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myfordboy's E Z STIRLING ENGINE



I have simplified the original Tin Can Engine  to make it easier to build and to use materials that are easily available. No soldering is required and it can be made using only hand tools.
The engine would make a good Science Fair project and demonstrates the principle of the Stirling Cycle or Hot Air engine. Many engines have now been built and feedback has been received from students who have submitted engines as collage projects and it has help them achieve high grades.




Here's what you need:
Your FREE  plans sheets. Send an email to ( myfordboy[at]yahoo.co.uk ) and I'll send you a PDF copy you can print out yourself ( replace the [at] with @ in the email address, this is to stop spammers finding my email ). The address is also given again as an image after  "How it Works"  lower down the page.
I will send the file to you as soon as I see your request  but don't forget I may be out when it arrives. Also remember I am in the UK so I could be in a different time zone than you.
The engine has been very popular and I am sending out about 90 plans a week at the moment so If you do not get your copy within 24hrs please ask again in case your email got missed.
If you put "E Z Stirling" as the subject in your email this will ensure it does not go to my spam folder.
 
200g Travel sweet tin, eat the sweets! The tin is 97mm diameter and 40mm high.
 If you cannot get a sweet tin click here.
150mm x 150mm of 3mm MDF or good quality plywood.
3  3.2mm x 6mm long stainless steel Pop rivets. The aluminium ones aren't really suitable. I bought a packet of 10 from an Ebay shop for £1.30 including postage.
Thin steel wire, about 1 mm diameter.
1 Latex  glove.
1 compact disc. A colourful one looks best.
100x 200mm of 9 mm Balsa wood.
4 small screws , these can be obtained from broken toys or calculators.
2 small screws and nuts. (8BA or 2-56 or M2, depends where you live!).
Cyanoacrylate glue. (super glue).
Silicone sealer.
PVA adhesive.
Cotton thread.
Short piece of electrical cable.
Adhesive tape.
Thin steel wire, e.g florists wire.

For the burner you will need:
Small glass bottle with metal cap. Look in the pharmacy. Mine had essential oil in it.
Cotton String.
Baked bean can.
Copper wire.
Plastic bottle top.
3 woodscrews.
3 screws and nuts.

Alternative Materials
Some builders have mentioned that they cannot get balsa wood or the specified sweet tin.
Using a much larger tin will alter the design and it may not work.
Click here to see suggested alternative materials for the tin and displacer. 
There is a link to a further video showing the methods of construction.
Building Tips
Print out you template sheet. It's drawn A4 size. You can check if your printer setting are giving the correct size by checking the length of the horizontal and vertical scale on the sheet. Its not that critical a 1mm error is fine. You may have to adust your printer settings to get it the correct size. On my HP printer I select "Print Actual size" and check the "Choose paper source by PDF page size" box.

MDF can tear when holes are drilled in it, depending on the quality of the product.
On parts like the flywheel hub where accuracy is needed to locate the hub, superglue can be applied to the part before it is drilled and this will make the MDF much harder. I also apply a coat of superglue to the base parts and let it dry . This stops the glue soaking into the MDF when the rubber glove diaphragm is fixed.

The following tips corresponds to the Youtube video timeline.

Time
01:48  The parts are drawn actual size but I suggest the strips at the top right are left a little overlength and sanded back to size after they have been assembled.

04:50  Position the vertical part to the just meet the large hole in the base.

05:28  If you don't have a pillar drill, I suggest carefully marking and drilling the holes
from both sides. Drill the hole 3.2mm dia and 7.0mm down from the top.

06:40  Disposable latex glove is used.

07:00  Before fixing the diaphragm, the base has been primed with a coat of superglue and left   to dry.
 
07:46  Do not stretch the glove too tightly but ensure there are no wrinkles.

09:20  This template has a circle drawn in the centre as an alignment aid for the small MDF disc.

09:43  The small MDF disc that was cut from the plans is used to attach the displacer rod to the diaphragm. Drill a small hole in the centre and the rod is a push fit. A small drill could be made by using a bit of the same wire used for the rod and shaping the end like described below (11:43).  If the fit is a little loose a spot of glue can be used.

