my first post

[Shanex-2]

This is my first post . I have a few questions . Why aren't there more model alpha stirling engines like there are gamma stirlings ? Why are diaphragms not more commonly used at least in models ? Can or has an LTD alpha sirling be designed ?

[Ian S C]

Shanex-2, some people have trouble with the ALPHA motors because of the two fitted pistons, although I had no difficulty in my Ross Yoke ALPHA, just the extra time spent lapping the bores, the Heylandt crown on the hot piston is held in place with a high strength, high temp glue, the top of the hot cylinder runs at a good red heat, and alls well.I'v built BETA and GAMMA motors, but must admit that I have not used a diaphragm. I did try a metal bellows arrangement,Ithink it was part of a thermostat from an automotive cooling system, It worked but the stroke was too short. I used it in place of the normal cylinder/piston assembly on my free piston motor, so there was no crankshaft to worry about.
There was a series of articals in Model Engineer a few years back on hot air engines with diaphrams in place of pistons, I'll see if I can find when it was if you like. Ian S C

[Shanex-2]

Yes please Ian S C. I am constantly on the look out for more info. I am in the process of building my next stirling engine . the first one I tried failed for the typical reasons ( too much friction leakage and weight ) . I'm hoping this one will work it is an alpha were as my first one was a gamma. Now that I know where to get bearings ( bearingsdirect.com ) and drillrod ( amazon.com ) I have solved much of my friction problems. my drill press not being true was another. But my biggest problem is of course tight but free cylinders and pistons because I don't own a lathe. I'm trying the 3/4 brass pipe and JB weld trick to see if works . If not then I guess I will be back to trying Diaphagms . Since I have found a good place to get silicone diaphragm material ( mcmastercarr.com ) if this atempt fails all is not lost. I do have a model that I got from ebay it's a gamma ltd stirling engine and it was very informative on how lite everything should be .

[Ian S C]

The article is called Why Pistons by Geoff Bartlett. 1992 Vol 167 no., 3932 part 1 page 567, part 2 page 693 Model Engineer. You may be able to get a copy, or find it at your local library.
Don't know how a JB weld piston will do as a hot piston, it should be OK on the cold side, although you could use a diaphram there. Ideally the thing to use for the pistons is graphite, I'v never done so, I usually use cast iron, but you need a lathe for that sort of thing.
Bearings, I usuallyuse salvaged ones from electronic gear, ie., VHS recorders etc. For bigger ones, you can get skate board/roller skate bearings quite cheap, they are 8 mm bore.
For displacer rods I use 3/16", or 1/4" stainless steel tube, and crankshafts are made of mild steel. If you are transporting your motor any distance its often a good idea to remove the flywheel, this helps to prevent the shaft getting bent, but don't make the shaft too thin. One thing to watch is getting the bearings lined up absolutely spot on, and don't force them onto the shaft, or into the housing that holds them, even if you have to use loctite or similar to hold them in place. Ian S C

[Shanex-2]

Thanks for the info. The JB Weld says it will hold up to 600 f but I dont know if the expantion of the brass and jb weld are similar enough to seal good.

[Ian S C]

Can't help with the expansion rate, my only worry is the friction, I have had thoughts of combining the JB weld or similar with gaphite powder, but I'v never got round to trying. Friction is proberbly the biggest killer of little hot air engines, the other is air leaks. As long as your design is in a similar stile to a known working engine, it should work. Ian S C

[Shanex-2]

well I tried the jb weld and boy do the clearances change with any amount of heat so that wont work. I found some brass tubes that are very close fit with each other so I will see if they will work for piston and cylinders. A friend of mine who owns a jetski shop has a few sleeves from the air pumps on the dfi 951 engines from a Sea-Doo And he has a lathe so I can turn some steel pistons for the sleeves. with a bore a little over 1 1/2 inches that should make some power.

[Ian S C]

i read of one comercially made stovetop motor on the web last night that had a wooden piston with a leather seal. I also found www.jonbondy.com
Another is YRIZLE.COM Ian S C

[Shanex-2]

I liked the jonbondy site. I tried the brass tubes and they work good now I have to make the rest of the engine for them .Im hoping Friday that I will get to my friends shop and put in some lathe time.