stirling 60 build

[anday1]

hi
i have just completed the Stirling 60 engine looks great but has problems getting going...used a cast iron bearing in the cylinder and i have turned a graphite piston for the power cylinder ..but with no groves. it spins freely but I,m still wondering where I've gone wrong.

any help would be gratefully received

regards
andrew

 

[minh-thanh]

Welcome !

 

[Technical Ted]

I've built 3 of these and also have helped others with similar problems... they seem smooth, but just don't want to run. Do some searching in this group (and others) and you'll see some posts including this one:

https://www.homemodelenginemachinist.com/threads/stirling-60.30328/
In my experience with this particular model, it's always been the horizontal CI bushing for the displacer rod. The weight of the linkages and displacer can cantilever and bind up very easily. Trust me, it doesn't take much bind for these not to run. IT's hard to feel this by turning the flywheel by hand. The hole in the CI bushing MUST be perfectly straight and concentric. Any misalignment will cause binding. If I were to build another one of these, I would modify the design a little making this CI bearing as long as possible to better support the displacer/linkages to keep it from cocking off. Being so short (per design) acts as a pivot point for the displacer rod to titter and bind.

These models are beautiful and I love them, but they can be difficult to get running properly with just the tea candle. Some have given up and used a higher heat source which has worked, but I want mine to run off the tea candle because that's one of the things that makes this model so special!

Good luck,
Ted

 

[anday1]

thanks, Ted
I made the CI on the lathe then drilled 1.9 mm and then reamed it with a 2mm reamer then used a scrap bit of the rod steel with fine cutting paste and spun it to get it really smooth....then and this is where the error might have come, I inserted it and locked it in the cylinder with lock tight. what I might try is all the above but put it into the cylinder first then do all the drilling etc. the power piston I made from graphite. I'm not sure if going into brass as opposed to glass or perspex which I've seen before is as good. would you recommend making it out of CI or brass?

all the best

andrew

 

[Technical Ted]

Drilling/reaming the hole in the horizontal CI bearing is where the trouble is.... most likely the hole did not drill perfectly straight. Small drills will walk off center very easily. Just drilling/reaming typically won't cut it. Measure the wall thickness all the way around the bearing on the far side where the drill exists and I'm betting you'll find it's off center from the small drill wandering. I played with ways of getting this hole concentric by using a drill chuck in my compound tool holder vs my tail stock and had some success, but the easiest/best way I found was to turn the OD oversize and drill the hole. Mount the bearing on a piece of whatever you are using for the rod and super glue it so it's secure. Mount it up in a collet and then turn the OD to final size. There's more than one way to skin a cat! But trust me this hole must be perfectly concentric.

I followed the design materials to the letter. Brass cylinder and piston, brass displacer, CI bearing for displacer rod, etc.. All that is good. One possibility with your model is the weight of the displacer... I made mine very thin with ~0.015" walls from a solid piece of 360 brass. You need to keep the weight as minimal as possible to help with the cantilever binding in this design. If your glass displacer is heavier this will cause additional issues. I know of one guy who ended up making his out of aluminum to minimize weight and it seemed to help. You can make them out of free machining brass very thin, but you need to sneak up on things very carefully. I've posted how I did mine so maybe if you do some searching on this group and HM site you'll find my multiple posts on this subject where I made mine and helped others.

Not sure why you have the screw adjustment on one of your linkages.... All my parts were made to spec so you might want to check that your linkage is set at the proper length for the proper stroke...

Also, don't be afraid of putting a drop of oil in the horizontal CI bearing, especially when first trying to get it running. I would NOT oil the power cylinder as burnt oil soot will build up and then the engine will stop running until cleaned. Keep the oil out of the hot running components.

