I agree with pete, it will be very hard to get a two piston stirling engine working because it needs very close tolerances and perhaps even rings or leather on the pistons to seal the cylinder walls enough to keep pressure. I doubt even polishing would do it. You'll probably need to drill out the cylinder and lathe the piston to get it close enough tolerance to work. I understand that their metal is very hard too so it will be tough to drill and lathe. Plastic definitely won't work either because of the temperatures. I would love to see what you come up with to resolve it! Also, I see that you don't have a regenerator inline on the tube. Are you planning to add that to make it more efficient?

I was thinking about making one with separated parts so I can polish them before assembling them.

Hi, cool idea, however with moving parts you need quite some clearing if you want metal. It is going to be challenging to build it. best regards, Peter