Author Topic: Learnin' Stirlin' - a peculiar looking Stirling Engine (Read 819 times)

Sanjay F · « **on:** June 29, 2026, 07:43:44 pm »

So far on my Model Engineering journey I have built and restored steam engines, had a bit of a disaster with an IC Engine and built a flame gulper but have always fancied a Stirling project.

I've read up on Stirling engines and understand the basic principles and have a major project on the shelf for another time when this very odd looking (some would say ugly) engine came up very cheaply; what swung it for me was its homemade agricultural looks, the fact the radiator looks like a hip flask with a cooling fan and it needs some TLC

I bought the little burner from AliExpress for the princely sum of £1.99 and probably the same for the meths to burn in it. I filled the radiator with water, sparked up the burner and after a while and a lot of smoking smelliness I actually got some movement out of it, however, water started leaking from a few places and the whole thing is tight and needs a good clean to make it run smoother and faster. The burner and the hot water made a nice marks on the woodwork so I question if if should be mounted on wood?

I'm going to dismantle it, clean it up, put the same size bolts in rather than the current random ones (maybe), stop the leaks and find a belt to run the fan; this is only a learning exercise after all.

Finally, I'm going to recycle the old Vulcan beam engine base from my previous build and mount this strange looking object on it...........I think it will look better (questionable) and at least the base will get a new lease of life!

Dave Otto · « **Reply #1 on:** June 29, 2026, 07:55:20 pm »

Wow! Something only a mother could love, or maybe it's creator.

Good luck with the restoration.

Dave

Jasonb · « **Reply #2 on:** June 29, 2026, 08:30:34 pm »

Possibly a Robinson, but I don't think Heath is the one we usually associate with hot air engines

crueby · « **Reply #3 on:** June 29, 2026, 08:35:28 pm »

Neat old engine - don't think I've ever seen a sterling with a radiator and a fan like that. At that size, did it come out of a Reliant Robin?!

Sanjay F · « **Reply #4 on:** June 30, 2026, 07:25:49 am »

I thought there would be various reactions to this one; it's certainly 'different'

Sanjay F · « **Reply #5 on:** June 30, 2026, 03:51:56 pm »

I have dismantled and done some cleaning and we now have some freer movement, you can see the displacer and piston lifing there's compression and now the flywheel is hooked back up it kind of spins

I guess it should be okay to fire the thing up without the rad as a lot of engines don't have them? Mind you they do have cooling fins which this doesn't, I don't want to damage it?

https://www.youtube.com/shorts/jN3p3jbKFCg

https://www.youtube.com/shorts/CVNRMRge0lA

crueby · « **Reply #6 on:** June 30, 2026, 04:18:22 pm »

For short runs its fine. The trick to keeping a sterling running is the temperature differential, so without the radiator the differential will go away after a little running and it will lose pressure changes and stop.

Jasonb · « **Reply #7 on:** June 30, 2026, 04:24:51 pm »

I run my water cooled ones dry and they go for quite a while, you can always blow a bit of compressed air at it.

The bounce as you turn it over is the way you want it.

Now just don't get too excited when it runs and knock the meths burner over. You have a record

Dave Otto · « **Reply #8 on:** June 30, 2026, 04:26:30 pm »

Looks a little bouncy, that is a good sign. Just don't get too carried away with the heat, I have seen a number of them damaged by guys getting carried away with a torch trying to get an engine to run that had issues.

Dave

Zephyrin · « **Reply #9 on:** June 30, 2026, 05:39:05 pm »

some signs of compression inside, a good point although the movement seems somewhat stiff when turning the engine by hand...may be too much oil at many places.
She could make a quite decent model after the repair and cleaning you usually do on all your models!

Sanjay F · « **Reply #10 on:** June 30, 2026, 06:54:01 pm »

This is what it does without cooling, but water in the jacket. I think it wants to go, I may try the compressed air on it and see what happens.

The water leaks are caused by several problems at the joints on the pipework (unsurprisingly). The pipe from the water jacket just pulled out and wasn't fixed but must have been originally soldered in place (red arrow) and I managed to break the other joint while undoing it (blue arrows), but can I can make a longer 5/16" x 32 hex piece which will screw 2 sections together.

