Cole's Hot Air Betsy build

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Nov 24, 2013
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Central Wyoming
As stated in the "General Engine Discussion" I started building Cole's Hot Air Betsy from prints that I received from them a long time ago. Life sort of got in the way and I just recently came upon some of the completed parts and eventually found the prints. After lurking around the forum for some time I guess it is time I contributed something. So here goes. The pictures I've included in this post are photos of the prints, and what has been completed to date. I will try and keep posting the machining from this post onward. Since I decided to make the engine without castings I made the flywheel from a Stuart casting that my uncle gave me and it was too small so I made a brass outer ring and shrunk it onto the smaller Stuart wheel. The base is aluminum from something I gathered up and it had some cross drilled holes so I plugged them with brass as well. Since I have restarted the build I made the cylinder base and am now working on boring and threading it to accept the displacer and compressor cylinders. The thread on those two parts are 40 TPI which is pretty fine for my old eyes but I was able to finish the threads in the cylinder base yesterday. The long rectangular brass pieces are destined to become the compressor and displacer connecting rods. hot air betsy print pg 1.jpghot air betsy print pg 2.jpghot air betsy parts 03.jpghot air betsy parts 01.jpg
Forced to take time to replace some injectors in my pickup so machining has slowed to a stop. I should be back at in a few days.
I wasn't pleased with the original design using 2-56 flat head screww holding the cylinder base plate on so I added 2 each 5-40 allen headed screws and it felt much more stout.


  • Cylinder base plate Second set of base bolts.jpg
    Cylinder base plate Second set of base bolts.jpg
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Original design called for round spaces under the main bearings, I choose to replace them with a solid brass block. I thought about drilling the block to give it a better look but have not done so yet. I also replaced the round spacers under the cylinder base plate as well.


  • Drill rod spacers under base plate.jpg
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I had a nice piece of aluminum to machine the finned cooler out of and it was much larger diameter than the drawing so I made it 2-5/8 rather than 2-7/32". I figured a little more cooling wouldn't hurt and I hated to see it go away as chips.


  • Finned Cooler machining (7).jpg
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