Are Stirling Engine Kits Hard To Build
Are they worth it?
I had to find out
To start off, I chose a small, inexpensive Build Your Own Stirling Engine Kit — advertised on Amazon.co.uk as the OEASY Stirling Engine Kit, being a DIY mostly Metal Stirling Engine with a small generator to provide electricity in a small way, not that I wanted flashing lights or anything like that, but that’s what was on offer.
I chose this one of the two cheaper options on Amazon.co.uk as I’m a bit of a scrooge, really, and as it was my first attempt at assembling these small engines I did not want to waste my money on something that was either delivered incomplete all the way from China, or not at all, and then have the rigmarole of waiting forever for non-delivered parts or needed lots of titivating to produce a working model.
On top of this, I was prepared to wait up to a month for delivery, but it took just ten days from ordering.
To be honest, for that price, I was half expecting a rough project that needed lots of trimming and filing so my hands would be shredded the moment it plopped out of the package, especially as I thought it would have been made in China, but to my surprise, it was machined very well and my skin remains its usual roughness.
The other one I saw with exactly the same arrangement as the one above offered by a different seller with a higher price but with immediate delivery if I used Amazon Prime, goes by the title of the Fydun Stirling Engine Model, External Combustion Stirling Engine Motor.
There could well be more variations of this model on offer worldwide going by different names and possibly made a little differently, as I believe many Amazon advertisers simply re-list Banggood products on Amazon using their drop-shipping arrangement, as I feel mine was. However, I am more than happy with my engine and the delivery time, but there were a few hiccups along the way when testing time came, but more on that later.
Over in the States, this same engine is advertised as the FenglinTech Stirling Engine Kit, DIY Assembly Stirling Engine Generator Model Toy, just to confuse us all the more.
On the other hand, if you want a cheaper version of a similar self-build Stirling Engine, I’ve found one with a much simpler layout.
In fact, I reckon a five-year-old child could complete this working engine without too much difficulty – with adult supervision, of course, owing to the naked flame and possible mix-ups owing to communication problems.
This one comes directly from Banggood in China (the equivalent of Amazon in the Australasian parts of the world) so no middlemen making a profit from your purchase before adding extra to the price (unless you click my link below where you’ll get the model for Banggood’s price, and it includes free delivery – makes you wonder how they can produce such finely worked models at that price, doesn’t it), but the delivery time is estimated to be two to three weeks, like mine was.
It is called the STEM Stainless Mini Hot Air Stirling Engine Motor with lots of happy customers recommending this simple model and the layout of the port between the cylinders is already done for you, so no perishable transfer tube on top.
It stands on a single column on a base plate attached by three screws, basically a single mounting point doing away with a lot of the fiddling, so being made and assembled in one unit, the engine should not shake itself to bits too easily, plus this makes it a dead-simple project.
But back to my more fiddly Amazon purchase
The ad says it is suitable for adults and kids, so maybe I’ll stand a good chance of completing this model without any issues, but I intend to give you the full details of the construction as we go along as the instructions supplied were a bit like gibberish, even to my educated head — not that I’m bragging, or anything like that.
It comes in kit form as shown below and as you can see, both a screwdriver and Allen key are included for the construction, but I had my doubts whether they were good tools or not before construction began, which proved to be wrong.
Delivery Of My Stirling Engine Kit
This engine was ordered on the 31st of January and the delivery estimate was for around the 20th of February, so we can all guess where it originated at such a low price of around 30 quid. ——- For a wild guess, I’d say it was from Banggood in China since finding that site in my searches, although they do have outlets around the western hemisphere so it could have come from anywhere.
It arrived on the 9th of February and I have to admit I was eager to get on with the construction of this kit, although the instructions were extremely vague with the different language translation problems we face regarding Chinese produced products.
I must have spent over half an hour trying to understand what was written, despite the fact a lot of it was shown as pictures and captions on a single sheet of polished paper.
In the end, I looked at the picture of the finished product and started from there – a bit like self-assembly furniture?
The base plate is steel and there is a single flat magnet attached to it which I failed to understand why it was there until later as it is part of the kit.
This magnet is simply to keep the steel alcohol reservoir in place, making it easy to slide it to a better position under the end of the displacer cylinder to achieve better control of the heat source as can be seen in the top image.
My first thoughts after opening the fully intact package and laying all the parts out in front of me, were, why is there an odd bit of blue, threaded, plastic bottle cap in there?
