Stirling Engine Project Status

I now have the piston/cylinder assembly ready for testing. On Friday I found a distributer of plastic bags near where I work and got 3 samples, 3" x 6" flat polyethylene bags:
1- 2 mil thick
1- 4 mils thick
1- 6 mils thick.

The actual size of the bags varied and the thin one split down the side as I tried to fit if over the piston. The 4 mil bag was oversize so while it easily fit over the piston, it was too loose to properly fit into the cylinder with creating creases.

The 6 mill bag was tight and had to be stretched over the piston. Get it into the cylinder was easy, but getting it to fold back over the piston was tough. The final step of stretching it over the outside of the cylinder took hours. I think I have a better technique now, but with the bag already stretched out it may be just easier.

The bag got damaged near the sealed end of the bag, so I had to patch it with scotch tape.

This bag seems too thick, because it would rather slide in cylinder rather then roll. It seems to work OK when under pressure, but the seal is still not good. It could be more leaks through the bag or the top cylinder to head seal.

Conclusion: The current bag is both the wrong material and not the right size. But it does seem like it could work. Still need to find a seamless 2" diameter Nylon bag, which would 3" across when flat. I man need to do some custom reforming of the bag to get to be easier to install.