View Full Version : stirling engine won't run

04-13-2006, 08:54 PM
I just built the horizontal stirling engine from Terry Coss in the november/december homeshop machinist. And then used jerry howells site to tune it and get the arms going in the right direction. I can't for the life of me get this thing to run. I've doubled checked and rechecked the my parts and its all the same other than the fly wheel being made from aluminum. It doesn't even try to start. I used a small blow torch and then a bigger one and no luck. Can anyone give me some pointers.

Heres some pics.

04-13-2006, 08:59 PM
It certainly is pretty enough to run. Low friction is all important in those engines. If any of the fits are such that the friction is even slightly excessive that will stop it.

04-13-2006, 09:11 PM
well it seems to have very good compression and no air leaks. Also it seems to have very little to no friction. What about oiling the cylinders? Also how hot should i get it? I'm using a small blowtorch.

I can take a short video of how it acts if anyone wants me to. Thanks for you quick reply.

04-13-2006, 09:12 PM
With more reading than building and only a single 1.5" (height, not cylinder) engine under my belt, here's my $0.01

As Evan mentioned, all fits have to be precise and without drag. If you have only very slight drag, you may want to operate it for a "break in" period using an external motor (drill, lathe, etc.). This works wonders on metal to metal fits, won't do much on ball bearings. Use plenty of light oil on any metal to metal that's targeted for the "break in".

The graphite (glass??) piston must be especially low friction.

One last thing is to be sure that the phase of the two cranks are correct. I seem to recall the article lacking in some details. Any site with Stirling basics can probably help with the proper angles between the strokes of the two cylinders.

That is a nice looking engine and I may tackle it some day :)

added - most of the small to medium size Stirlings I've seen running live were running on small to medium alcohol lamps and turning pretty fast. One was the large fan from Jerry Howell's plans.


04-13-2006, 09:49 PM
I assume you're encouraging it by turning it over by hand as you're heating it. And trying both directions -- it may end up running opposite to what you expect.

The other guys otherwise summed it up pretty well. As Evan said, low friction is all-important. If you can somehow temporarily remove compression, it should coast freely, with little tendency to stop.

04-13-2006, 10:08 PM
well its got really good compression and when turing by hand, it has so much that when i give a quick turn it only goes about half a rotation. I just checked to see about any friction that may cuase a problem and didn't find any. even with good compression should it spin more easy than that. can it have to much compression. thanks

04-13-2006, 10:21 PM
Tronica, Like I said, not much experience here but a few more ideas :)

The compression you feel is very good but brings up another question. Is the timing of the motion between the power pistion and the displacer correct and is there a clear path between the cylinders?

Here's one simple animation that shows the relative motion between the two:


04-13-2006, 10:33 PM
There is a clean path between the two cylinders, and I have the displacer pistion 1/4 crankshaft rotation ahead of the power piston. I followed this guide from here,http://www.jerry-howell.com/Problems.html He says there should be no oil on the power piston?

George Hodge
04-13-2006, 10:57 PM
I made one of the 'Moriya' engines,but horizontal.It takes a lot of heat to get it going,but when it does decide to run it hums !! I've used two propane torches to heat it occasionally.After it's running,one will keep it going.

04-14-2006, 12:05 AM
like Evan says its likely a friction issue. These engines are have very little power, the tiniest different in the balance between a good seal and too much friction, and its a no go. is the liner ferrous? of so I would lap the bore and then finish turn the piston to fit.