Seems there is no wick, but the alcohol burner is 2/3 filled with alcohol (preferably de-natured so it provides no soot), but no other suggestions regarding what to use as some sort of wick, so I added cotton wool pushed down to the bottom with just a little poking up through the top so it stayed above the top of the container.
This worked well once I got it going, but the only control is to move the container around under the hot end to get some sort of speed control.
The plastic part (blue bottle top), I can only surmise, is to place on top of the alcohol canister (once it is cool) to stop the fuel from evaporating when not in use, but I doubt that would work anyway as it is not an air-tight fit on the metal canister. I suppose it could also be used to douse the flame by popping it on top of the flame, limiting the oxygen supply, but that seems daft to me, considering it is plastic and a light blow across the flame puts it out.
How to Build Your Own Stirling Engine Kit
The kit comes with a pad (not shown on the parts list) of self-adhesive black foam with 4 pre-cut circles that need pushing through with your thumb, each one attached to the corner underside of the steel plate to act as a stabilizer and to raise the plate up to allow for the screw heads. Maybe, also, to stop it from traveling or vibrating along your desktop when running.
So here you’ll need to see which is the better-finished side of the 8 x 16cm plate (that’s 3 and a bit x 6 and a bit inches, now we are out of the EU. Thankfully, I can go back to the measurements I grew up with and still use regularly) to use as the upper side and add the foam pads to the underside, one in each corner.
You will see the well machined and finished plate has seven pre-drilled holes and these are to allow the seven screws to attach the three main parts on the upper side of the plate.
These three parts are:
- The crank/flywheel/generator pulley
- The displacer piston/cylinder
- The power piston/cylinder
There are two piston/cylinder stands with two pre-screwed holes in the feet, while the crank/flywheel/generator pulley stand has three pre-screwed holes in the base so it is pretty obvious where this last one goes on top of the plate.
The “parts” image above shows an exploded view of each cylinder with lots of fiddly parts to be put together, but fear not, the engine comes basically as three main sections with both those cylinders ready completed, just to make your life easier, but you need to check them out (see below in red).
The crank/flywheel/generator pulley
Taking the crank/flywheel/generator pulley section first, you’ll need to set the two steel crankpins sticking out of the brass flywheel and brass generator pulley on the other side of the bearing at 180 degrees to each other, not like it says at 90 degrees on the drawing.
This confused me a lot when trying to understand it all from the drawings and the written wording.
The flywheel and pulley are locked to the crankshaft using grub screws and these are tightened or released by turning them with the Allen key.
With the flywheel side closest to you, the flywheel needs the entry for the Allen key to be at the top (twelve-o’clock) while the entry on the generator pully needs to be at 1/2 past the hour. That way they become 180 degrees apart and the generator pulley follows the flywheel pully by 180 degrees, as do the steel pins for the piston rods
What the plan says, to give you an idea of what you will be dealing with, word for word in boxes is “The big wheel pin vertically to the down and then tighten to the.”
The plans are very much like this all the way through with sentences not complete with each picture well away from what the wording refers to.
Please ignore the black screw-driver handle in the pic. sloppiness on my part for not clearing things away.
Just to give you an understanding of how these engines work –
The steel tube sticking out the front of the flywheel-side cylinder (displacer cylinder) is attached to the main body of the displacer stand by a screwed fitting – can’t call it a nut as there are no flat sides to it, but it works as a compression fitting.
The big problem here is to make sure this tube is aligned with the internal glass displacer tube which reciprocates inside the displacer stand and this reciprocating displacer tube is supported only in one place by a synthetic sealing ring at the crankshaft end of the displacer tube.
This means the displacer tube may be sitting slightly off from the straight it is supposed to be in. Also, the open end of the displacer tube is held in place by compressing this sealing synthetic ring up to the main body.
This means the hot end of your displacer tube (away from the flywheel, could well be sitting offset inside of the steel heating tube, which can make odd sounds which means unnecessary friction and this is something you do not want in such an underpowered engine.
Upon further inspection, I found a hole in this piston allowing any supposedly compressed air, because of the heat, to pass through this piston, so I checked the other piston to find it was sealed properly.
Seems the sealed one needs to be for the power piston and the holey one goes on the displacer side of the engine, but the drawing doesn’t show it this way. Obviously, these pistons had not been assembled correctly at the place of manufacture – such an insignificant mistake caused me a few days of frustration, but now she works fine.
Before I stripped it down, I found the engine would turn over readily when heated, but not run. After a short time, there appeared to be a grinding sound before the crankshaft locked up towards the front end of the stroke.
