Trouble-shooting a new Stirling

[minh-thanh]

My engine
hot cap and displacer is nearly equal the test tube (ID 16 mm), stroke is 18 mm
power piston 8mm, stroke is 18 mm
With your engine, I don't know with piston 9.5 mm is better ?

 

[Harry Mueller]

Found and fixed one air leak. It was a hole I had plugged with a small bolt but it was still leaking air. Anyway, now it’s run up to about 30 seconds and even sped up a couple of times before it stops. Woo-Hoo! I used WD40.

Next I’ll take Minh Thanh’s advice and try sewing machine oil in the power cylinder and the linkages.

I guess I still have an air leak or friction is too high. I’ll have to figure that out.

Harry

 

[minh-thanh]

If you have used the WD 40, clean all parts, then use sewing machine oil, BUT, very little. and very very little in cylinder and connecting rods
Yes , check it again, find friction (The parts need to move smoothly ), gas leaks ( engine should be airtight )and fix. If the engine still does not run for long time, increasing the flywheel size can be solved
Reducing the weight of the bars and connecting parts - your engine is very very low power, it is not necessary to make those parts too heavy , or big
************ If I remember not wrong, piston you made of aluminum?
If so, you can reduce a little piston diameter with 1000 sandpaper (I'm not sure how much it should be, because I don't have the accurate measurement tool measure it). Only a few rounds when you rotate the piston around sandpaper and retry the engine, Do this last after you make sure the other parts are ok . I am not sure it will be right because I do not know the piston you have perfect fit with the cylinder, just a suggestion.

 

[Stirlingking]

Hello Harry Mueller, this is my 1st attempt at a post with this forum.
My 1st Stirling build was from plans found in the July 1965 issue of Popular Science magazine over 45 year ago. I didn't do every thing right but it ran well.
If you can find that issue you will see the displacer displacement is about 1 1/2
times the power piston displacement. I have been designing my engines based on the Pop Sci design but with 1.5:1 to 2:1 displacer to power piston ratio and they run very well.
My engines run fine with the flywheel removed. Total displacer internal clearance of the Pop Sci design is about .5 mm (.020") per side and the displacer to power piston area ratio is about 4:1.
Test the air tightness of the pistons/cylinders separately. I would suggest trying to increase the displacement of the displacer piston and not go any smaller on the power piston. With a bore of 8 mm it's possible bearing friction is a large part of total friction.
The Pop Sci engine has 15.8 mm(.625") power piston bore and stroke and runs well when lubricated with WD-40 or kerosene. The displacer piston is a 19 mm cigar tube with approx 24 mm stroke.
I have been looking for someone interested in building Stirling engines for decades.
I have much more to say. Please excuse the lack of organization of this post.
I hope this helps a little.
- Ted

 

[Cogsy]

One tip that *might* be of use - I have a couple of cheap mass-produced Chinese stirling engines and I only ever use graphite from a normal pencil to lubricate them. I literally just scribble on the rods where they're exposed and they work fine. One of them is an LTD and will run nearly 80 minutes on a cup of coffee,they other is a small twin-flywheel one that I've had over 2200 rpm from with a small alcohol burner.

 

[Harry Mueller]

Thanks again for all the suggestions; this forum and the folks in it are truly a treasure.

I took apart everything except the crankshaft components, cleaned them, added a small amount of oil with a needle and reassembled it. It failed to run at all again. I don’t think this is as a result of using light oil instead of WD40 but rather friction. I think all the leaks have been taken care of.

Perhaps friction on the crank bearing or on the power bearing. I think all the other surfaces are smooth enough to allow the engine to run.

I’m not sure if I can take apart the crankshaft components without ruining the pieces but I suppose I have to try. I will try to sand the piston a little as a first attempt as suggested to get it running again. Using graphite as a lubricant also sounds good. I remember having some that could be blown into a lock that worked like magic. I’ll see if I can find more of that at a store.

Ted, I was really surprised to read that your engine ran well without a flywheel. Based on what I’ve read I thought that was impossible, another indication I have a lot to learn.

I’m still determined to get this engine running and believe with all the help I’ve been given so far, I should be able to do so.

Harry

 

[littlelocos]

The (not so) secret sauce to my Stirling and Flame Licker engines is Kano Kroil from Kano Labs www.kanolabs.com or Amazon. It stands up to the high heat, doesn't get gummy, and is considerably thinner than WD-40.

Piston fit should be gas-tight with no drag. All mechanisms, joints, etc. should also have no drag or tight spots. Here's a quick video showing the piston fit on my Essex Caloric.



Enjoy,
Todd.

Todd Snouffer
Littlelocos Model Engineering.

 

[minh-thanh]

I always remind myself when making some small stirling engines:
- Try to make the bearing and displacer's shaft really fit and move smooth
- Piston and cylinder like you said
- With bearing and drive shaft (flywheel): it may be a little loose - no problem
- With links, connecting bar ... make sure they move smoothly in all directions (may be a little loose - no problem ). Reduce their size and weight
- Make sure everything is aligned when assembling all together
- When assembling all together, don't try to make everything fit , give them little cleft

 

[Harry Mueller]

Wow, there is no way my piston creates that kind of compression.

I doubt I can get a better fit with my cylinder/piston combination. As I got close when turning the aluminum piston, I was turning it down 5/10,000 each pass and testing it. So I’ve got to be within .001 at worst I would think.