I had a similar problem with a hot air engine. popular advise at the time was that the length of the fit between piston and cylinder wall contributed to the seal (which is true) however the only thing i could think of was that this was creating too much drag and to remove it would require a sloppy fit. instead i lapped the cylinder.... here's how i do it....

with a bore now smooth, straight and round (not something to take for granted when you're shooting for a fine fit) it was time to work on the piston. Intuitive engineering said to me that the seal is a function of the length and clearance between where the piston contacts the cylinder. With a perfectly round cylinder, I thought that having a very close toleranced fit over a small distance would maintain the compression while reducing the drag. That was the backyard engineering theory, and it seemed to work

I took a flat piece of bearing bronze and turn two rings. I turned two shoulders on the piston and shrunk the rings on. holding the piston on a mandrel, I finished turned the rings in situ to the closest tolerances i could, and presto the engine ran like a dream on very little heat!

oh yeah, do use some light oil in running


gratuitous shot of the engine - reflection gives a sense of the bore's finish


Mad Scientist
04-14-2006, 01:31 AM
As mentioned before any undue friction is a real killer for a small engine. Beyond that:
Are the cranks for the power piston and the displacer positioned so they are 90 degree apart?
(Once running this 90-degree can be tweaked for maximum efficiency.)
Is the diameter of the displacer slightly less then the diameter of displacer bore? (Can air easily flow between the displacers outside diameter and the inside diameter of the displacer bore.)
Are you heating “just” the bronze hot end, the cold aluminum end wants to be as cold as possible?
You might want to consider some sort thermal insulator between the bronze and the cold aluminum end.

[To err is human to blame it on someone else shows management potential.]

04-14-2006, 10:57 AM
Wow, McGyver, that's a beautiful R-E; great photography, too.

Here's a good way to test for excessive friction: Flip the flywheel against compression and quickly release your hold on it. The flywheel should bounce back. Even better, it should bounce back and forth a few times.

If the engine doesn't bounce back, readily, from compression, there is either too much friction or there are excessive air leaks, or both.

The Stirling engine on this Web page has only a 3/8" diameter power piston and a 1/2" displacer. Yet when flipped against compression it bounces back and forth several times.


Good luck,


04-14-2006, 11:10 AM
Here's one more thing that should be checked: The displacer for air-tightness.

To check the displacer for leaks, remove it from the engine, but leave it on its operating rod. Then, plunge it into a pan of boiling-hot water. If a stream of bubbles start coming out of it, the displacer has an air leak and must be repaired before the engine will run.



04-14-2006, 01:08 PM
With the power piston at TDC, heat the hot cap and watch the connecting rod
carefully. If you have good seals, the rod should move outwards as the air

Check for friction free motion of the displacer in its chamber. Even if all
seals are perfect, a rubbing displacer can create enough friction to stall the

A propane torch should not be needed at all. My buddy just got done building
one of these and, now that we've tuned it, it runs nicely on an alcohol lamp.
(Alcohol generates a very hot flame.) Massive amounts of heat from a torch
can raise the temperature of the cold end of the chamber. The engine's
efficiency is a function of the temperature difference between hot and cold

What material was used for the hot cap? From the photos it looks like brass or
bronze. A highly conductive hot cap material will conduct too much heat to the
cold end and nullify the temperature differential.

If all else fails, consider building a new hot cap from stainless or carbon

04-14-2006, 01:47 PM
I'm with nheng wondering about timing, and how the two cylinders are connected.....Is there a passage between the two in the aluminum mounting plate?, and what size is it?....If it's too small in relation to the air volume being moved that could keep it from running.....


04-14-2006, 02:45 PM
Hi Tronica.

You finished yours quick and it looks good. Good Job!

Looks like you deviated from the plans a little. I noticed your flywheel has more mass than the plans specify. You would think once in motion it wouldn't matter but it may due to friction at the bearings. For efficient energy storage in a flywheel you want most of the mass to be fatherest from the center. Your flywheel is probably not doing much for you.

Also, did you use a stainless shim between the hot & cold end? I think that is very important and especially true in our case because we are using brass hot ends.

Also, I used stainless hold down bolts for the hot/cold end.

I would expect you would not have to supply too much heat to get things moving because the brass host end, although not the best choice, does have the advantage in that it should heat up fast.

