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Pete Wood,          Rolling Hills Estates, CA           12/22/2006


My second engine is the Joe Tochtrop "economy" engine, built this year and which, as you can see, has yet to be finished and painted. Both engines were built on my Atlas Model#618 lathe and my friends Craftsman 12inch lathe and milling machine.



What’s in the video:

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, the 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”.


Click Here for details, description and schematic for the adjustable engine control module

A video of the engine running with the electronic speed regulator       VIDEO 2 (Windows media file). 

12/31/2006   This engine is my second project after building the Stuart horizontal steam engine. It is a Hit ’N Miss engine designed by Joe Tochtrop based on the Sears Roebuck “Economy” engine of the 1920s. It has a bore and stroke of 1.125 x 1.75 and the castings are aluminum alloy with cast iron flywheels and crankshaft. I bought the complete kit which also includes spark plug, lubricators, mixing valve, caged needle roller bearings, piston rings and valves with brass seats and springs. Most of the construction was done on my Atlas model 618 lathe but the larger pieces (flywheels and base) were machined on my friend’s 12inch Craftsman lathe and milling machine.

 The photo shows the cylinder block mounted to an aluminum plate with clamp bolts, replacing the Atlas top slide. The cylinder is being machined using a home made boring bar with 1/8 inch dia. HSS tool bit.

I made a couple of modifications to the original drawings and instead of mounting the cylinder block to the base by studs in the base, the block now is tapped and 6 Allen head machine screws are inserted up from the base. This saved having to machine the top of the cylinder base flat for the stud nuts.

The supplied cylinder liner material was a piece of black iron welded pipe so I replaced this with 1.125 x 1.250 inch, seamless drawn steel tube which needed only slight honing for a truly parallel finished bore. The compression is excellent and the engine runs reliably down to 100RPM.

The speed control is also changed from a mechanical to a digital electronic control with a solenoid which prevents the exhaust valve push rod closing the valve during the over speed period.

 The photo shows a 3/16 x 1/32 neodymium magnet mounted to the cam gear. Actually its own magnetism holds it in place at any speed so it is very easy to adjust the timing just by pushing it around and using an automotive timing light looking at the crank position. The 3/16 magnet gives a dwell angle of about 40 degrees (crankshaft). The Hall sensor is inside the pink heat shrink tubing and the assembly is mounted to the base using one of the cam plate screws.

The Hall sensor also provides the timing period for the speed control. Both these circuits work great but had problems at first due to interference pulses generated by the ignition coil. By the way, I kept the mechanical governor just for show because I like to watch the weights going around!

The photos show the engine in a semi finished condition. I now have to file the casting flashes off the flywheels and paint it per the original color scheme.



Copyright 2006,  Florida Association of Model Engineers and engine builder as noted above, All rights reserved.