Sterlin Engine not working

[Kayjas]

I have inherited my father's machine made Sterlin motor. Many years ago he got it working but was a real struggle to get it to start.
Now it won't start at all. I have cleaned all the parts and reassembled and it made no difference.
I made a new piston and changed the length of the displacer shaft so the displacer goes to the end of the tube as it wasn't going all the way.
I have also eliminated most of the friction and it turns freely.
I'm heating the end with a mini cooking blow torch.
So what am I doing wrong I would dearly love to see it working again.
I have the capability of making new parts.
Thanks in advance

[Kayjas]

I have inherited my father's machine made Sterlin motor. Many years ago he got it working but was a real struggle to get it to start.
Now it won't start at all. I have cleaned all the parts and reassembled and it made no difference.
I made a new piston and changed the length of the displacer shaft so the displacer goes to the end of the tube as it wasn't going all the way.
I have also eliminated most of the friction and it turns freely.
I'm heating the end with a mini cooking blow torch.
So what am I doing wrong I would dearly love to see it working again.
I have the capability of making new parts.
Thanks in advance

[Tom Booth]

What is inside the transfer port? The big aluminium block between the displacer and power cylinders?

chamber2.jpg (336.55 KiB) Viewed 2348 times

The space, or at least what can be seen of the opening, looks unusually large. If so it looks like that area could represent a lot of "dead air space". That is, a volume of air inside the engine that is not heated when the displacer moves.

Just guessing, as I can't see inside there but looking at the opening it looks like it could be a large open space inside that big square block.

If so, that much dead (cold) air, relative to the air moved by, what looks like a possibly too small displacer could have the effect of diluting the hot air produced when it passes through from the displacer chamber.

[Kayjas]

Hi. Thanks for reply. I have added some more photos for you to look at. Thanks again

[Kayjas]

I've also tried different lengths of displacers. No difference at all,

[VincentG]

I can't tell from the pictures if the hot cap has a seal on it. If not, work on getting that to seal 100% to the engine block. There must be no air leaks here, as there are likely air leaks from the displacer guide rod and power piston already.

Adjust the displacer so that it comes as close to the engine block as possible when traveling in that direction.

Use thermal paste where the heat sinks touch the hot cap.

Put some light machine oil on the displacer guide rod and power piston to help them seal.

Make sure the assembled engine spins very easily with no binding.

Finally, disconnect the power piston from the beam and rotate the crankshaft by hand with heat applied. If the power piston does not freely move at least 25-50% of it's total stroke, it might not run at all.

[Tom Booth]

Doesn't look like "dead air space".

What do you use for gaskets or sealant.

The parts look clean. No gasket residue or silicone or anything.

The connecting rod looks like it has a rather rough surface and the gap between that and the bushing looks like ants could crawl through there

Compress_20240825_094724_4112.jpg (26.8 KiB) Viewed 2306 times

I assume you've checked for air leaks.

Maybe the fit is tighter on the other side.

Anyway, you probably already know ways of finding leaks but spraying some soapy water on all the seams and potential gaps and gaskets while turning the engine over.. look for bubbles.

Have you tried a little oil?

If it was hard to start to begin with, and then ran for some time, a little wear could make it harder.

Some engines are rather loose and don't seal well until good and hot which tends to close up the gaps. A bit of oil can seal up the gaps to help get it going.

[Kayjas]

Hi all
Thanks for the advice. I've adjusted the displacer as recommended and used some sealer. I've eliminated as much friction and any snags and I can spin the flywheel and get a few revolutions freely. Still can not get it started.
Is it possible the cranking is wrong? I've tried many possibilities but feel limited with the crank shaft.
There is small leakage where the pull rods go through the block but have changed and polished the rods. Any tighter and they would bind.
I feel I'm missing something really fundamental with the geometry and sizes of piston length and fine tuning.
Cheers
Alan

[Tom Booth]

Usually with a walking beam type engine the pp is on the side and displacer vertical.

The displacer rod passing through might present some timing issue. That can be difficult to diagnose without hands on access to the engine, especially being uncertain about the intended direction of rotation.

I'm not familiar with timing that particular style engines but if you could take a video showing the engine rotation it should be possible to figure out.

As far as I can figure, from this image:

IMG_20240825_074203.jpg (116.21 KiB) Viewed 2250 times

I believe the flywheel should rotate counterclockwise. That is, the top of the flywheel should move away from the engine.

[Tom Booth]

Where do you apply heat?

Also, what material is your displacer made of?

There is some controversy on the subject and different opinions, but in my experiments I found a metal displacer, especially aluminium can conduct too much heat too quickly, basically acting as a heat pipe transferring heat to the cold end making the engine difficult to start as there is less temperature difference.

You might try replacing the metal displacer with a wooden dowel of the same diameter and about 1/2 the length of the displacer chamber, then only heat the tip end of the displacer chamber.

The wood may char a bit on the end if you get the chamber red hot but it would just be a quick test to see if that makes any difference.

I found it made a tremendous difference on some of my own engines, starting up much easier and requiring much less heat to keep running.

[Kayjas]

Hi
I've used both brass and aluminium for the displacer but will give wood a go.
I apply heat towards the end of the tube.

Is there sine guides on setting the timing of the piston and displacer?

[Tom Booth]

"sine guides"?

Generally, with the piston and displacer at a 90° offset as in that engine you can't really go wrong, as long as the rotation is in the right direction.

[Kayjas]

On further strip down I found some swarf in the air exchange hole and grease. I will carefully clean and reassemble with fingers crossed.

[Kayjas]

Nope... The clean up didn't work. However when it all gets hot I get smoke coming out from the sides of the piston. Is this telling me the piston is too loose. It's made from aluminium and does pop a very small amount when you pull it out. Thanks

[Tom Booth]

Nope... The clean up didn't work. However when it all gets hot I get smoke coming out from the sides of the piston. Is this telling me the piston is too loose. It's made from aluminium and does pop a very small amount when you pull it out. Thanks

I'd clean the displacer and displacer cylinder very well also. If you haven't already. I assume the smoke would be from there where it's heated.

I found that smoke from burning grease or anything can very quickly gum up the power piston causing drag like glue.