LTD Stirling Upgrade, Less Thermally Conductive Displacer Tube Clamping Method.

Intro: LTD Stirling Upgrade, Less Thermally Conductive Displacer Tube Clamping Method.

This is how I replaced the metal clamping bolts on the cheap Stirling engine i bought on eBay, it has dramatically improved the performance of the engine as it now runs at about 180rpm on the laptop PSU where it was previously 60rpm fresh out of the box.

I cut some 5mm x 5mm square strips out of a scrap sheet of 12mm acrylic I had lying around in the shed. I used the band saw to saw the acrylic to size.  I then cut 6 18mm long pieces from the 5 x 5 strip, the pieces where smoothed on some 240 grit sandpaper and i had a go at flame polishing the pieces to make them see through again my attempt was passable but unfortunately i didn't perfect the technique until after i had this project finished.

Once I had the six pieced made I striped the engine down so the mechanisms would not get any more battered than they already are. 

I then removed just one of the clamping bolts and countersunk the holes on both plates so a small brass screw would sit flush with the base.  I tried to steer the countersink towards the edge of the plates to alow me some extra space between the displacer tube and the center of the hole.

I then used CA glue to glue a acrylic block in place at the position of the hole leaving about 1mm of space between the plates.  when the glue had cured i used a 1.5mm drill in a rotary tool to drill the block to accept a screw i drilled the block from each end rather than try to steer it between the 2 holes although one of the holes required me to drill right through from one side only.

Once the hole was drilled in the block i used small brass countersunk screws to secure the plates together, the screws should be short enough as not to touch each other. 

I then repeated the same process on the opposite side of the engine to reduce the chance of any more damage to the displacer tube.  repeat the process until all 6 bolts have been replaced.

Once all bolts have been replaced the engine was reassembled and lubricated, it now has much thermal transfer between the plates other than what the acrylic tube naturally has.

There is an increase of performance of 3 fold as it now runs at approx 180rpm compared to the 60rpm out of the box.

The displacer tube is about shot from me overheating it and also it got a few drops and also fell of the  sub-woofer   when I had the tunes cranked up.  but even after all that abuse this little engine still runs smoothly with just a little bit of oil applied with a fine artist paint brush.

The displacer tube has a number of stress cracks in it, I used CA glue to seal up the worst of then but it don't look to pretty,  I am looking out for a glass jar that is the right size to make a glass displacer tube with. 

I decided to do a test on how long my spirit stove would burn on a full tank of meth with the new flame suppressor fitted.  the result was a staggering 12 hour 50 minutes at an average of 60*c  the engine ran nonstop for the full duration at approx 240 rpm.

Thanks for looking I hope you enjoyed this as much I have had fun doing this.

Comments

[rimar2000]

WOW, what a difference!

You have taken the upper hand (en español: "¡te has llevado el gato al agua!")

[Dr Qui]

Thanks Rimar, this is a big improvement on the engine as it came out of the box.  I can still do a few more simple things to the engine, I would like to put spacers on the cranks to center the piston rods.  I need to make some split washers out of some thin PTFE plastic to go on the cranks.

[scraptopower]

I've been meaning to get one of these cheap engines for some time, I'll have to try this when I get my hands on one. Thanks.

[Dr Qui]

These wee engines are great, the displacer tube is on its last legs because i overcooked it on the basic hotplate, I'm waiting for a bottle cutter to be delivered and will replace it with glass, just hope the displacer will hold out once i go glass and can turn the heat up a bit, well no more than about 100*c. I started on the water cooling system today, I already have the water tank, its base and the cooler made, i need to get a couple of reducers and some pvc tube. will post the results soon.

There a a number of cheap Chinese made gamma Stirling engines  that I have had my eye on on eBay, just waiting till the price reaches its rock bosom before I buy.

All this experimenting is the first stages of building my own engines.