What was happening was that as the sealed piston was in the glass displacer tube (piston) the air inside was heating up considerably and this forced the tube to travel away from the piston sitting inside the tube.
This meant the glass tube was moving forward into the steel heating tube and pushing it away from the flywheel end.
As the steel tube got further away from the main body, it went cock-eyed, twisting offline, meaning the glass tube was firstly rubbing the side of the steel heating tube, before it pushed it far enough for the piston on top of the conrod to pop out of the glass displacer tube.
A bit difficult to visualize, this process, but I was very lucky I questioned why the steel tube seemed to be sticking out further each time after it cooled down and it freed off. At least the glass displacement tube (cylinder) didn’t get shattered.
So back to the build we go…
Next, you need to slip the elastic band, the “drive belt” over the back of both pulleys, one on the crankshaft and one on the generator before slipping the ends of the diode into the fine holes on the generator poles.
This is a very fiddly process, especially if you are like me who needs a magnifying glass to find my glasses.
One in each hole is required as can be seen in this image.
Once in place, bend the diode wires over to provide contact, slip the drive belt onto the pulleys and spin the flywheel. This turns the generator and should cause the diode to light up, red first then going onto white, according to the speed of rotation.
Looking at this image the rotation is clockwise.
If it fails to light up, try turning the flywheel in the opposite direction.
If there is light produced, then remove the diode and replace the wires the opposite way round and try again.
You will find the flywheel needs some force to get it to spin fast enough to light up the diode, but if that fails try the other diode as a replacement. After all, they do supply you with two.
So we now have the timing set and we know the generator and diode function correctly, so we now need to install the crank/flywheel/generator pulley in position on the base plate.
This is simply achieved by screwing the foot of the crank/flywheel/generator pulley to the base plate, but this proved a heck of a problem for me with non-nimble hands.
As I am a fully paid-up member of the shaking hand society, something to do with age, I believe, I had to use a vice to grip loosely between paper-covered jaws, the base plate sideways on, acting as a third hand so I could hold a screw on one side of the base plate while my other hand held the crank/flywheel/generator pulley to the upper face of the base plate.
Not only that, but I am also a fully paid-up member of the fumbling hand society where there’s not too much feeling, so the size of the screwdriver provided makes it awkward to hold and turn at the same time.
One tip here is to magnetize your screwdriver by stroking the steel end along the magnet a few times, that way the short screws are readily held by your screwdriver, even when held horizontally and being shaken a little when trying to poke the screw into the hole in the base plate was no problem.
I got around this by firstly using the now magnetized screwdriver to push the screw into the hole and offered the crank/flywheel/generator pulley to it while rotating the part against the screw.
Once I had a small section of thread engaged, I used a very small flat ended screwdriver, barely engaged in the Philips slot and managed to rotate that to pull the two parts relatively close together, just enough to allow the other two screws to be engaged and tightened up, before using the small Philips screwdriver supplied to pinch up the base of the crank/flywheel/generator pulley.
Should have mentioned – the flywheel sits on the left-hand side of the three screw holes as you look along the plate with the three screw holes nearest you.
Installing The Stirling Engine Displacer Cylinder Assembly
Here we see the displacer cylinder with its appropriate displacer piston and conrod directly above it.
The cylinder itself comes as is, ready assembled, so no worries there – unless, like me, you assumed they are already set up right – do check out those pistons. This one needs to be vented (not hold air)
The piston sits inside the displacer tube which, like a test tube, is sealed at one end and has to be pushed into the end of the tube.
Sounds confusing, but the piston has the equivalent of two piston rings which need to grip the inside of the displacer tube and push and pull the tube along the glass cylinder bore.
I initially set the piston into the tube with the bottom end of the piston level with the bottom end of the displacer tube, but once assembled like that, the crank was stopped as the glass tube was hitting the other end of the grey tube.
Because of this, as the full rotation of the crank is needed, the piston needs to be inserted further into the piston tube for at least 1/4 inch for now.
The true size is a little more, but this can be sorted once the cylinder is installed on your base plate.
You will notice the conrod has 4 holes at its bottom end and the hole we will be using is the furthest one from the piston head.
So let’s install this displacer tube…
You need to insert a screw through the plate at the left/top hole as you look from the back of the plate. This means the furthest hole of the paired holes on the left-hand side as you look beyond the flywheel.
The darker glass end of the displacer cylinder sits forward and the screwed hole at that end of the foot is the one we shall be screwing into first.
You need to not overtighten this screw and keep it to a loose fit so that the piston can be attached easily, but do not insert the displacer tube into the displacer cylinder yet.