You got me nervous and anxious to get mine done. I should have it done in two more weeks because is only have a partial weekend day to work on it.

I wouldn't worry. Once you find the problem it will probably run like a top!

Keep us posted!

04-15-2006, 11:13 AM
the arms, are 90 degrees apart. The end cap is made of brass. there is a passage way between the to pistons, cant remember the size at the moment. i will check for air tightness.

04-17-2006, 04:51 PM
How's it going? Have you had any luck?

I finished the power piston rod, bushing and displacer connecting rod. I'm using a solid 3/16 rod into the displacer so I didn't have to turn down that connecting rod.

04-17-2006, 11:01 PM
I built this engine and after a little fine tuning it ran. First, the displacer and power pistons should be phased 90°. Next, what I thought was a little friction turned out to be too much. I lapped the power cylinder untill the piston would free fall in the cylinder with the intake port open. With these corrections I placed the power piston at TDC, applied heat to the hot end and noted a very slight movement of the connector rod.
I removed the dust seals on the bearings, degreased them and lubed them with an oil of low viscosity (Marvel Oil). I also oiled the Power Piston and the dispacer rod with the same oil. My hot end was made from stainless steel. I use an alcohol lamp for heat. It takes a couple of minutes to reach operating temperature.
The engine will run only in one direction depending on the direction of the 90° phase. The flywheel will spin easier in the Run Direction.

This is about all I can offer. Fortunately, I had a friend who was "Stirling Literate" and I was able to get some pointers from him. I am not SL, but to me this engine is a lot less sensitive to friction than I expected.

I hope this helps and keep us posted.
Paul C

04-17-2006, 11:45 PM
Paul, You just brought up an interesting point. If bearings with SEALS are used instead of bearings with SHIELDS, the increase in drag is considerable. This holds true regardless of bearing size.

The solution (temporary) is as you say, pull off the seals, get the grease out and re-lube the bearings with light oil.

Gotta remember that when I go to get bearings for a Stirling in the future :)

04-18-2006, 12:10 AM
You have my sympathy.
After spending a many hours in the construction of another HSM project, Crusader .60 I find, as noted the last issue of HMS, if the engine was built to print, it will never run!!!
I hope you are not presented with the same.
It seems that an error in writing or printing could exist any ware in your project and HSM might or might not find and publish the correction.
With any luck maybe someone who has built the sterling will see your posting and give you the correction to allow your project to function.

Good luck

04-18-2006, 12:40 PM
sorry i havn't posted in awhile. but i tried oiling the both pistons went through the whole engine for friction and got this thing as good as i could. still does not run. i heated it up beyond what it needed and also used a drill with a rubber wheel to get it spinning a still nothing. i might remove the seals from the bearings and try removing the grease and just using oil.

04-18-2006, 12:57 PM
You have my sympathy.
After spending a many hours in the construction of another HSM project, Crusader .60 I find, as noted the last issue of HMS, if the engine was built to print, it will never run!!!
I hope you are not presented with the same.
It seems that an error in writing or printing could exist any ware in your project and HSM might or might not find and publish the correction.
With any luck maybe someone who has built the sterling will see your posting and give you the correction to allow your project to function.

Good luck

Are talking about the engine i'm building or the Crusader .60 has an error in the plans. What is the problem you found in either one. I noticed that article i used for this had many things that didn't make sense

also i found an post by mklotz that he used gas pipe for the cap and was wondering what he was referring to. could i just use steel for the cap?

04-18-2006, 01:56 PM
i might remove the seals from the bearings and try removing the grease and just using oil.
Ok, that is a good place to start. Don't confuse smooth turning with low friction. Grease in the bearings is a show stopper. I built a little air/steam engine with the express objective of making one that would run on the lowest possible air pressure. I used ball bearings with no seals or covers and rinsed them out with solvent. The ball bearings should spin freely with a touch of a finger. After that I lubricated everything with clock oil which is an extremely thin oil designed for minimum drag. Anything heavier is much too thick. I was able to get the engine running at 600 rpm on less than .5 psi air but only by reducing the friction to tiny amounts at every possible point.