11:00  This joint must be completely airtight. If not the engine will not run. The biggest cause of a non running engine is an air leak,

11:30  Removing the "nail" from the Pop rivet.

11:43  These parts are used for the crankshaft bearings and the displacer gland. It is most important that the fit is very free with little friction. I found the nails that came with the stainless Pop rivets had a slight bend in them which made them unsuitable. I substituted a steel nail from a similar size of aluminium rivet. If you can feel any rough areas on the nail then carefully smooth with a fine file. Metal polish can be used to get a free running bearing and if all this fails, make up a simple reamer like shown below by filing a flat at an angle on a pop rivet nail.  Hold the rivet head and work the reamer up and down whilst applying a twisting motion.




11:46  A blob of silicone sealer to ensure the gland is airtight.

13:36  This template has a point marked in the centre to mark the lid centre.

16:10  This hole does not need to be neat. It only provides clearance for the power piston and won't be seen when the engine is finished. Use a fine file is you don't have a Dremel
or similar tool.

16:50  This hole is 18mm diameter. Its size is not too critical. It has to give clearance for the small disc on the end of the crankrod.

17:35  Pilot holes are drilled for the small screws.

18:20  This is bathtub sealer.

20:00  It is important this joint is airtight. If not the engine will not run. The biggest cause of a non running engine is an air leak. Clamp and leave to cure overnight.

20:19  Roughen the CD with sandpaper to give a key for the superglue.

20:30  Use the template to centre the hub.

21:00  The crankshaft is 20mm long.

21:12  Try to get the disc to run true before the adhesive sets.

21:17  The crankpin is 11mm long.

21:50  Position the wood grain at 90 deg .

22:30  The diameter of the displacer is 9mm less than the outside diameter of the tin. This gives a gap of 4.5mm between displacer and tin.
Mine came out at 88mm.

22:40  Use the full length of the Pop rivet nail for the displacer rod.

24:38  Make the bend 6mm from the centre of the loop.

                                                                Displacer  crank

24:52  The connecting rod is made in a similar way to the crank. Its length can be adjusted later.

With the crankpin in the horizontal position make sure the diaphragm is not pushed up or down. Rotating the flywheel should give the diaphragm an equal up and down movement.

25:35  The flywheel must rotate very freely.

26:38  The crankpins should be positioned 90 degrees apart, i.e. when the displacer rod is at the bottom of it's stroke, the diaphragm rod should be horizontal (left or right determines the direction of engine rotation).

28:35  Cable insulation holds the thread to the the displacer rod.

29:16  Adjust the length of the thread so that the displacer nearly touches the tin lid. When assembled with the tin bottom the displacer should move up and down without touching the top or bottom. If this cannot be achieved then a shorter crank should be made.

29:28  Tape is used as a temporary seal to test the engine. Later silicone sealer can be used in it's place.

32:20  Lamp oil is used in the burner. Only a very small flame is needed. The larger the flame the faster the engine runs, this is not meant to be a high speed engine though considering the materials it is made from.
A larger glass bottle is better for the burner than the one in the video. As the small one heats up  the fuel vaporises and causes the flame to get larger. This overheating could result in damage to the engine.
An improved design is shown below. This a vinegar bottle with a brass plumbing end cap and small copper tube fitted. A taller can is needed with this burner but it will burn all day without flaring up.



Apply a drop of oil to the crankshaft and on the crankpin. Also put a drop on the displacer rod where it enters the top of the tin. This will lubricate the rod and help make an airtight seal.

Fault Finding

What if it doesn't work?
Firstly check the parts run very freely like mine in the videos. There is little power in this engine so it needs to be a free as possible. Make sure the connecting rod eye is square to the flywheel and not binding.
Make sure the displacer crank and flywheel crank are positioned 90 degrees apart.
Check for air leaks.
Disconnect the connecting rod from the flywheel. Place the engine on the burner and move the  displacer up and down by pulling on the thread. If there is little or no movement of the diaphragm, you have a leak somewhere. Check the displacer gland and the seal where the base is attached to the can lid.  Maybe your engine runs but only for a short time, squirt some WD 40 oil around the outside of the MDF base whilst turning the engine over. Any leak will show as air bubbles. Don't do this if your MDF is not painted as it will soak into the MDF and swell it up.
Your diaphragm may be too stiff. On the gloves I have used a squirt of WD40 softens up the diaphragm. With the flywheel disconnected and the displacer operated by hand the connecting rod needs to be able to move slightly more than the crankshaft throw.