My mate who's a plumber has just told me about liquid PTFE which sounds like just the job for sealing the joints.

And yes, precaution with inflammable materials has been noted, the wife is already looking at me dubiously and upping my life insurance

https://www.youtube.com/shorts/2sJuxvNxfG8

Dave Otto · « **Reply #11 on:** June 30, 2026, 07:13:22 pm »

The water going into the displacer rod bushing is not helping anything.
Have you checked the timing? The displacer piston needs to lead the power piston by 90 degrees. The engine will only run in one direction unless you change the timing.

Dave

Sanjay F · « **Reply #12 on:** June 30, 2026, 07:28:18 pm »

No, not touched the timing so its as it came, I'll take a look at that and it felt like it would only turn in one direction. I guessed the water at the top wouldn't help

Sanjay F · « **Reply #13 on:** June 30, 2026, 09:09:57 pm »

Experiment II

I installed some temporary pipework to get some cooling and covered the rad with an ice cold cloth. The displacer and piston are definitley 90 degs apart, but I think the issue is what Dave pointed out before, there seems to be water coming up through the where the displacer rod is, no matter how much I dry it up more comes up.

I presume this should not be the case and the water jacket/displacer cylinder has a leak or there is water in the displacer cylinder which needs removal?

If that is the case then whole thing needs taking apart and finding out where the issue is and resealing; I can see lots of sealant everywhere!

If a complete tear down is required it may be the end of this adventure for now as I want to get back to my Hicks Oscillator; any thoughts about the water around the displacer rod gratrefully received

https://www.youtube.com/shorts/FdCg_a9JizM

Dave Otto · « **Reply #14 on:** June 30, 2026, 09:55:49 pm »

I didn't realize that the water was being forced up from the inside of the displacer cylinder, that make it even worse. I thought that it had just leaked out of the cooling from the outside.
So for sure sure it seems that there is a leak path inside the cylinder that is going to need repairs. At this point I don't think you have any other choice but to tear it down and investigate the source of the water. Also the water being pushed up through the displacer rod bushing like that would indicate a less than desirable fit on bushing /rod.

Dave

Sanjay F · « **Reply #15 on:** June 30, 2026, 10:04:13 pm »

Thanks Dave - I thought as much, and as it's a learning project, all is good.........strangely

Sanjay F · « **Reply #16 on:** July 07, 2026, 12:36:14 pm »

The dismantling has commenced and lots of blue sealant to cut through; I may have found the issue the displacer cylinder was completely full of water and flooded out when I managed to get the bottom off!

This was entirely my fault as I had tried to cool the top of the piston with ice, ice melts apparently when heated (who'd have thought?) and the melt water got sucked into the displacer!

I now need to complete the dismantling including the power piston, remove all the water and then reseal everything; I guess the displacer doesn't need lubrication whereas the power piston should?

Sanjay F · « **Reply #17 on:** July 07, 2026, 02:12:20 pm »

All dismantled an drying out in the afternoon sun.

The displacer has come apart slightly at the seams and I was thinking of soft soldering it, but it's very thin and worried it may distort?

Dave Otto · « **Reply #18 on:** July 07, 2026, 04:01:18 pm »

Soft solder won't work there as it will most likely melt. looks like it may have been crimped, can you tell how it was constructed originally?
The only lube needed for the displacer is on the rod where it passes through the bushing. Also if that excessive sealer was rubbing on the piston that is not ideal because of the added drag.

Dave

Sanjay F · « **Reply #19 on:** July 07, 2026, 04:06:31 pm »

Maybe crimped I’ve added another picture, also other areas are soldered but I think they are thicker. Question is does it need to be repaired and sealed to function?

Sanjay F · « **Reply #20 on:** July 07, 2026, 04:08:51 pm »

Actually couldn’t I use a bit of JB Weld?

