliding Compound Miter Saw

You can sever a wooden clothespin in half a second with this saw. I designed it originally to use an abrasive cut-off wheel to cut that very thin brass tubing and channel stock they sell in the hobby shops. The performance really shines with a woodcutting blade installed. The cuts are extremely fast and clean.

It would be a great tool for building model boats. The green metal base contains nickel cadmium cells to supply electricity to the motor, making it cordless. The motor is no its former life it powered a cordless grass string trimmer.

I won't forget hearing those first sketchy reports of the loss of the Thresher over WKBW radio in Buffalo.
All hands were lost on April 10, 1963.

A fifty-five-pound model of the nuclear attack submarine Thresher.

Length: 60 inches


This marine steam plant uses a twin launch engine made from castings and fitted with a Stephenson Link reverse gear. Powered by a kerosene-fired Yarrow-type boiler, it has two heated stainless steel tanks which together hold a half gallon of water.

The copper boiler has sixty-six watertubes heated by six kerosene wick lamp burners with induced draft. They are are ganged in two banks of three for easy pushrod use with future radio control. The double-walled boiler casing is entirely made of stainless steel.

In addition, there is a feedwater heater, an economizer, superheater, stack dampers, displacement lubricator, stop and throttle valves, manual and engine-driven feed pumps with filter, steam blower, whistle, exhaust steam separator, automatic regulator and safety valve, steam pressure gauge, water level gauge and a stack temperature gauge.

Bore & Stroke: 1" x 7/8" Wt: 28 lbs (wet)


This is a scale model of a 5 hp gasoline marine motor. For many years, Bruce Stewart & Co. produced these and a variety of smaller and larger engines. In the first half of the 20th century a great number of small foundries were producing machines of this type. These two-stroke engines were used in the small boats of the inshore fishery on the Atlantic Coast.

The little motor presented in these two photos is about the size of a baseball and was entirely fabricated without the use of castings. Early Imperials like this one used a standard "jump-spark" ignition, later going to the more waterproof "make-and-break" system.

This model sports a working water pump for cooling and a homemade spark plug. For purposes of display, I purchased the unfinished propeller casting from James Bliss Marine in Boston.

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© John R. Bentley 2001.  All rights reserved.