I have just replaced the diaphragm on one of my engines after many hour of running. When I tried it again it would only run for about 6 revolutions and then stop. Using the method above, a leak was detected at the front where the base meets the tin. A fillet of silicone was applied in this area and the engine is a runner again.



If you cannot get you engine running and you are sure it  turns freely with no tight spots then it must be an air leak preventing it from running.

Make a pressure tester
 As mentioned above the most likely cause of a non runner is an air leak. Pay particular attention to where the base meets the tin top and where the two wooden parts sandwich the diaphragm.
Get hold of another sweet tin and poke a small hole in the side near the base using a nail. Attach a short length of small tube using epoxy or car body filler. Mine was copper but could be any material, plastic is OK perhaps from a ballpoint pen. Be sure to seal where the tube enters to make it airtight. 
                                                              Pressure Tester 

Now fit a short length of flexible tube as shown above. Fit the engine top to this temporary bottom and seal with tape as before. Gently blow into the tube. The diaphragm will be pushed up and if there are any air leaks you will be able to hear a hiss as the air escapes. Apply a fillet of silicone if it is around the base.

An air leak is the most likley reason an engine will not run.
Constructor Mathieu recently wrote after his engine would not run,
" It works! After spending like an hour on it, I finally found out what was my problem. I did what you are suggesting and I used another tin to make a pressure tester. I simply used a straw with some epoxy and when I blew in the straw, I immediately knew what was wrong, it was the only thing I wasn't suspecting, my temporary tape seal!
I didn't take extra care when I put the tape and it was indeed leaking with my pressure test tin, so I figured it was probably the same with the other one.
I used another type of tape and resealed everything cautiously and voilà! "


Here is a short video of things to try if you cannot get your engine to run. 




How it Works

The principle of the Hot Air or Stirling Cycle engine is not well known. It is difficult to see how it can work just by applying heat.
If we take an empty can and stretch a piece of balloon over the top, like the diaphragm on our engine, the air is sealed inside.
Apply heat to the bottom of the can and the pressure inside the can will rise and cause the balloon to rise a little.
Now if the bottom of the can is cooled by placing it in a dish of water, the air inside will cool and the pressure will fall. The balloon will be sucked inwards.
So to get our diaphragm, which is a simple form of piston, to drive our engine all we have to do is alternately heat and cool the can.
This is not very practical but the same effect can be achieved by heating one end of the cylinder, the bottom, and the moving the air inside alternately from top to bottom. This is the function of the displacer.
The displacer takes up space inside the cylinder, when it’s at the top, all the air inside is displaced to the bottom where it is heated and expands.
When the displacer is at the bottom of its stroke, the air is moved to the top, which has a cooler surface, and it contracts.
Remember, the displacer does not touch the sides of the cylinder. It is not a piston. As it rises and falls air passes around it as it is transferred from top to bottom. It’s the same air that is continually heated and cooled.
For the engine to work the top has to be cooler than the bottom.
The larger the temperature difference we can get, the more powerful the engine will be.
The configuration of the cranks and connecting rods allow the displacer to move in the correct relationship to the diaphragm and flywheel.
When you have your finished engine in front of you, it will be easier to understand the principle.



Animation supplied by Draco.



 If you do build one of these send me a photo I can add it to the gallery  for others to see.

GALLERY of  E Z STIRLING ENGINES by other builders

 More Stirling Cycle Engines

The engine described has little power and serves to demonstrate the Stirling cycle principle.
The Stirling cycle can been used for developing real real power though, some examples are shown below.





The Essex Hot Air Engine




The Essex Hot Air Fan




The Sugg Engine