04-19-2006, 03:28 PM

After you cleaned the bearings of grease, how far did the piston move on it's own when you applied heat to the hot end?

Do you have any pictures?


04-19-2006, 04:12 PM
i havn't tried the bearings yet, havn't much time. i will try that later today and get back as soon as possible. Thanks to everybody who has given me pointers.

oh i will take pics.

04-19-2006, 07:15 PM
ok i tried removing the bearings seals and used light weight oil, and i i ithink helped a bit. however the engine stills feels tight. I'm not sure where to go from here. this project may be put on the back burner soon. also can anyone tell me about using steel for the cap, will that be better that brass.

04-20-2006, 11:16 AM
If a hot air engine feels tight it will not run, period.

Keep working on finding the cause of the tightness. The "bounce-against-compression" test is the easiest way to check for excessive tightness.

I have hot air engines that have brass, steel and stainless steel hot caps. The stainless steel works the best of all.

Your choice of hot cap material, however, is not the cause of the engine not running.

Did you put some sort of insulating gasket between the hot cap and the rest of the engine? Every means possible should be used to minimize heat conduction from the hot cap to the rest of the engine.

If the rest of the engine heats up right along with the hot cap, it will not run.


04-20-2006, 06:24 PM
well after a whole two days of messing with it, it still won't run here what i've done:

went through the engine checking for friction
took the seals of the bearings and replaced the grease with oil
checked for air leaks
polished both pistions
polished both cylinders
i do have a gasket between the cap and the cylinder and a spacer

i've done everything i can come up with. i'm thinking this engine wasn't ment to be run.

04-20-2006, 08:51 PM
I feel you pain, everyone's had projects that didn't work and its frustrating. sometimes a fresh set of eyes or bit of experience can be whats needed. i don't know where you are, but if its urban maybe there's some model engineering clubs nearby?

04-20-2006, 10:04 PM
the plans say that the displacer piston has .072 clearence between the cylinder wall. is that right, mines less, .010 to .012. not sure if that matters

04-20-2006, 10:30 PM
One thing that can make engines or other small mechanical assemblies "tight" and is not obvious is when a pin, such as a crank pin, or similar rotating part, is not perfectly perpendicular as it should be to a driving plate or other mating part.

Upon rotation,the part that is not perpendicular will do a really good job of binding up over a repeatable range of rotation.

Don't know if this may apply with this engine as I've been too busy to go back and look at it yet :( Den

04-21-2006, 11:34 AM
Quote: "the plans say that the displacer piston has .072 clearence between the cylinder wall. is that right, mines less, .010 to .012. not sure if that matters."

That little clearance will certainly have a damping effect on the engine. I recently finished a hot air engine that has a 0.500" dia. displacer. The clearance on it is 0.015". Larger engines should have correspondingly larger clearances.

For one thing, on a horizontal engine a vert small clearance will usually mean the displacer will rub on the hot cap.


04-21-2006, 02:59 PM
It may be a combination of the displacer clearance, flywheel weight and not having a stainless shim between the hot and cold end.

The air has to go past the displacer within a certain time frame and stored energy in the flywheel helps it through this transition. I would stick to the plans as close as possible because there may be an optimal combination of flywheel weight and displacer clearance.

Not having a shim is just hurting your heat differential and your power.

As for my engine, I need to build my hot end and the displacer piston and I'm done. After reading all the posts I'm really doubting mine will run without some rework.

04-21-2006, 03:33 PM
I've made a aluminium and a steel flywheel. the steal one might be to heavy. I don't have a rotary table so i don't have good way of removing some of the center of the flywheel. can you suggest anything. also kndroy can you post some pics of yours.

also i just used a plain steel shim, is that good enough? Thanks for the help guys.