Sanjay F · « **Reply #21 on:** July 07, 2026, 04:14:43 pm »

Sealed 👍😀

Jasonb · « **Reply #22 on:** July 07, 2026, 04:20:18 pm »

Looks like the split goes a bit further clockwise in the last photo

Sanjay F · « **Reply #23 on:** July 07, 2026, 04:32:23 pm »

Good spot

PaulR · « **Reply #24 on:** July 07, 2026, 04:44:35 pm »

Quote from: Sanjay F on July 07, 2026, 12:36:14 pm

I guess the displacer doesn't need lubrication whereas the power piston should?

That's right, don't get oil into the displacer cylinder.

Dave Otto · « **Reply #25 on:** July 07, 2026, 05:04:04 pm »

There will be a temperature gradient across the height of the piston, of course the bottom will be much hotter than the top. The JB weld my hold up, will be interesting to see.

I have always been under the impression that the displacer pistons need to be air tight, and on some plans you are told to pressure test them by submerging it in hot water and check for bubbles. However there are some designs where the displacer can act as kind of a regenator and the air can flow through the piston which contains some material like steel wool. I think the Robinson engine is this way. A couple designers of model hot air engines here in the US (Brad Smith and Paul Jacobs) maybe others, used a grill cleaning brick as the displacer piston on their scale models. I have at lest one of these designs in my collection, the Bremen Caloric Walking Beam engine.

Dave

Sanjay F · « **Reply #26 on:** July 07, 2026, 05:46:24 pm »

I haven't got any but there is a high temperature JB Weld. I thought it best to seal the displacer it as it was originally sealed and it's quite involved taking apart again.

While the JB dries I'm going to connect up the radiator properly. First thing is to clean up and resolder the threaded part on the top part of the cylinder; then use the existing 5/16" threaded hex piece to connect the rad to the top of the cylinder.

Secondly I'll make a longer 5/16" threaded hex piece to connect lower part of the radiator and cylinder together sealing them both with the liquid PTFE

Alyn Foundry · « **Reply #27 on:** July 07, 2026, 07:42:23 pm »

It looks like a crude attempt at metal spinning? I made several chucks and parts over the years. Brass is quite forgiving so long as it has adequate soap and Paraffin to ease the working.

As for the split I would roughen the surfaces and apply a film of Acetate cure Silicone it’s remarkably heat tolerant.

Our own Robinson model uses a displacement piston that is stuffed with stainless Steel wool that serves as a regenerator.

Graham.

Sanjay F · « **Reply #28 on:** July 07, 2026, 08:22:47 pm »

Quote from: Alyn Foundry on July 07, 2026, 07:42:23 pm

It looks like a crude attempt at metal spinning? I made several chucks and parts over the years. Brass is quite forgiving so long as it has adequate soap and Paraffin to ease the working.

As for the split I would roughen the surfaces and apply a film of Acetate cure Silicone it’s remarkably heat tolerant.

Our own Robinson model uses a displacement piston that is stuffed with stainless Steel wool that serves as a regenerator.

Graham.

I had to look up metal spinning! Quite an art, I'd never seen that before - I can see why you think it was made that way.....

I finished making the connector for the bottom of the rad and will solder the threaded pipe piece into the top of the cylinder tomorrow. I can't make anything water tight atm until I know it's not going to have to all come apart again!

Jasonb · « **Reply #29 on:** July 07, 2026, 08:27:11 pm »

The twin tube "original formula" epoxy JBWeld will take a higher temp than that "high temp" putty

Dave Otto · « **Reply #30 on:** July 07, 2026, 08:43:37 pm »

I just finished up the alcohol burners for a couple 1/2 size Lake Breeze fans I'm working on, pretty pleased with how they turned out for a first time go at it.

Dave

Sanjay F · « **Reply #31 on:** July 07, 2026, 08:52:41 pm »

Wow, Dave you should be pleased they look incredible; so many skilled people here, with skills I've never even heard of!

Dave Otto · « **Reply #32 on:** July 07, 2026, 08:57:16 pm »

Thanks Sanjay!

Charles Lamont · « **Reply #33 on:** July 08, 2026, 10:01:51 am »

Another interesting restoration job that seems to be coming on nicely. May I suggest the performance could be improved by fitting some insulation material between the brass flange and the lower steel parts. Something like thick gasket material. This should reduce the amount of heat getting to the water jacket.

