STUART TURNER S-50 STEAM ENGINE

Since this was my first project, I bought Edgar T. Westbury’s book “Building a Steam Engine from Castings”. Although it describes a vertical engine, most of his hints were a great help for my horizontal engine.

The baseplate was machined on my friend’s milling machine but all the other pieces were machined on the 6in Atlas lathe.

The only changes I made were to the crankshaft and its bearings. The drawings called for drilling and reaming the crank bearing blocks 0.250in and making the crankshaft from ¼ inch CRS. Running a steel shaft in a cast iron bearing did not seem a very good idea so I reamed the blocks to 5/16in and pressed in sintered bronze bushings. Rather than using ¼ inch CRS, the crankshaft was made from a round ¼ inch HSS tool bit. This was exactly 0.250 and had a mirror finish and of course was impossible to machine but could be cut to length and faced with a high speed die grinder mounted on the lathe top slide using a 3 inch cutoff wheel. The drawings also called for the crank web to be attached to the shaft with a 5BA screw but I decided to make it an interference fit on the shaft and then to turn it to size. It now runs perfectly true with minimum friction. The steam engine was an interesting first project which gave me great pleasure as well as some frustration because the drawings were dimensioned in fractions which then had to be converted to decimals for machining and measuring.

One of my most useful lathe accessories is an Atlas milling attachment which I bought on eBay. Many machining operations such as cylinder boring and facing, keyway cuts etc. are a snap with this vertical slide and make the lathe much more versatile.

HIT ‘N MISS FARM ENGINES

Before farm tractors were equipped with power takeoff pulleys in the 1930’s and before many farms had electricity, Hit ‘N Miss  engines were popular for driving hay lifts, water pumps, saw tables and just about anything  that needed a simple engine up to 10HP at constant speed that could run on kerosene or gasoline. Ignition was by impulse magneto and later by battery and high tension ignition coil.

The engine had a single cylinder with an atmospheric intake valve and a cam operated overhead exhaust valve. Constant speed was controlled by a governor that prevented the exhaust valve from closing when the governor sensed an over-speed. This made the engine misfire and also prevented fuel from being wasted during coasting. When the governor sensed an under speed condition, the exhaust valve was allowed to close and the engine resumed normal firing, hence the name Hit ‘N Miss.

This new engine is my own design started in January 2007 and first run this week.

Here are the specs:-

• Single cylinder, horizontal Hit ‘N Miss farm type engine.
• 1.13in bore x 1.75in stroke.
• Swept volume 28.5cc.
• Electronic ignition with Hall sensor and rare earth magnet.
• Electronic speed control with solenoid control of exhaust valve.
• Built entirely on my 6in atlas lathe with the exception some milling of the main chassis done on my friend’s milling machine.
• No castings were used. Flywheels weigh 2 ½ lb each and are 4in diam x 1in wide.
• Piston has 2 rings from Coles Models.
• Chassis is cut from 4in x 2in rectangular steel pipe.
• Fuel tank is integral in chassis.

This engine has been both challenging and rewarding. It took me about 5 months of spare time to finish it during which time my 6 inch lathe handled some quite “innovative” set ups! When first run, it was obvious that the exhaust cam dwell angle was too long and resulted in the water jacket boiling vigorously and the engine having a “sporty” exhaust note. I reduced the dwell to open at BDC and close about 5° ATDC (crankshaft), it is much cooler and tamer now.

Before and during construction, I made a complete set of drawings using Microsoft Visio. I can supply these for a nominal fee to cover postage etc. if anyone is interested. Click here to send me an email.

The “Economy”

The “Economy” engine was sold by Sears Roebuck circa 1920 and the engine shown in the video is a fairly accurate scale model. It was built from a set of castings designed by Joe Tochtrop of San Francisco. The most significant change to Joe’s design is the speed control and ignition circuit. Instead of the breaker points and mechanical governor, my engine uses Hall sensors to provide timing and speed control.

The video shows a top view with the speed control solenoid on the timing side of the con-rod. If you look carefully, you can see its pole piece pulling in when the engine over speeds. This causes a rod to engage a recess in the exhaust valve push rod preventing the valve from closing. When the speed drops, the solenoid releases and the engine fires normally and speeds up again. The speed setting is adjusted by a potentiometer as shown.

Purists would probably accuse me of cheating the original intent to represent 1920’s technology with a high tech solution but it’s really no worse than installing modern plumbing in a historic building. I guess I am not a purist!

Suffice it to say that the engine starts easily, runs smoothly and looks and sounds just like the original “Economy”.

Webmaster note:
Peter has published a paper “SOME CONSIDERATIONS IN THE USE OF HALL EFFECT SENSORS IN IGNITION CIRCUITS”. Follow this link to access it.