04-21-2006, 05:52 PM

I'd use the steel one. Flywheels store energy by either velocity or off center mass. These engines don't rotate very fast so you need the mass. The mass at the center contributes less to energy storage and just adds more load on the bearings.

If you don't have a lathe or a rotary table I would get a hole saw and cut 4 or five large, equadistant circles in the middle so the mass is located mostly on the radius. The danger there is throwing the flywheel out of balance.

I was thinking more about the flywheel and I think it plays more of a role than I originally thought. For single cylinder engines the stored energy gets your crank past TDC and BDC. In a Stirling the displacer is in the middle when the power piston is at TDC or BDC and pushing air across the displacer. The flywheel must supply energy to this as well. The trade off is you have to produce extra energy during the power phases of the piston to be stored in the flywheel. If you are missing components like the stainless shim you might not be storing enough energy to get through TDC and BDC.

I'm certain the steel shim is doing nothing to help you. You would be better of using some sort of material that doesn't conduct heat.

Also, the holes for the four hold down bolts on the displacer cylinder are drilled oversized so heat from the bolts can dissipate into the air instead of the cylinder wall on the cold end. This is important if you used steel bolts.

Lots of subtle little design details that were not explained in the plans.

I'll get some new pictures up tonight.

04-22-2006, 08:38 PM
kndroy hows your stirling engine coming. I'm curious to see how it performs, and what yours looks like.

04-22-2006, 11:56 PM
Hi Tronica.

I finished the displacer piston last night and all that is left is the hot end. I'm thinking about using aluminum for the hot end because it is easy to machine and I can't find any brass at the metal supply. Aluminum can't be much worse than brass.

I made the base thicker than the plans specify. I made it thick enough so the engine can rest on it's base and the flywheel will spin. I put some clear rubber feet on the bottom so it will not slide.

I'm worried because the displacer sits in the cylinder a little crooked so I hope it clears when I get the hot end on.

Here are some pictures...



04-23-2006, 12:09 PM
kndroy its coming along nicely. I"m curious to see how the aluminum end cap performs.

04-25-2006, 02:58 PM
finally got it running, will post pics later.:D

04-25-2006, 06:04 PM

What did you have to do?

More Pictures!

Ataboy sticking with it! Good Job.

04-25-2006, 09:06 PM
i gave the displacer piston more clearence, i didn't have a drill bit long enough to go from one cylinder to another for the airpassage, so i drill from both ends. It turned out it was leaking air from around the threads of the rod guide into the displacer cylinder. i got it to run on a small alcohol burner, but only about 100 rpm. so i used an antique blowtorch to heat it. (small one, 1/2 inch flame.)

I dont' have the camera today, but tomorow i will get some up. I extremely curious about your aluminum end cap.

i will also try to make a short video of it going.

05-01-2006, 03:01 AM
I finished it up this weekend. It didn't run at first but I tightened up rod guide and it fired up with a Butane torch. I think something is wrong because it takes quite a bit of heat to get the thing going and to maintain it. Part of the problem could be the aluminum hot end.

Here's the final pictures.



I took a video but I need to get it off the tape and upload it.

Thanks for the help.

05-01-2006, 10:29 AM
You definitely do *not* want an aluminum hot end. Aluminum conducts heat rapidly toward the cold end. Stainless steel is the best material for the hot end. Second choice would be ordinary mild steel.

Good luck!


05-02-2006, 11:38 PM
Kndroy, you asked how much travel did I get when I applied heat to the Hot End. Very little, like 1/8" and that was with a propane torch which is more heat than you want or need. I would not use this as a test procedure on this engine.
There are several build features ( my engine ) I want to pass along. For the heat resistant material specified between the Hot Cap and the Cold End, PN 8, I used 1/16" thick teflon. I am sure that the intent is to minimize heat transfer at this junction. I ordered the Teflon from McMaster Carr, PN 8545K13. I would not reccomend metal; you want a insullator.