Sanjay F · « **Reply #34 on:** July 08, 2026, 01:04:24 pm »

Sounds like a good idea, I have some thick gasket material, let me take a look

Sanjay F · « **Reply #35 on:** July 08, 2026, 03:29:28 pm »

Made a bit more progress today, smoothed off the JB Weld repair on the displacer piston, repaired the top connection to the radiator, started reassembly of the bottom half of the engine sealing as I go. My goodness that blue stuff gets everywhere!

I made a thick gasket as suggested. I had one piece of the thick stuff left which was just enough to fit, my gasket punches were having trouble getting through it I think they may be worn

Sanjay F · « **Reply #36 on:** July 08, 2026, 07:22:32 pm »

Here is the 1st run of engine......woo hoo................. and all was good until I noticed the wetness around the displacer rod again and the engine getting slower and slower!

https://www.youtube.com/shorts/cn3mU1BAiW0

I figured there must be a leak between the water jacket and the displacement cylinder so I dismantled everything and did what I should have done before assembly which was to fill the jacket full of water and watch for leaks ..........I thought I might see a drip here and there, but watch the video below .............it's a torrent!

<a href="https://www.youtube.com/watch?v=F8rkDdD55Ik" target="_blank">http://www.youtube.com/watch?v=F8rkDdD55Ik</a>

On further inspection, I have found the cause of the leak 'there's an 'ole yer pipe, guv!'

Take a look at the picture below where I've circled it, you'll be able to see it. So I mistakenly blamed myself for the water filled displacer whereas it was this hole all along; the only way I can see of repairing it is letting the entire thing dry out in the 'warm' weather and then getting a bit of JB Weld in there and then gently smoothing it out?

Given the engine runs even when water-logged I'm holding out hope that this engine will be runner ......... at some point!

Dave Otto · « **Reply #37 on:** July 08, 2026, 07:37:49 pm »

Congrats on getting it to run!
If that is the bushing that the displacer rod runs through, you might be able to bore it out and loctite a new bronze bushing in place. don't remove the entire bushing, just maybe half of the diameter.

Dave

Sanjay F · « **Reply #38 on:** July 08, 2026, 08:29:36 pm »

Firstly I'm glad I found the problem, I'm not good with mysteries!

I think I'll see how the JB Weld goes and it that doesn't pan out I'll take it from there and look at boring it out. I think I'd have to drill it out and ream it as there's no way I can see to get it mounted in a chuck for the lathe as the jacket has been soldered on good and proper!

Sanjay F · « **Reply #39 on:** July 12, 2026, 11:20:05 am »

The JB Weld didn't work, the wall of the bush is too thin for it to take and when I sand it just drops out

I will partially drill out the bush and see if I can loctite a new piece of round in there but I have a feeling I'll take out the entirety of the bush wall and leave just the 2 end wider sections onto which I can loctite the new bush?

I have sketched what I think the bush cross section looks like, I could well be wrong and the section with the hole in it could be just a single thin section of the bush?

Jasonb · « **Reply #40 on:** July 12, 2026, 01:10:36 pm »

Or it could just be parallel and years of water sitting in the jacket have rusted it away which is why you now have an ever increasing hole.

Sanjay F · « **Reply #41 on:** July 12, 2026, 01:16:47 pm »

Yeah true - guess, there's only one way to find out ...................

Sanjay F · « **Reply #42 on:** July 12, 2026, 02:08:40 pm »

I managed to get the cylinder mounted in the 4-jaw and I'm gingerly drilling 1 letter size bigger each time. The original bore was 5/16" (0.313") and I have just put a 0.348" drill through.

I have approx. 1/16" wall thickness left so don't know how much I should leave/carry on drilling (next size up is 0.366"), but you can clearly see the internal hole has got larger so it must've been parallel and just rusted away

The bush is made of mild steel and so should a new one be made of the same material?

Dave Otto · « **Reply #43 on:** July 12, 2026, 04:37:06 pm »

Is you plan to leave some of the original bushing and install a thin sleeve?
I would make it from bearing bronze.