Ted

 

[Technical Ted]

Here are videos of mine running. In the video with all three you'll notice the one engine in the middle up high is running slower than the other two. This was the first one I made (one for my wife) and I learned from making that one the importance of this CI bearing having a true bore for the displacer cylinder. It runs OK, but I get a few hundred RPMs more with the improved method for making the bearing.

https://www.youtube.com/channel/UCzgMCwQk2JT6uJd57zz2aVg
Ted

 

[anday1]

hi Ted
so drill a hole the use the hole as a datum to then turn OD ? (btw way i have only been machining for 3 months...label printer by trade which are just lathes with ink lol`) i shall try that but i will drill the hole on the mill...better feel i should think. I will also make a power piston in brass. my displacer is 12mm glass which is very light. the adjuster I made was because the drawings I had did not have any of the rods to follow and make.

Thanks for your support on this I was so happy making it and was a little down with the lack of success on making it go...i will make it work though one way or another.

thanks again Ted hope you don't mind me asking more questions in the future

Regards
Andrew

 

[anday1]

just viewed your builds ted they run wonderfully building 1 took me alot of time but 3 my wife said is just showing off hahaha
I am going to try to make this as a winter build this helecopter
http://zeamon.com/wordpress/?p=733

andrew

 

[Technical Ted]

Attached is a set of drawings that includes the missing linkage drawings.

It's hard to tell from that one picture, but it looks like the linkages you made are a little heavier in diameter than design, which, I understand because you had an un-updated copy of the drawings that was missing these linkages. That's added weight that mine interfere with operation.

Also, when you look at the engine from the ends, everything should be in straight alignment. No twisting of components; everything perfectly straight. Also, make sure none of the linkages/components are rubbing on each other or anything else. Everything should be spaced so absolutely no friction is added. All parts should be made to spec and not oversize to minimize weight. Friction is the KILLER with this one!

It doesn't make any difference where you drill the CI bushing if you are going to finish the OD on a mandrel as I suggested. Just make sure you hold it concentrically when setting up in your lathe. I used a collet. If you don't have a collet you'll have to be creative and make sure the mandrel is running perfectly true before finishing the bearing OD.

Feel free to ask questions and I and others will be happy to help all we can.

Ted

 

[anday1]

ted
no need to respond but are you near post code YO42 4ne?

andrew

 

[anday1]

sorry just seen your in NY lol

 

[Ken I]

Anday1 - see also my thread on the Stirling 60 + my revised drawings. Ted was a great help there as well.

Jeroen Jonkman's Sterling 60

I agree with Ted, you can't just drill a hole and get the concentricity you need (see sub link "I Can't Drill Straight)

There is a lot of information traded between members in that thread that you should find useful.

The one tip I can give you is that whatever your concept of "free running" is - it won't be good enough - these things have to be absolutely free running - if spun by hand they should spin 8 to 10 revs and never show the slightest jerkiness or bias in stopping positions (indicating a tight spot).

Regards, Ken

 

[anday1]

many thank ken I will post how I achieved this ...hopefully . for the record I really appreciate your thoughts and time.

 

[Rocket Man]

I have built a lot of sterling engines I have several on YouTube. Friction and mass = weight is the killer. Small engines are the hardest to get them to run they barely have enough power to run themself.

Put Labyrinth seals on the piston, .020" wide .020 deep .125" apart full length of the piston. These act like frictionless piston rings.

Remove all the weight you can from the power pistons and make hollow piston rods.

Temperature difference from hot end to cold end is best about 600°F or more.

Sterling engine is a closed air system there needs to be NO air leaks. Put Labyrinth seals on the crank or the bushings. Clearance of .0005"

Dis similar metals have a different expansion & contraction rate. Piston & cylinder clearance should be .0005" after the engine is warmed up to run temperature.

I build my displacer piston from 3 pieces of round sheet metal attached to the piston rod. Space the pieces so full length is 2" cylinder diameter. Wrap a piece of kitchen aluminum foil around the 3 flat sheet metal washers to form a barrel piston shape this makes an extremely light weight piston. 2 of the 3 piston sheet metal flat washers can be full of large swiss cheese holes to reduce weight. If you can use an aluminum beer can or soft drink can for the displacer piston is saves a lot of work building a piston.

Displacer piston should have .030" clearance when it is all the way down and .030" when it is all the way up.

I build Beta type Stirling engines they run best.