I barely clamp the ABEC-7 Bearing in the Pillow Block. If I clamp the bearings snug, there is a noticable diference in drag.

I need a fast spin to start my engine. It won't run slow. It runs at a unique speed that I think is a function of the heating-cooling rate. Over time the Cold End will heat up and the engine will slow and stop.

As you may recall, my Hot End is made of Stainless Steel. It takes a long 3-5 minutes to get to Run Temperature. I made an Alcohol lamp and I also purchased a Dual Wickless Alcohol Lamp from HomeScienceTools.com There is a substantial diference in engine start times between these two lamps.The Dual Wickless will start the engine quicker (on the 3 minute side).

I hope this information is usefull. I want to quantify some of the measures I mentioned above like how fast my engine runs and for how long will it run. Maybe we can compare notes. I have no idea of what to expect in performance.

05-03-2006, 03:54 PM
Thanks for the tips Paul.

I'm going to check the pillow blocks and make sure they are not too snug.

I used stainless shims between the hot and cold side and a Aluminum hot end. I think things are working well now that the engine is broke-in. It takes a minute with the Map-Gas to get it up to temp but it really starts moving. I would say it gets up to two or three hundred RPM with intense heat.

Here are some of my observations:

-There is a certain point to where more heat does nothing and at that point I pull the flame further away from the engine. At that point the engine really gets going. There is a 'sweet spot' as far as temperature.

-The cold side stays just warm while it is running while the hot end is getting blasted with a Map-Gas torch. You can leave your finger on the cold side the whole time. When the engine stops the cold side gets hot. This tells me the heat is not traveling over to the cold end and there is a good heat differential.

-If I get it up to temp before I spin it, it requires very little spin to get it going.

-I've noticed I have allot of play in the displacer rod bushing and it doesn't seem to affect the engine.

-Once it starts spinning it will accelerate up to full speed.

-I oiled piston only during break-in now I don't use any oil. A little oil remains but I wipe it off and I'm not adding anymore.

-I left the engine running for ten minutes and it ran perfect the whole time. No of slow down observed.


All in all, my biggest question is why should we keep the heat down? I blast mine until there is no additional RPM increase then I back off. I can't imagine an Alcohol lamp could supply that engine with enough heat to get it up to full speed. Should I see better results with less heat? I would like to use the lamp so I can run it inside the house.

I have a video of it running. Do you know a website where I can upload it to?

I'm going to get one of those Alcohol lamps and try it out. I bet if you used a more intense heat source it would heat up faster and RPMs would go up.

05-03-2006, 09:06 PM
Kndroy, try video.google.com


just click the apply button at the bottom. I too will have a vid up soon.

John R
12-16-2007, 07:43 PM
I have just started on the engine by Terry Coss as shown in the Nov/Dec 2005 issue and read all your posts.I noticed in the artical that he said not to sand or buff the cold end cylinder but it sure looks polished to me. Is that a misprint or am I missing something?
What about maching the OD of the cold end ... did you guys mount it on a mandrel ?
John R

12-16-2007, 07:53 PM
Hi tronica,

you have had the answers from other people so what I can offer is only my best wishes.

Hi Evan,

"It certainly is pretty enough to run" you say.
My wife 35 years ago was pretty enough, but didn't run so I ended up married...


01-02-2008, 04:22 PM
John, I sanded the outside of the coldend, to me the inside doesn't matter if its not ruff. Because theres clearance around the cylinder, same with the hot end, the piston does not touch any part of it. I didn't have a big mandrel to mount it, so made a cap for each end, with a good fit for each end, i mounted it on a smaller mandrel. The other end i used my live center against the cap. Then i turned the fins, and sanded. And took the caps off. If needed i can post pictures of the caps.

John R
01-03-2008, 09:51 AM
I ended up making a mandrel for the cold end. Came out fine
John R