Working On A LMS Stirling Kit Build

[George_Race]

I have been encouraged since my first little rocker engine ran the first time I tried it. See here:http://www.homemodelenginemachinist.com/index.php?topic=14528.0

About a year ago I purchased a couple of material kits from The Little Machine Shop. Both are Stirling Engines. I must admit that when they arrived I was overwhelmed with the complexity of the machining needed to build them from the raw materials. They have been sitting on the shelf for some time. As a novice hobby machinist, my first build was a little rocker engine, and it ran the very first time I put air to it. That and all of your kind comments encouraged me to bring down one of the Stirling material kits from the shelf. After spending a lot of time going over the pages of prints and pictures, I decided to start the build. Having all the prints in Metric was my first challenge. I learned how to do the conversion to Imperial and that seemed to help a lot. In the mean time I ordered several measuring tools that are Metric as well.

The picture below shows some of the first pieces that I finished off. I first did the base plate on my home brew CNC. Using CamBam I drew and compiled the G-Code to face off the surface of the aluminum plate. After several passes, a thousands or two at a time, I think it came out really looking nice and it is smooth as a piece of glass! I really like the "tooling" finish my mill leave behind.

I then faced off the flywheel and drive pulley mounting block the same way, using the CNC to true up all the edges and surfaces. The drive shaft and bushings were next. Then the drive pulley and flywheel. One piece at a time I am turning chunks of aluminum into finished parts. This is a really neat hobby, and I am really learning a lot by trial and error as I move ahead.

Next I managed to get all the parts of the flywheel assembly to fit together and spin very smoothly in it's mount. I must admit that I had to make three drive shafts to get everything the right size to fit together. There must be a simple way of turning a piece of brass to "press fit size" the first time! It seems like every time I try I end up taking one last pass too many, the the fit is too loose. Oh well, hopefully my skills will improve with time.
Here is a picture of the drive shaft and wheels all together on the base plate. Along with it is the aluminum block that holds the hot and cold cylinders in place. I think that has really come out very nice as well. Again I love the machining finish left behind by the CNC. It is finished expect for drilling the air passage the long way thru the block holding the cylinders. Have a long drill coming, and that hole is my next challenge.

The next picture shows the two cylinders in place on their mounting block. I kind of feel like it is cheating a bit on the build, having the cylinders and pistons the only parts that came in the kit that were finished. As those are probably the most critical parts for the engine to work properly, I guess I am comfortable with this my first Stirling build, to not need to worry about building those individual parts.

The big round chunk of aluminum on the left is the finished cooling heat sink for the hot side of the engine. I used the CNC to bore the hole in the center and it is a beautiful fit to the hot cylinder. I pushed it on, left it on the bench over night, and the next day I could not remove it. I sat it on a window ledge in the sun and in about an hours time I was able to slide it back off the cylinder. Boy, to me that is a perfect fit. Guess I got really lucky on that one.

The next pictures shows some more progress. I cut the cooling fins into the cooling heat sink. I call it my "need to plan ahead" piece! As you can see, two of the fins are considerable thinner than the rest! Should have done a bit better on the planning, BEFORE I started turning the piece! Other than the looks, I guess it really will not matter when all is said and done.

In the foreground is the alcohol burner. Two more chunks of raw aluminum turned into a finished piece. One thing about all of this so far, I have put more time on my lathe with this project, than I have in the two years I have owned it. Hopefully my skills are improving with each piece I turn out!

The next picture shows the finished heat sink slipped on the hot cylinder. Let it set over night again, and it is firmly attached, all by itself! Looks like all I have left to do is build up the connecting rod assemblies, get all the parts assembled together, and then fire it up! At the rate I am going probably a couple of more weeks and I will see if it runs. Will add more pictures and comments as I progress.

 

[mklotz]

George, it looks as if you're making excellent progress and learning a bit as you go. Good for you. It's a brave man who makes the leap to a Stirling as his second project.

Making the fins "come out" perfectly does indeed take a bit of planning. Here's the technique I use...

n = number of fins
w = width of fin
L = length of workpiece
n-1 = number of inter-fin slots
s = slot width

Now, it must be true that the total fin width and the total slot width must add to the length of the workpiece, which yields the following equation:

n*w + (n-1)*s = L

so, solving for s, we have:

s = (L - n*w)/(n-1)

If, after solving for 's', you find it's smaller than your cutoff tool width, you have two options. The first is to grind a smaller tool. Alternatively, if the engine design permits, reduce 'n' until the calculated 's' is >= the cutoff tool width. Or, if the fin width is not critical, you can reduce w until the condition is satisfied.

