Modeler’s Corner

| August 2007

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    Tom Jamboretz’s model hit-and-miss engine.

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Bar and flat stock hit-and-miss

I have been collecting old engines for about six years and am a member of the Illinois-Missouri Tractor and Engine Club in the St. Louis area. The more gas engine shows I attended, the more I knew I wanted to make a model hit-and-miss engine. Most of the choices I found were casting kits made by many different people from all over the United States and the United Kingdom.

I finally ran across a hit-and-miss engine that was made using bar and flat stock. It has a 1-1/8-by-1-1/2-inch bore and stroke and no castings. This was a big advantage to me, as I did not have a milling machine at the time. All I had was a small lathe and a drill press. The engine was designed and drawn by Harold Depenbusch in Kansas, and came with instructions, drawings and a parts list. There were a few parts I purchased, such as gears and a miniature spark plug.

I started with the base, which is made from 3/16-inch sheet plate and heli-arc welded together. To this I added the iron cylinder and surrounding water hopper. These I tack-welded and sealed with JB Weld for a watertight hopper.

The head is made of aluminum with the 7/16-inch valves of stainless steel. The valve seats are actually cut in the aluminum head with mild steel guides and then lapped to give a good seal. The piston and rod are also aluminum with two cast iron rings from Otto Engine Works.

The biggest challenge to me, the non-machinist, was the one-piece crankshaft. It is made from a piece of 5/8-by-2-3/8-by-8-5/16-inch flat cold-rolled steel. After laying out the centers and sawing away excess metal, it went onto the lathe to machine the throw. I had to make a long reach cut-off-type tool to reach the throw. It worked surprisingly well.

After making the rest of the parts and reassembling, I had a hard time getting the model to run the way I wanted. However, it came around after a long thought process and help from a friend in Oregon. It turned out the exhaust camshaft was made wrong, so I needed to cut a new one to bring the exhaust valve timing to the correct position. I did deviate from the plans on occasion, such as changing it to run on propane (which required a demand regulator to be made) and putting the ignition point on the other side of the engine.


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