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Stirling engines

Stirling Silver II (single cylinder Beta engine)

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Raymond Griffin17/01/2010 19:31:50
53 forum posts
38 photos

I have recently completed the replica Stirling Silver II (single cylinder Beta engine) following plans in the book Stirling and Hot air Engines by Roy Darlington and Keith Strong. It will not run and is very frustrating as I feel that the engine is well constructed, has good compression and is as friction free as I can make it.

When I heat the hot cap, the internal pressure builds until it is difficult to turn the engine over against the compression, so no worry about leaks.

The purpose of this note is to ask if anyone can give any helpful comment on getting it going. Particularly if they have made this engine.

I would be extremely grateful for any comment.

Ray Griffin

Mark Smith 318/01/2010 04:41:07
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In my experience, such as it is, besides leaks and friction, timing is another big factor. Some engines are happy at 90 degrees and others somewhat either side of that magic number. Also I have found that a minimal clearance of the displacer from the top of the hot cap is very critical. Are you able to alter the timing? Oh, I have just looked at the plans and I see it is a bell crank rocker driving the displacer, very difficult to alter as it is driven off the main crank. I tend to use offset cranks that are easily changed to advance or retard the timing.  My latest engine the "Devon" was a difficult engine to get going but after a lot of adjustments to the cylinder position and the timing it went and now starts after a short warm up with one flick. On the Stirling II there appears to be some adjustment on the displacer tube as the big end screws into the tube. You could try adjusting that until the displacer just touches the top of the hot cap and back off to just clear. Hope this helps.
Mark 

Edited By Mark Smith 3 on 18/01/2010 05:20:36

Ian S C18/01/2010 07:19:43
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7468 forum posts
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The way I set the adjustment of the displacer is to put a bit of cardboard or similar of the correct thickness in the end and adjust to that,making sure at the same time I have clearance at the cold end.None of my engines have enough compression that it becomes difficult to turn them over.Some have been a right B***** to get going the first time,but after the first run usually become easier and easier.I think I saw the engine you'r building when I flicked through Mark,s book.What is the displacer made of?If aluminium it may be best to allow a fraction more clearance than if it were steel or stainless which don't expand so much.Ian S C
DMB18/01/2010 10:24:28
1012 forum posts
Hi Raymond,
If advice given by others still not bring desired result, contact Roy himself. If you need it, I`ll give u his phone no., I`m sure he won`t mind, he`s a very amenable chap, known him for years as a fellow Worthing Club model engineer.
John.
Steve Bell 119/01/2010 16:41:34
5 forum posts
Hi Ray,
 
I've made a couple of hot air engines (a scale Robinson engine and a stove fan) and along with the usual reducing friction and leaks I've found aligning eveything to be critical.
 
On both my engines with almost zero clearance between the power cylinder and piston and between the displacer rod and bearing, getting everything in line/perpendicular was vital.
 
Could you try undoing the pivots and feeling the side play in the linkages to make sure that nothing is being pressed to one side?
 
Steve
 
Oh and the only other problem that the fan had when it wouldn't run, was my dad was trying to spin it the wrong way!
Ian S C20/01/2010 00:48:25
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7468 forum posts
230 photos
I don't know what you'v done as far as running the motor in by driving it either with a low speed motor or by hand,firstly if possible without compression,then for a short time with compression,at this stage a little heat may help if its hard to turn over.A the last stage of things you'll notice it frees up and if an electric motor is used,with an ammeter in line the current will drop and the revs increase.They can be bl***y frustrating,not the first time I'v ended up with a sore arm trying to start a motor the first time,but once you get it going it rapidly improoves.Ian S C
Ian S C20/01/2010 09:38:36
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You are turning it the right direction Ray?Ian S C
Raymond Griffin20/01/2010 19:15:32
53 forum posts
38 photos

Dear Mark, Ian SC, John and Steve,

Many thanks for your thoughts. I too have wondered about the timing, as Stirling engines that I have previously made were more sensitive to this than I imagined. The timing crank on this engine is less than 90 degrees and perhaps some alteration could help, though in which direction? Timing of Stirlings never seems to be what I think it should be. Having said that, I did find with my "Denney Improved Ericsson Hot air Engine" that the timing was right first go.

I will take up all your suggestions.

But first, I will telephone Roy as suggested by John. I will be in contact for his number John,  next week. How do we get in touch? I live in France and will be in the UK this weekend to go to the show at Alexandra Palace on Saturday. So will be in contact when I get home.