Then again I don’t get anywhere near your compression, or that of Minh Thanh. As I reduced the piston size I kept dropping cylinder size by adding brass tubing held in by a couple of o-rings. Perhaps I have a leak there. Or maybe I need your secret oil.

This must be a major clue, I’ll play around with trying to get some more compression. And yes, I’m going to add a bit of slop to the crankshaft, it may be too tight.

Thanks,
Harry

 

[mcostello]

Could pencil graphite be used on connecting rod big ends?

 

[Stirlingking]

Harry, I looked at my post this morning and found a mistake I missed.
I stated the ratio of the 2 displacements in the Pop Sci model being 1.5:1.
I later looked at the blueprints and determined the ratio to be per print at 4:1.
The ratio of the displacements and a proven design are the most important parts of a Stirling engine. Lubrication, fine tuning, adding regenerators (maybe), etc will
certainly help a Stirling run better/faster.
An LTD (low temperature differential) coffee cup Stirling was mentioned. You will notice LTD designs have the ratio in the 30:1 to 50:1 range and can run on the heat of your hand. It is worth noting a low temperature differential Stirling engine is a low power engine. Stirling engines that make usable power and in many cases a lot of power have a high temperature differential and take a lot of heat to run. Experimental engines with the differential "T" too high come near to melting down to barely run, or not at all, as I found in a couple of my builds.
When I build a Stirling with the aforementioned ratio of 1.5 to 2:1 they run like crazy. Then different lubricants are tried to see the difference. I got some interesting lubricant ideas from the other posts. I will be trying them in my next models (2 & 4 power pistons).
- Ted

 

[minh-thanh]

With your engine type and engine size, I think it works well with a piston of 8mm diameter (I tried the 8 -> 12 mm pistons and found that the 8mm piston is the best fit, and of course the smaller the more difficult it is to do . my engine different type your engine, It looks like the image below, I change the power piston diameter and only change its stroke)
With the flywheel, I think I'm wrong because the engine below is smaller flywheel but it still runs. (it has the size and stroke the same of your engine)

All my parts are made of aluminum ! You can combine other materials for better and more beautiful
Your engine has run for 30 seconds as you say and IT WILL BE RUN !
So, the problem you need and focus to solve is friction and air tightness !!!
Video :

 

[Harry Mueller]

The saga continues.

I took apart the crankshaft and main bearing and ran them together in the lathe at high speed with Brasso until the crank/bearing interface was even more polished. The crank now turns as if it’s running on ball bearings.

The old cylinder looked too complicated with all the o-rings so I scrapped it and turned a new one and inserted an 8mm brass tubing liner. The piston fit was perfect and with just a slight amount of light oil, the compression was demonstrably better.

With the two major improvements I though the engine would now run well but I was wrong. It didn’t run at all, as a matter of fact may be worse than any time before.

That leaves the displacer and I’m not sure at this point how to deal with that. The connecting rod bearing seems relatively tight and the O-rings are intact but when I turn the flywheel slowly there is no hint of compression. That tells me there must be a leak of some kind somewhere in the displacer.

I ended up buying 7 or 8 different sizes of test tubes so I may try making a displacer that would give me a higher displacer/power piston ratio. I’ll have to check to see if I have some that might work together as a cylinder/piston combination.

Other than that, I’m starting to run out of ideas.

Harry

 

[minh-thanh]

The saga continues.

The connecting rod bearing seems relatively tight and the O-rings are intact but when I turn the flywheel slowly there is no hint of compression. That tells me there must be a leak of some kind somewhere in the displacer.

You mean: you use the O-ring for the connecting rod of displacer ???? ????

 

[Harry Mueller]

No, O-rings to hold the test tube in the cylinder.

 

[minh-thanh]

The saga continues.

no hint of compression.

I ended up buying 7 or 8 different sizes of test tubes so I may try making a displacer that would give me a higher displacer/power piston ratio. I’ll have to check to see if I have some that might work together as a cylinder/piston combination.

Your problem is no compression, find it and solve it
Higher displacer / power piston ratio: it will make the engine easier to run, but still have to ensure air leakage.
If you want to increase the Higher displacer / power piston ratio, see the ratio of my engine at # 41

 

[Harry Mueller]

I agree, compression is my nemesis. It has to be in the displacer since I also replaced the fittings that the tubing slides onto to ensure they were air tight.

But O-rings are very tight and the connecting rod seats nicely in its bearing. I had taken them all apart and checked the clearance.

Maybe I’ll squirt some soapy water into the space between the test tube and the cylinder to see if any bubbles show up when I rotate the flywheel.

Harry

 

[Harry Mueller]

I’m giving this a rest for a while until inspiration may again strike. I can’t really imagine why it stopped running completely after I “improved” much of the engine.

Here is a short video that I took when it was running for up to 30 seconds before quitting.

 

[minh-thanh]

Harry Mueller !
When the engine just stops, turn the flywheel and see if it is still moving smoothly ??
Try the cast iron piston
Below is a table for using materials for piston and cylinder. It's not mine, The poster is a member of this forum, I don't remember the link, I'm sorry !!

Your engine runs very well, find the cause .....
Hope you do better !

 

[Harry Mueller]

Thank-you, that’s very interesting and informative. It looks like my piston/cylinder combination is bad. I cant seem to do anything right. LOL!

Right now I’m trying to understand the theory of how these engines work because my motor runs in the opposite direction that I think it should run. Some call the stage where the hot air enters the power piston the power stroke while others suggest it’s when the cylinder cools and atmospheric pressure causes the power stroke. I’ve got to figure out which is right.

Harry