Next, we need to install the power cylinder before adding the power piston.
Again, the set-up is the same using the front hole in the plate on the right-hand side, with the fancy front end of the cylinder at the front and the glass tube at the rear.
Do not overtighten the screw as we need the cylinder to rotate slightly to install the piston and con-rod.
Now we come to another fiddly bit (on my part)
You will have, as you look from the front end with the flywheel furthest away from you, both cylinders standing upright, the power cylinder on the left and the larger displacer cylinder on the right.
So what’s needed now is to attach the con-rods to those steel pins sticking out of the brasswork of the flywheel and pulley on the crank/flywheel/generator pulley assembly.
Here, I suggest you insert the power piston con rod first. By turning the power cylinder body sideways to the left, you can insert your piston into the glass tube of the power cylinder body and then turn the power cylinder body back to engage the steel pin on the pulley through the last hole in the con-rod away from the piston.
Now here comes the fiddly part.
You have been supplied with small sleeves to slide over the end of the steel pin, a bit like a biro tube that carries the ink, but much smaller in diameter, and one of these need slipping over the end of the steel rod.
Its purpose is to hold the con-rod in place, to stop it from coming off the pin.
I’d suggest pushing this sleeve on to allow just a fraction of space before it rubs against the con-tod.
One tip here is to sit a sleeve on end on a flat surface and wet the end of your finger, dab your finger onto it and it will stick to your finger to make it easier to install it on the steel pin.
But don’t drop it as it will bounce anywhere and as they are so small, you’ll maybe lose the odd one – and was I grateful three were supplied in my kit of parts.
Once the con-rod is attached, the second screw can be added to the foot of the power cylinder and both screws can be screwed in tightly to align the cylinder properly.
The displacer cylinder can be attached in the same way, but here you need to be aware you may need to slide the steel piston along the glass displacer tube (piston) a little further to slide the crank pin into the last hole on the con-rod.
If you couple up the con-rod and cannot get the flywheel to do a full rotation without the tip of the displacer tube hitting the end of the grey tube, then you need to move the piston along a little.
When no sound is heard with the crankshaft being rotated by hand, then you have the right position for the steel piston.
Another point is, as these tubes are glass, they can break easily, especially this one as it reciprocates inside an iron or steel tube and is heated considerably, so you need to make sure you have the necessary clearance between the end of the displacer piston tube and the grey one.
When the engine is running, heat expands the displacer piston tube more than the grey tube, so it will be safe to run this engine, but when assembling, make sure you don’t drop these glass parts or they will shatter.
Now you have her assembled, to check everything is fine, hold a finger over the small tube sticking up from the power cylinder.
This should have an effect on the flywheel being rotated where it limits the movement of the piston within the power cylinder.
Now try it with your finger over the one on the displacer cylinder.
You’ll find this one turns ok as you have more air inside so it means compressing the air is easier.
That shows everything is OK.
Here’s where you need to link both cylinders together with that small pale tube. Just push it on at both ends and you are ready to fire up your home assembled Stirling Engine Kit
Lubing it up
I’d suggest once you’ve run your Stirling Engine Kit for more than ten minutes, the fuel will be near enough gone, so let it cool down naturally for half an hour before dabbing a touch of lube on all moving joints.
Keeping away from the pistons is a must as there’s not much clearance for a purpose on an engine like this, so adding friction by gathering dust on the sides of the pistons is not wanted.
Sewing machine oil or something very light like 3 in 1 oil does the trick, and it needs a pin dipping in the oil and just touching the joints – any more and you’ll be adding to the unwanted friction.
My thoughts on this engine…
All-in-all, it is very well made with all surfaces and edges trimmed correctly so no sharp edges can do any damage to the builder.
It is very inexpensive and produces a great working model.
My first problem was understanding the build instructions – that’s why this every-day English build guide has been produced.
Because of the size of this engine, you need to be dextrous to complete this easily.
My first build time, with all the non-understood instructions, was around 2 hours, but now I know the layout it can be done from scratch in around 12 minutes and running in 15.
Here are the links again should you want to jump in and build your own Stirling Engine from a Kit
Or perhaps you want a Ready Built Stirling Engine similar to the above, then how about this one?
Comes with free delivery, ready-made, and around the same price as the kits, and best of all, no fiddling – and you’ll notice there are a proper wick and fuel pot included…
If, on the other hand, you feel more inclined to completely build your own sterling engine from scratch, take a look at the great variety of plans, including Stirling Engines, all available on our free download page, just by clicking this green tab.