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Hello all, I have been bitten by the stirling engine bug.I have built a walking beam engine so i thought I would have a go at a chenapan model. At this time I am having problems as it refuses to run, I am about to give the power piston a little more clearance and see how that goes it has .002 inch now any ideas would be good thanks

We can't offer much help unless we have a little more information. The two biggest problems with engines that won't run is friction and leaks. Balance problems probably place a close third. Then there is the old problem of not having clear plans and putting something together in a unique fashion that doesn't produce power.

If you can post a picture or a video and describe what you are seeing when you try to run it, then you will probably get lots of free advice.

G,day all, just had slight set back when the test tube I was useing as the displacer cylnder cracked but I am still pressing on.The engine is in bits now so I thought I would run some numbers past you and see what you think.
displacer is 21.33mm in dia the bore is 22.2 mm dia the stroke is 26mm long
piston 14.69mm dia 19mm long the cylnder is 14.83 dia and has a 20mm stroke
By giving the piston more clearence made no difference at all.
again any help most welcome.

.002" is a fairly large clearance om a small motor, the piston should just slide through under its own weight with the cylinder open, and if you close the end the piston should stop. If the clearance is too large, a leather cup seal ( like the piston in a bike pump), on the piston is a way of over coming the problem. Ian S C

I made another displacer tube it has .020 overall clearence on the sides and .040 clearence on each end.When you disconnect the the power piston from the main axle and move the power piston you can feel the suction or pressure, it has .0015 clearence. If you reconnect the power piston and heat the displacer and move the displacer the power piston will move slightly does sound right? When you run either the power piston or the displacer by themselves they run for about 8-10 reves. I am makeing the displacer and power piston from ally and stainless steel cylinder and ally piston could this be too heavy? this is where I found the the drawings I used.http://www.stirlingengine.fr/achievements.php#fernand any ideas welcome.

dicko55, the aluminium piston if made hollow would not be too heavy, but aluminium has high friction, and a cast iron piston made as light as possible(it won't be noticably heaver than the aluminium one), makes an excelent piston, brass or bronze is good, and graphite is concidered the best(I'v never used it myself). I have used aluminium with a carbon impregnated teflon skirt over the top of it.
I think the clearance on the sides of the displacer are maybe a bit close, you could quite easily go to .060 in the gap, Mine are sometimes quite a bit more. I found that on one motor the displacer at certain revs and load oscillated, and because it had about .040" clearance, it rattled against the displacer cylinder, I cured it by reducing the diameter of the displacer. The stainless for the displacer should be no more than about .020" thick, if you can get thinner, go for it. You can braze the hot end in, or TIG weld it. The cold end is best made of aluminium, and can be glued in. Ian S C

dicko55 wrote:I made another displacer tube it has .020 overall clearence on the sides and .040 clearence on each end...... If you reconnect the power piston and heat the displacer and move the displacer the power piston will move slightly does sound right? When you run either the power piston or the displacer by themselves they run for about 8-10 reves. I am makeing the displacer and power piston from ally and stainless steel cylinder and ally piston could this be too heavy? this is where I found the the drawings I used.http://www.stirlingengine.fr/achievements.php#fernand any ideas welcome.

I see that engine. Your power piston and material for both cylinders are fine. Your clearances for the displacer are not. Your displacer is rubbing the cylinder wall. You will (may) see marks on the displacer. You can hear it by moving the displacer pushrod in and out by hand and also rotating the pushrod with your ear to the hot cap. Increase the clearance here. Your end clearance of .040 is way too close. You may be bumping the displacer nose into the hot cap. Try at least 3/8 inch. having some contant dead space for the fluid to absorb the heat input. Spinning flywheel and getting 8-10 spins is not conclusive that the displacer is running straight and parallel to inner hot cyl. bore. Things we can't see but the engine detects seem to wrap around clearance in both leakage and friction issues.

Hi there,

Really interested to know how you're getting on with this as I have those plans and I'm planning on making a start on them soon. I'm a (supposed) Mechanical design engineer so I've modelled the parts up with solidworks 1st to check clearances and the running of the mechanisms. However the plans sorely lack tolerance detail. I'll be starting on the 2D schematic drawings as soon as I know the materials best used for the cylinders and pistons as well as their tolerances (I don't paln on using the suggested test tubes). I'll then be putting a full set of manufacturing and assembly drawings freely on the net for all hobby machinists to have a go at... Unfortunately Chenapans details are not exactly..... Well to put it bluntly I'm better at draughting.

My girlfriend happens to be a french translator (convenient for me) and she's in the middle of translating the instructions as well.

I have made some small changes whilst modelling, the original plans seem to use quite a lot of adhesives so I've taken that away and replaced it with mechanical fittings and the idea of using loctite instead. I've also opened up some of the holes and plan to use IGUS bushes in the moving sections to keep friction down.

I'll be posting a large selection of images (from the model) online tomorrow so all help will be greatly appreciated and hopefully will benefit some more people in the future.

cschwartz106 I agree with you about the drawings and the tuts, even after I got them translated they were a bit of a struggle although, it said in the tuts this is a test of patience. My engine still won't run I'm trying a smaller displacer tube and giving the end space 3/8 end clearence this should bring it back to the syringe size.This is bit of information lacking, another is the fly wheel is made in two pieces when I made mine it leapt slightly. The next one I made I made all in one piece, a much better result. When I get my engine to run I will certainly be offrering any help I can with sizes etc. Just a thought , is it possible to have too large a displacer meaning you get too much expanded air and the fly wheel can't push past it? The first battle may be lost but the war is far from over

As I was modelling it I did realise the flywheel would be better as 1 part rather than 2. Did you use brass where he's used it originally? I have easy access to ally, MS and SS but brass is a bit rarer. Going by what other people have said on these forums I'm assuming you need a close fit between piston and clinder but as frictionless as possible. I was hoping doing a machinery's hand book ISO limit fit would suffice i.e. H7/g6 - probably a bit sloppier than that though.

I did use brass on the fly wheel, but I have seen them made out of aluminium. My power piston has a 0.0015 inch clearance, and cschwartz106's tolerances seem similar.

Due to work committments I may not be able to get back to you at the moment.

The battle still rages!!

Back again, I have recieved some good information from my daughter regarding my little engine. She sugested that the aluminium might be spreading the heat too quickly, so I found two test tubes to work with the first I probably heated it too quickly and it broke at the end.The second one I gave it about 1/4 " end clearence and heated it slowly and guess what my little engine runs.The thing that I found interesting is the displacer has about .060'"clearence the specs sugest .030", the main thing is it runs.There is nothing better than the sound of a running engine.The war is over till the next project, thanks to all for your input.

That daughter of yours is not dumb is she, is she going to go into engineering? Congratulations on getting your motor running. Ian S C

Yes I think she is pretty clever, she is a mechanical engineer. Thanks for the congratulations, it was great to build an engine and see it run. Now onward towards the next project.

I did'nt think of her being of that sort of age, I was thinking back to when a nephew of mine started making similar sugestions about 20 years ago, when he was 10, at school he was concidered a bit slow, but once in the workshop that was a different matter. He's now a cabenet maker, fitting out luxury yatchs.
Ian S C