Displacer piston clearance between cylinder wall and piston is tricky to figure out. If displacer piston diameter is too large the piston sucks a vacuum & builds up press on the other end as the engine picks up speed soon it takes too much power to move the piston then RPMs are limited to a low run speed. Small 2" bore engines should run about 1000s RPMs. If space between displace & cylinder is too large then there is not much air movement inside the cylinder this reduces engine power & engine runs slow. I often make several displacer pistons each one being .050" larger than the other then test each displace piston in the engine to see how well it runs. Once I learn the aprox diameter of the displacer piston I build several that are .010" larger than the others then test them this tweaks the engine from best running power & speed. Aluminum soft drink cans & beer cans make excellent displacer pistons you need to bore the cylinder to match the aluminum can.

My piston rods to the crank are I beam shape I cut away all the metal I could. There is no way to type an I beam shape.

NO thick oil on any moving parts. No oil inside the cylinder 400° or hotter oil turns to smoke this produces high air pressure inside the cylinder that causes the engine to stop running.

THIN metal gives the engine a much higher heat transfer rate so engine will run much more efficient and faster RPMs. Try to get .030" metal thickness on the hot end & cold end of the engine. I notice a very big different in my engines if I change metal thickness from .030" to .020"

Here are some of my hot air engines. I lost my YouTube password 10 years ago they have no option to recover password so
I have a terrible time finding my videos. If you clink to see my other engines you will find them. YouTube only lets me see 15 of the 60 videos if I click to see more videos. First video fan makes a low of noise my clearance is too low at the top of the stroke piston hits the top of the engine. I have been wanting to fix that for many years but I have not. FANs run 450 RPM but remove fan blade they run 900 to 1000 RPMs.

 

[mike-oz]

Hope someone is still on this thread. Finally got back to my Stirling 60 after abandoning for some months due to frustration.

Very basic question for this models gurus ..... how have you held the tiny connecting pins in place, particularly when they probably need to be removed and refitted a hundred times for tweaking!
The tiny parts (for my skill & machinery level) have been a real challenge.

Next project will be scaled up x 4, no, make it 10. Just need to increase my overdraft to buy the stock .

Cheers
Mike

 

[Ken I]

Very basic question for this models gurus ..... how have you held the tiny connecting pins in place, particularly when they probably need to be removed and refitted a hundred times for tweaking!
The tiny parts (for my skill & machinery level) have been a real challenge.

This is how I "made" my pins :-

Squeeze end in a precision vice.
You can knock them in and out plenty times - being careful to realign the "square" - when it all works according to plan add a tiny drop of Locktite to the square end - it will wick in and secure the pin. Even then you can still knock it out - clean up with Acetone and repeat.
Working just fine - since the MIG wire is generally toleranced down and I did not have a Ø1,2mm reamer, I just drilled it Ø1.2 and it was fine.

P.S. The drawing is to scale inasmuch as the square is the same cross sectional area as the cylinder.

I see you have looked at my posting elsewhere :-

Jeroen Jonkman's Sterling 60

Go back and look at more recent posts #69 & #71 where I ran into some problems which might also be illuminating.

Regards, Ken I

 

[Technical Ted]

When I made my three engines I made the pins this way. There is a secret to making small diameter pins like these. You turn them from stock well oversize i.e. 1/8" (3mm) diameter and turn them to final size all in one pass. Touch the outside of the stock with a very sharp HSS tool bit and dial in the amount needed. Turn a length using a fine hand feed and measure. Make your adjustment and make you pins. It usually only take one adjustment to get the pin on size. If needed, you can touch them with a fine, small file or emery paper. It's very easy to do. See attached where I took a picture of making the pins for one of my engines on my 13" South Bend lathe. I turned them in a single pass. Once turned and cut to length I upset one end with a pair of pliers. It doesn't take much if the pin is sized close to the hole size. For testing, I simply pushed the pins in, non-upset side first. Once I got things running, I put just a tiny bit of Loctite on the non-upset end. This can easily be removed with heat. During testing the pins stayed put because of the slight press fit from the upset end.

See my three here:

Ted

 

[mike-oz]

Thanks guys I will give them a go!