Cheers to all

Ray

Ian S C21/01/2010 01:37:32
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7468 forum posts
230 photos
When you'v contacted Roy,could you pass on his wisdom,it could help us all.Look among the hot air engines,you might find him at the show(its model engineering I suppose)Ian S C
Robert Hornby04/07/2010 04:37:21
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8 forum posts
13 photos
My question is not specifically on the topic above but I cannot seem to find how to start a new thread.
I would like to build a model stirling engine as depicted on the cover of MODEL ENGINEER dated 2-15 December 1998. I only have a photocopy of the front cover of the magazine. Is it possible to purchase the plans ( or the magazine it was published in - if it was published)?
Robert
John Olsen04/07/2010 06:51:14
1078 forum posts
91 photos
1 articles
Hi Robert,

Slight correction, that would be 2-15 December 1988, not 98. It often pays to quote volume and issue number as well as the date if you can. (vol 161 no 3838)

Anyway, the engine is a demonstration Stirling engine by Peter Meede in Germany. There is an article starting on page 699 of that issue, and concluding in part 2 in issue 3840 vol 162 dated 6-19 January 1989.
The second issue has the drawings, in metric. Looks quite buildable from the information given, although this is not a detailed construction series. The burner is a glass Pelikan ink bottle, which might be a bit hard to source these days. But I suspect any nice looking glass bottle of about the right size could be used.

I guess it is obvious that I have copies of the magazines, and could arrange copies, provided that does not offend any Editors who may be watching. However, I live in the Antipodes, so possibly somebody a bit closer may be able to come up with a copy for you. Many clubs have extensive collections of ME, some going back to issue 1. My own collection only goes back to the forties. (no I am not that old myself)

For those who are wondering, the engine looks very nice, a somewhat futuristic style in brass. I can see why it would attract as a project. I'm no expert on hot air engines, having built just one (Rider-Ericsson) but this certainly looks like reasonable project with no really tricky stuff involved.

regards
John
Terryd04/07/2010 07:03:59
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1935 forum posts
179 photos
Hi Robert,
 
Have you tried your local library, many libraries keep bound copies of Model Engineer.  My own library goes back to mid 1940's, bound as annual volumes.   Usually libraries are run by local authorities and have inter library loan facilities which will get the volumes for you for a very small fee.  Wonderful value!!
 
By the way John,  under copyright law in the UK one is allowed to copy a chapter, article or 5% of a book or publication when used for research or personal use.  Our purposes would be defined as that.
 
Terry
John Olsen04/07/2010 09:50:38
1078 forum posts
91 photos
1 articles
Well, here in NZ the authorities would not be very interested unless you were doing copies for hire or sale, or were doing it on such a scale as to impinge on someones business. But it would be a bit "in your face" to offer to make copies on the Model Engineers own web site wouldn't it.
 
One aspect of this in the past has also been that due to the various changes over the years, not to mention the bombing of the office during the Blitz, the Model Engineer itself has not always had a complete set of back issues available.
 
regards
John
 
 
Robert Hornby05/07/2010 01:45:56
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8 forum posts
13 photos

John,>>

Thank you very much for your reply to my query, I apologize for my galloping ineptitude in misreading the year date of the magazine and you obviously searched your stack of magazines for the article. I too am in the lace w:st="on">Antipodeslace>, although not NZ, I am in NSW Australia. If I may be so bold as to request that you email me carrob@westnet.com.au  maybe we can work something out. If so I promise to barrack for the All Blacks, but only for one game.>>

>  Also I thank Terry for your suggestions, I did try libraries etc. but with no luck.>

