Modeler’s Corner

By Staff
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Left and below: Tom used a 9-inch South Bend lathe to turn the piston and crankshaft of the scale Economy engine.
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'Above: Tom Jamboretz made this Sears Economy engine model from a casting kit sold by Joe Tochtrop, of San Francisco. '
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The finished crankshaft and flywheel with micrometer for scale.

Having finished making a model gas engine from bar stock, I
thought it was time to tackle one made from a casting kit. I
started my search on the Internet, and with Gas Engine
Magazine
and Model Engine Builders magazine
advertisements. There are many out there, but the one I thought
most suitable for a beginner was the one based on the Sears Economy
sold by Joe Tochtrop in San Francisco.

The kit offered is unique in a number of ways. The engine has a
1-1/8-inch bore and a 1-3/4-inch stroke, and is hopper cooled. Most
of the castings are aluminum, with the exception of the 6-inch
flywheels, which are cast iron. Joe also offers many of the other
parts, such as finished mixer, valves and valve seats, spark plug,
oilers, springs, gears, gray iron crankshaft blank, and piston
rings, though I realize some would want to make these from scratch.
The basic kit comes with easy to follow drawings but not
instructions – there needs to be some thought process. The base
price for casting and drawings is $149.

All of the work was done on a 9-inch South Bend lathe and a very
simple mill drill. I started with the two-piece base. This was the
most challenging part as the bore obviously needs to be square to
the centerline of the crankshaft. A lot of thought went into the
setup in the mill, and it came out well. The sleeve was made from a
piece of 1-inch black iron pipe. After machining, it was pressed
into the cylinder bore. I had my friend Cliff McNames hone it to
proper size on a Sunnen honing machine. It could have been lapped
to size if desired. Then the aluminum piston was made to fit the
bore and the two rings were fitted.

I opted for the cast iron crankshaft instead of using hot rolled
steel. Any one-piece crank is a very time-consuming venture.
Special lathe tools had to be ground for the job.

Then it was on to the aluminum head. The important step here was
the layout so everything would fit. All the machining was
straightforward. The 3/8-inch valves could be made in two pieces or
one piece from drill rod, as I did. Also, the valves and seats
needed to be lapped for good compression.

Next were the many small parts that make up the governor. All of
these parts are very similar to all of the Hercules-made engines.
It included lots of fitting together with tiny files. In the end
they all worked quite well together.

I did take some liberties with the fuel and ignition systems. I
went to propane for fuel, which requires a demand regulator to be
made to control the fuel. The ignition design calls for a points
and coil system. However, I had been reading about the Hall Effect
ignition system sold by Jerry Howell in Colorado Springs, Colo.
This involves putting a tiny magnet in the cam gear, which triggers
a tiny sensor to produce a spark through a coil. I decided to go
with that. It does require building a printed circuit board, but
with a little care and the instructions, it was no problem. The
system works very well.

After all of the parts were made, it was on to assembly, paint
and building an oak skid. It took awhile to iron out a few quirks
but it now runs better than I expected. It gave me a great feeling
of accomplishment. I really think that this is a good kit for
beginners to test their skills or for the experienced
machinist.

– Tom Jamboretz

Contact Tom Jamboretz at 416 Larkhill Court, Webster
Groves, MO 63119 • tpj1939@yahoo.com

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