Homemade Stainless Steel Hot-Air Engine

hot air engine

After the initial success of the first engine, it seemed like a good idea to make another engine - bigger and better.

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I started collecting antique engines about 1984, after I attended a Pioneer Day Celebration at Barberville, Florida. Those old engines fascinated me, and I decided that this would be an interesting hobby.

Eventually I bought, sold or traded some 25 engines. Since I didn't have much space in my garage, it was necessary to trade or sell some to get more interesting ones. It was soon evident that all these heavy 'toys' were getting too difficult to handle.

About this time a friend of mine, Alan Phillips, gave me some reprint catalogs of early Sterling Cycle engines. After reading this literature I decided that I must have a hot air engine. Unfortunately, none could be found locally. The only course of action left was to construct my own. The only information available was several cut-away views in the reprinted catalogs, so this is where I started.

Fortunately, I had previously taken a very comprehensive welding course at the local community college. For some reason or other my fascination with working with stainless steel led me to try to make a model of stainless steel. My first attempt took approximately three hundred hours. Of course, since it was a trial and error operation, it goes without saying that I ended up making several parts more than once! The first power piston was not properly sized in relation to the displacer. The little engine tried to run but just couldn't get going. Dilemma-make it bigger or smaller? On a hunch, I made it smaller and the engine ran. Success at last, what a rush!

I polished all the parts and took the engine to Zolfo Springs, where it was a hit. Lots of offers to buy, but when you put so much effort into something, you don't want to part with it for any amount of money.

After this initial success it seemed like a good idea to make another engine-bigger and better. So, back to the shop and engine number two began to take shape. This one is also stainless steel and has precision ball bearings in the rod ends as well as the main shaft. The first engine had needle bearings for the main shaft and pins for all the rod connections. As I was now an 'experienced' hot air engine builder, this one took only about half the time to complete. I finished this one by bead blasting to get a nice satin finish.

I was now on a roll and decided to make an even bigger and better engine. It took a while to gather all the materials, especially the large diameter pipe for the flywheel rims. I ultimately had to splice and re-form smaller pipe to get the size I wanted. This engine is a real 'high tech antique.' The main bearings are double row, self-aligning ball bearings. I calculated the output at approximately 1/8 HP at 300 RPM. As always, it is all stainless steel!

After a few months 'off,' I needed another project but not another Sterling engine, so the old thinking machine started to work and I remembered a miniature vacuum engine I had seen five or six years ago. I just happened to have an article describing a 'Flame Licker' engine. Since I don't like to copy directly, I changed the design details quite a bit. Again this engine would be made of stainless steel. It was a decision that I would come to regret. Stainless steel is difficult enough to work, but in miniature i.e., very small holes to tap-it becomes almost impossible! However, it was well worth the effort to see the little engine run. It is a good runner and makes a neat sound.

Somewhere along the way I acquired a book about Free Piston Sterling Engines. I had been toying with this concept for quite a while and finally decided to try to make one. My first attempt was less than successful (Translation: it would not run). More time was spent trying to make it run than it took to build. Once again my friend, Alan Phillips, provided the clue. He said, 'The power piston must be much heavier than the displacer.' I made a new piston and it finally ran. This was a crude prototype, so I didn't finish it. Who wants an engine with a BRASS piston?

That s right, the newest creation would have to be all stainless steel! This engine ran successfully the very first time heat was applied. It is about 15? inches high, and is very, very quiet running. As with all my engines, propane is the fuel of choice, because it is clean and convenient.

All things considered, I had a lot of fun building these models. I am looking forward to the next project, but don't know what it will be at this time. However, one thing is certain-it will be made of stainless steel!!!