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Home Model Engine Machinist > Showing Them > A Work In Progress > Head cold from Hell and maybe a Stirling engine

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Old 02-07-2018, 01:07 PM   #91
Brian Rupnow
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Woke up this morning with a great idea.--(No, not that kind of idea I'm 71)--I don't have a small fan to blow cooling air over the cold end cylinder on my Stirling, but I do have a great big old air compressor with enough hose to reach my office/test bench. After good wife gets up I will do some really minimalist fixturing and play a stream of air across the cold end fins while running the engine to see what happens.


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Old 02-07-2018, 02:28 PM   #92
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I'm just down here playing on my cad station until Momma gets out of bed----I'm going to take her to work at 10:00 and then go over to Canadian tire and buy some "Meth Gell" which seems to be jellied methylated spirits in a small container to use as emergency heat source when camping.


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Old 02-07-2018, 04:23 PM   #93
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I must have done something to really anger the machine gods this morning. I picked up a can of jellied methylated spirits with the wick in the can, and set out to see if the engine would run with a lower heat source than the propane torch. The engine tried really hard to run, but never quite made it, neither in horizontal nor vertical position.---So as I am furiously spinning the flywheel by hand and muttering "Run you bastard" under my breath, I hear a crunch and everything stops. Close examination shows me that the 1/8" diameter piston displacer rod is bent. How in heck did that happen?--Pulled the displacer cylinder apart to investigate, and see that the OTHER end has pulled out of the displacer piston. Gahhhhh---What happens next!!! Okay--Quickest easiest thing to do right now is to get some weight out of that stainless displacer cylinder. It's wall is currently 0.045" thick. If I can mount it on a mandrel and take that wall down to 0.025" thick in the lathe, and work a little voodoo on that end that pulled out so it stays together, and make a new piston rod that should get me back to square 1.
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Old 02-07-2018, 07:35 PM   #94
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In one of these pictures you can see the displacer piston in the lathe, on a mandrel. I removed .020" radially so the wall has gone from .045" down to .025" thick for weight savings. The piston was attached to the mandrel with Loctite. Believe me when I say it took seven men and a bulldog to get the mandrel out after the lathe operation. The end which had came off was aluminum, and was undamaged. I loctited the outside diameter, pressed it into place with my arbor press, then went around the circumference every 45 degrees and gave the barrel a good whack with a centerpunch and hammer to securely lock it in place with a mechanical lock.

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Old 02-07-2018, 09:16 PM   #95
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AWRIGHT!!! We have huge success!!! After reassembling the engine with a lightened displacer piston and a new piston rod, I still couldn't get it to run--even with the Propane torch. After multiple attempts and no joy, I thought "What have I got to lose" and squirted a bit of light oil on those ball bearings that I had so carefully removed the seals and grease from.--It took right off and ran like a Prince on the Propane torch. I watched it run for 10 minutes, playing a stream of air from my compressor on the cold end, then took away the propane torch and substituted a cam of jellied meth spirits. It ran another ten minutes . Then I got tired of holding my air nozzle on the displacer and quit doing that, and it ran for another ten minutes. I finally had to take the can of meth away to make it stop.
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Old 02-08-2018, 12:02 AM   #96
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The engine has just passed the half hour test, running in "horizontal mode" as I had hoped for. It doesn't appear to require a cooling fan nor a water jacket. It is running from the heat from a can of "methylated spirits". At this point I am ready to declare the engine completely finished and successful. If anyone wants a complete set of updated mechanical drawings in pdf format, contact me and send $25 Canadian to my Paypal account at brupnow@rogers.com There are 30 drawings, including assembly drawings and bills of material
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Old 02-08-2018, 11:49 PM   #97
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Old 02-09-2018, 02:12 PM   #98
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When I was ultimately successful in a half hour horizontal run with only the methylated spirits for heat I noticed one thing and commented on it in the video. The engine would speed up and then slow down as it ran. It never quit, but the speed changes were interesting. Now after running the engine another 3 or 4 half hour runs, it is running much faster and not intermittently slowing down. I am assuming there were different "high friction" points in the linkages and bearings, that were not readily apparent to me, but were significant to this one flea power engine. The more it runs, the more these "high interference spots" get worn down until they disappear.
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Old 02-10-2018, 03:35 PM   #99
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During the time I was building this engine and posting my progress, someone suggested that it should run with the heat from a "tea candle". I thought--"Oh sure. Maybe one of those test tube and graphite Stirlings would run on a tea candle, but not this one. It's simply too heavy for that."---Well, this morning it proved me wrong. I can hardly believe this myself.


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