Dave

Sanjay F · « **Reply #44 on:** July 12, 2026, 05:32:38 pm »

Do I make the sleeve first and then install it or do I plug the hole with the bronze and then drill and ream it to diameter? Not sure how to do the first way as I would have thought the sleeve would be too thin in the chuck and collapse in on itself?

Either way I'm just not sure how much of the original bush to leave, I only have approx. a 1/16" wall diameter

Dave Otto · « **Reply #45 on:** July 12, 2026, 05:49:07 pm »

You can make the sleeve fully in the end of a piece of stock and part it off to length, that way you will not harm it by trying to do further operations on it. Drill and ream first then turn the OD taking light cuts with a sharp tool. If you make it a slip fit in the old bushing and Loctite it in place you will not change the dimensions of it.
The current wall diameter of the original bushing is 1/16"? It would be nice if you could take a little more out of it, the sleeve will be quite thin but doable I think. I guess worst case you completely remove it and install a new one.
The most important thing is you need a gas tight seal on the bushing to rod with no friction, Have you checked the size of the piston rod with a mic so you know exactly what size it is? You will only need a 1/2 thou or less of clearance.

Dave

Sanjay F · « **Reply #46 on:** July 12, 2026, 06:23:47 pm »

Went as as far as I dare which was a diameter of 0.396, so the bore needs to be 0.313 which gives me 0.083 or 0.0415” wall thickness for the new bush.

I’ve checked the piston rod and it 0.312

Dave Otto · « **Reply #47 on:** July 12, 2026, 07:09:57 pm »

That should be plenty of wall thickness for your bushing.
Keep in mind that this is one of the main leak paths in a hot air engine, so the tighter you can get it with out binding the better. Oil will help the seal but it is not a cure for a sloppy fit.

Dave

Sanjay F · « **Reply #48 on:** July 12, 2026, 07:55:40 pm »

I think we're there Dave

I used a new tool .............it looks pretty good and a nice sliding fit for the bush, I had to gently tap the last bit and the piston fit feels like it was originally ........I've just applied the Loctite so will leave for now and see how things pan out in the morning.

Thanks for the help

Dave Otto · « **Reply #49 on:** July 12, 2026, 08:23:41 pm »

That look great Sanjay, nice work!

Dave

Sanjay F · « **Reply #50 on:** July 13, 2026, 02:25:44 pm »

Sadly, I could not get the engine to run, maybe my close fit was not as close as I thought and needed; I think I may have to re-drill it and start again

On the plus side, there are no water leaks and I know the construction method now

Sanjay F · « **Reply #51 on:** July 14, 2026, 01:41:43 pm »

3rd attempt

I drilled out the bush again and made another and this time its tighter around the piston rod so let's see what happens.....

Sanjay F · « **Reply #52 on:** July 14, 2026, 08:03:56 pm »

Third time lucky

Its working with the new bush and I replaced the gasket holding the power piston to the cylinder and sealed around the fixing holes as they went straight into the displacer cylinder!

Yes it's leaking water from the radiator jointing, yes it needs a bit more running in, yes it's still not the prettiest engine, but its definitely getting faster towards the end of the video.....I'll seal off the leaks put a thin metal plate on the wood which is now burnt to a crisp and call it a day

EDIT Must get down the motor spares shop and buy a fan belt

https://www.youtube.com/shorts/_djeYKDWr7Q

crueby · « **Reply #53 on:** July 14, 2026, 08:56:53 pm »

Its alive!

Dave Otto · « **Reply #54 on:** July 14, 2026, 09:50:02 pm »

Congrats!

Sanjay F · « **Reply #55 on:** July 16, 2026, 04:54:38 pm »

The strange stirling engine is now mounted onto a base and is running a lot better and no water leaks. After hours of experimentation I concluded the fan is purley decorative; the belt is either so loose it comes off or with the slightest amount of tension the addtional friction stops the engine.......... (hours of fun trying though

)

Anyway ................this one's concluded & no beautification for this one I'm afraid

https://www.youtube.com/shorts/Bs2GMjDOOtc

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Author Topic: Learnin' Stirlin' - a peculiar looking Stirling Engine (Read 819 times)