Robert>>

Ian S C27/11/2010 23:56:54
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7468 forum posts
230 photos
Hi Ray, wonder if you got your motor running. Was reading through the thread and thought no one asked what size flywheel you have, some motors need a reasonably large dia wheel. Ian S C
Mark Smith 328/11/2010 17:46:21
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166 forum posts
36 photos
Yes, like Ian I would be interested to know how you got on. If you have built it as the plans show you will have done a terrific amount of work for it all to come for nothing. Bye the bye, some engines will run at high speed with no flywheel at all, though they lack torque.
Mark
Raymond Griffin28/11/2010 21:08:00
53 forum posts
38 photos
Dear Ian and Mark,
Many thanks for your interest. A bit naughty of me to have left it in the air after all the responses on the site. Apologies all round.
I had the very good fortune to meet up with Roy Darlington at the Alexandra Palace show in January. He is a true gentleman and was happy to spend some of his time talking over my problem with Stirling Silver II.
He told me that many of these engines have been made, and that they normally run well. So well in fact, that if you try to stop it by holding the crankshaft you will end up with burnt fingers. His tips are as follows:-
Assuming that the engine is well made and that the piston is a good fit. Good fit means slides easily but gives good compression. 
There are generally two points to look for with Stirling engines, friction and leaks.
1. I was happy that my engine was as free running as possible without being sloppy. So did not feel that friction was a problem.
2. Check thoroughly for leaks. That includes the displacer. Put the displacer into hot water: bubbles will indicate leaks. No bubbles with my displacer, so onto turning the assembled engine over with the hot cap end held under water. Again no leaks. However, when I filled the back of the piston with light oil (I didn’t want to put water into the internals) and turned it over lots of bubbles came from the junction of the displacer rod and its bush. I had reamed the bush and must have used slightly undersized stainless steel for the rod. Have now replaced the rod with some slightly larger material. Shows that it pays to measure stock metal carefully before use. Also, to use the first part (taper section) of hand reamers and check for fit. It leaves scope to go further in with the reamer if necessary. That leak has now gone. 
I then decided to look at the timing of the displacer. The rocker arm that controls this is set at 83°. Roy said that it works well at this angle, but I wondered if tolerances etc could make my engine need a different angle. So I made a rocker arm that allows me to alter the angle. I found that when I adjusted to almost 90° the engine wanted to go. It was then that I saw 2 blue jets coming from the end of the hot cap when being heated with the burner. It looked as though high pressure gas was blowing the flame of the burner. I am fortunate in having a good stereo microscope in the workshop and examined the end of the hot cap closely. Several very small holes were apparent in the ring of brass braze. So I took it apart with the intention of re-brazing to fill the holes. I don’t want to make another hot cap
It was put on one side so that I could complete my Stockport vacuum engine in time for our local club show in February. Then I decided to build the Stuart Models Double Oscillator to go in a model tug. It is a great little engine and worth making. Then we were into summer. I live in the South of France where the temperature in the workshop can rise to 35° and I did nor relish the thought of adding heat with the blowlamp. I feel that the engine will go if I can seal these holes in the braze. I want to finish it for our club show in March, so there is some incentive, as well as the time already invested.
That is it up to date. I take the point about flywheels, but the plan calls for two flywheels in alloy. I have used a couple made of cast iron, giving plenty of weight.
Promise to let you know how it goes, over this winter. I will use a torch with a mixture of high temperature gas and oxygen to keep the heat in the region of the holes. My only fear is that I may burn a hole in the end of the hot cap. 
Best wishes, Ray.

Mark Smith 329/11/2010 04:12:46
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166 forum posts
36 photos
Thankyou Ray that was very informative, it just confirms the leak, friction and timing are the critical things. Interesting that stirling Silver II has that much potential power.
 
Good luck with the brazing, but also Ian's advice about running in is valuable. One of my engines refused to start and seemed to have too much compression, like yours; but after persisting it started and is one of the most reliable engines I have built
Mark

Edited By Mark Smith 3 on 29/11/2010 04:13:35

Edited By Mark Smith 3 on 29/11/2010 04:21:31

Richard Parsons29/11/2010 04:53:25
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645 forum posts
33 photos
Raymond  Know any one who does 'plating'  That might solve your dilemma.  Zinc however does not like brasss/silver and tends to strip away from the mother metal at about 200 C.
My Robinson has worse problems.  The alloy castings were all porous so i use it as a door stop.
Ian S C29/11/2010 12:29:27
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7468 forum posts
230 photos
I tend to favour stainless steel for the hot end, either tube with a cap TIG welded on, or carved from solid bar. I'v been trying to persuade some (that should know better),on another site that leaks in displacers do matter.
I'v only got one reamer, 1/4" adjustable, which is great for sizing holes. For steel shafts in brass etc I use a bit of the shaft and make a reamer out of that. I just cut a sloped bit at the end(about 15-20 deg), one or two holes no hardening needed.
Its quite interesting if you'r into experimenting, to make one of the cranks adjustable, you can then move it by fractions of degrees 'till you get best performance, then move 180deg and run the other way. But once you'r into that stuff, you want a way of finding rpm, and torque.
Mark, I had the Ross Yoke engine at the Kirwee A&P show last week, it ran all day in the rain making a good amount of power with the generator, the radio it was running stopped at one stage when it got full of water!

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