I have one other comment. You wrote:

"Along with it is the aluminum block that holds the hot and cold cylinders in place."

Stirlings of the type you're building do not have separate hot and cold cylinders. The cylinder with the cooling fins is called the displacer chamber. In operation it's kept hot at one end (by the flame) and cool at the other end (by the cooling fins). The air inside is pushed back and forth by the displacer and alternately heats and expands then cools and contracts. The other cylinder in your engine is the power cylinder. Inside it, the expanding air pushes on the piston to power the engine.

Good luck with your engine. We're looking forward to its completion. Let us know if you encounter any problems of have any questions.

 

[b.lindsey]

Thats a lot of progress you have made there George. The fins don't really look bad at all, but it it bugs you, you can always remake that piece using Marv's advice. As for the power cylinder (with the square flange), did it come that way in the kit or did you have to fabricate it by joining two pieces?

Keep up the nice work!!

Bill

 

[George_Race]

Marv, thanks for the explanation of the proper terminology, someday I will become accustom to all the "buzz" words that go along with this hobby. In the mean time I do appreciate folks like you on this site that drag me along, learning as I go.

I like your approach to the fin spacing. I may do the heat sink over some time if I can find an appropriate piece of scrap at my local metal shop. I have both 1/8 and 1/16 parting tools. I have the one's with the "T" shaped top, they do seem to work really well.

Bill, to answer you question about the flange and cylinder. The LMS kit comes with both cylinders finished and attached to the brass mounting flange. They both also contain the fitted pistons as well. I guess they figure those parts are more difficult to make, especially for us first time builders. Everything else is just raw material that needs to be turned and milled to size. I had trouble at first reading the Metric prints, terminology that I had never seen before. I dropped LMS an email asking questions about some of the notations on the prints. They emailed me back a nice sheet of information explaining all the Metric terms and symbols used in the drawings. Boy, did that ever help me a lot.

George

 

[mklotz]

George,

A little preemptory advice...

When you get around to fitting the "pistons" to the cylinders you'll find that the power piston is probably a nice snug fit in the power cylinder. That's as it should be. However the other "piston" (its proper name is the displacer) will be a loose fit in the displacer chamber. That's as it should be too. The displacer is merely a "pusher" whose role it is to move the air back and forth between the hot end and the cold end. As such there must be some clearance between the displacer and the displacer chamber walls so the air can flow around the displacer as it moves to and fro.

 

[George_Race]

I'm back! Finished the little Stirling today and now I need help and advice.
It looked so easy and I was expecting it to run when finished. Well guess what, it will not do anything except sit there and soak up the heat from the burner.

It really spins over very nice, no binding anywhere. I was told to time it so that the power piston was 90 degrees ahead of the displacer piston. In the pictures you can see the connecting rod is at the bottom of the drive wheel, and on the flywheel side, the power piston connecting rod is 90 degrees ahead. It turns counter clockwise as you look at it from the drive wheel side.

My starting instruction were to apply heat for one minute, then spin it over by the flywheel and it should keep turning on it's own. I spin it over and it goes around 10 or 15 times and then just slows and stops. Does not seem to spin any more with heat applied than when the whole thing is just setting there cold.

I have a good fit on the power piston, if I remove the the displacer assembly, put my finger over the hole in the block, the power piston creates both pressure and suction on the in and out stroke when turning the flywheel.

Nothing seems to be rubbing or binding anywhere, I am lost as to what to do next.
Pictures follow.

 

[deverett]

George

No doubt you will get lots of advice from members here, but one place you could try for possible solutions is Jerry Howells page 'Why won't my Stirling engine run?'

http://www.jerry-howell.com/Problems.html

Dave
The emerald Isle

 

[b.lindsey]

George,
As I look at the pictures and your description, it seems to me that the power piston is lagging the displacer by 90 degrees. That assumes that what you are calling the drive wheel is the crank disk that drives the displacer and that rotation is CCW when viewed from that side of the engine. Maybe I am misreading but that's what i see.

Bil

 

[mklotz]

When the engine is hot, does the displacer move freely through its cycle without any dragging against the inside of the displacer chamber?

Do you have a good seal where the displacer rod enters the displacer chamber? Try adding a drop or two of heavyish oil at this point to form a better, though temporary, seal and see if that improves things.

What are you using for fuel in the burner?

As an experiment, when it's making its "10 or 15" revolutions, drip some cool water on the fins and see if that extends the length of the run.

