I find the hardest part of making a Stirling Engine, when you have not got a metal lathe, is making the power piston. While trying to find something to use for a power piston, I found that the diameter of a one pence piece was just a little bigger then the diameter of 20m plumbers copper pipe. Here is a power piston I came up with, that uses two one pence pieces and a bolt with three nuts. Total cost - around three pence! It is easy and cheap to make, and more importantly, it work very well.
It is on my Hints and Tips page
Roy
http://homepage.ntlworld.com/sheepdog1951/
Power Piston
Power Piston
If you are not part of the solution; you are part of the problem.
I used the Haigh Piston. I used the same size brass pipe for my mould, as the cylinder; 2 crimp connectors set in the matrix for the piston pin(plastic removed). Then I knocked it out of it's mould and turned it down on the drill press for a great fit. I used sanding cloth plumbers use for dressing-up joints before soldering, for the "turning process". On the bed of the drill press, I installed a point off of a set of tie tongs used at the railway, and then drove a dowel through a wooden thread spool, applied two sided tape to the face, and used that for a face plate.(chuck the dowel in the drill).I stuck the top of the piston to this assembly, then lowered it onto the point, locked it down and did my turning. Kinda like a vertical lathe I 'spose lol. Worked very well. Belt sand the top of the piston BEFORE you take it out of your mould. As you sand, you'll see you can go by the amount of material removed evenly by the edge of the mould itself.