Gallery, Projects and General > Project Logs
The Return of No. 83, a Hot Air Engine
Brass_Machine:
What a fantastic read. Good job Steve!
vtsteam:
Thanks Eric! :beer: How has the winter been treating you this year? Nasty here!
vtsteam:
Funny thing. I uhh was moving the engine while it was running tonight, and I felt a little bug or ant under my thumb. I let go fast of course, and was kind of shocked there could be an insect anywhere this time of year in Vermont, and particularly on a running engine!
Well, it wasn't a bug after all. It was the sensation of suction and compression 13 times a second coming from a tiny grub screw hole in the side of the bulkhead that my thumb was gripping. In other words, it was a leak!
Oh, man, of course the makeshift of fastening the displacer cylinder with those screws hadn't solved the problem of the (2 thou) oversized hole the cylinder was sitting in! Dumb! :bang: Pressure was escaping around that cylinder, and then out the grub screw hole.
And yet the engine has been running. It's amazing that the power pulses from just heating and cooling air 800 times a minute in a 1" diameter cylinder is so great that it can get around a 1 thou mounting gap, then around the screw threads of a bottomed out grub screw, and yet make itself felt that strongly. Hot air engines are continually surpising. I mean it's amazing they can run as fast as they do based on what's happening internally.
Okay well what to do about the leak? Hmmmm. Well wait a minute, there was a paper "head" gasket (tail gasket?) which should have sealed the rim of the cylinder, anyway, right? So where is it coming from?
Brass_Machine:
--- Quote from: vtsteam on February 26, 2025, 07:27:55 PM ---Thanks Eric! :beer: How has the winter been treating you this year? Nasty here!
--- End quote ---
Has been insane.
vtsteam:
Eric, last snowstorm (not the one last night) took me 6-1/2 hours to plow the driveway with the '51 John Deer M. Normally it takes an hour, or hour and a half in a heavy storm. The stuff that came down was like micro ball bearings, it just compacted and slid under the plow, springing back up after it. And there was nowhere to push it, and the winds, and sub zero temps (Fahrenheit). What a cluster! Haven't seen it that bad in 25 years here!
Well, back to the matter at hand -- which keeps us from going cabin crazy :lol: um, oh yeah the leak....
It was the gasket. I made a new one out of brown paper grocery bag material (yes, I still have a few, just for that purpose). Reassembling the engine, No 83 is now consistently doing 1200 RPM, an improvement of 400 RPM. It's a lot more impressive. Like starting to seem a little scary, since it's unbalanced.
Kind of curious how far I can take this engine. I can think of a few things I'd like to test out. And since the components are easy to swap out (ie. NOT pressed fitted) and it's a reasonable scale (~1 bore power and displacer) it's simple to make alterations. Doesn't take a lot of material.
I had intended (for a couple years now) to make a much larger experimental hot air engine -- I have stainless tubing in both 2-1/2" and 4" dia. sizes, and a lot of other stuff specifically purchased for that.
But I'm thinking changes on that scale are more difficult and expensive to make. I can experiment with configurations on this little one much more easily, and then apply that to the design of the larger one.
So No. 83 might have an interesting future as a test bed. We're not done yet......
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