You may have an air leak somewhere. Immersing it in water can isolate those but, before you do that, report on the things mentioned above and let's see if we can puzzle it out.

 

[George_Race]

I am sure the displacer moves freely, hot or cold, and does not rub inside of the chamber. I unhooked the power piston and removed the piston, the displacer now really spins freely. I tired the drop of heavy oil on the displacer rod, no change and I could see the oil on the rod and covering the opening at the outside end of the displacer rod bearing. The timing is at 90 degrees with the power piston leading the displacer by 90 degrees. I am burning denatured alcohol in the burner. The displacer really get hot quickly, as does the heat sink, although the heat sink is never so hot you can't hold on to it with your fingers. The only thing, being suggested, that I have not tried is the cold water drops on the heat sink.

This is discouraging, but at least I had a great time machining the parts and learning how to better use my lathe and CNC. Maybe I better stick to air driven ones, at least the first one I built runs just great. Or maybe, I should try some kind of a IC engine, although I don't think I am ready to hold the kind of tolerances needed to get one running. Decisions, decisions, and this is just a hobby!

Does anyone have any other advice or things that i should try?
George

 

[mklotz]

Are you *certain* that there is no obstruction in the air passage leading from the displacer chamber to the power cylinder?

You should still check for air leaks. Make up some soapy water and use a brush to apply it to the various joints while turning the engine over by hand (no burner).

Be patient. The engine is a tested design so you're fortunate in that you're not fighting design problems. Keep trying different things. It will eventually work and you'll be over the moon.

 

[arnoldb]

Hi George

I could not help but notice from the fist picture in the last set you posted that it looks like the hole going from the outside to the power piston looks like it's not plugged...
I could be wrong though.

Hope you get it going soon Thm:

Kind regards, Arnold

 

[fcheslop]

Hi George
I would follow Marv's advice as the usual culprit if everything is built correctly are air leaks and I know this design works from the drawings.What did you use to seal the cylinders to the block
best of luck Frazer

 

[George_Race]

Thanks for all the help guys, still struggling on this end.
Arnold, the hole in the first picture is plugged. Threaded the hole and screwed in a short screw with thread sealant on it.

Now Frazer, that is a very good question. I milled the openings in the block so that the machined ring on the back pact of the cylinders fit it exactly, it is about .010 thick. Do you think that I need to seal them even better?

If I remove the displacer cylinder and piston, put my finger over the opening and then push the power piston in and out holding on to the connecting rod, I get a lot of pressure to overcome when going in, and it has a lot of suction when pulling out. So much suction it will pull about half way back in if I try to withdraw it and let it go as I reach the outer limit with the piston.

Today I went through the timing again, and the power piston is definitely leading the displacer piston by 90 degrees. There is definitely some gain in the free spinning with heat applied. My guess is that it makes at least one more rev maybe even two more with heat applied than it does just sitting there cold when I spin the flywheel.

When the heat sink started to feel warm I ran some cold water over the fins, nothing changed. i then slipped the cooling fins off, and applied a cold wet rag directly to the back of the cylinder, against the block. Nothing changed.

I am about at the point where if I could get back what I have invested in the kit I would let it go! I never dreamed this would be so difficult. There has got to be some simple thing that I must be missing somewhere.

Any further things I should try?
George

 

[b.lindsey]

George, the next thing i would try would be adjusting the timing maybe as much as 15-20 degrees ahead of or behind the "correct" 90 degree setting recommended.See if doing that makes any difference in revs with or without heat applied. It could be a clue and even if not, you will have eliminated another variable.

Bill

 

[fcheslop]

Hi George,as already suggested mix some soapy water and check for air leaks when she eventually runs the grin will go from ear to ear but don't worry that the wife wont understand :big:
best of luck Frazer

 

[techonehundred]

When I was having trouble getting a Moriya stirling to run, here is what I did. Take that screw out of the threaded hole. make an air fitting to connect to it. Do not put much air on it, no more than 10 psi. Put it in a container of water. You will be amazed where the air is leaking out. once you see, get some form a gasket and seal up the areas that are leaking. Even areas that you thing are really flat and smooth tend to leak air. once it is sealed, and the threaded hole plugged, you should feel a slight compression when you turn it over. I worked on one for about three months and was just too pig headed to believe it was leaking. Once I got it sealed, It amazed me how it would run.

 

[winklmj]

DO NOT GIVE UP. Read this site for the trials and tribulations many have gone thru to get an engine running. If anything, just set it aside for a while and come back to it later. But I encourage you to keep at it. With the expert help here it WILL run.