problem with power piston

[antidartan]

I have a slightly larger version of the tin can engine. When I move the displacer up and down after heating it, the power piston only sucks in. What would cause it to not also push out. Every thing is working freely.

Thanks
Antidartan

[Stevedigiboy]

From my experiment with pressure sounds like a leak maybe. I'm using graphite with possible exact gap auto shaped upper teflon ring, brass core guide with disp rod and dual heinrici style pp crank arms, I have isolated the top from a 750f heat test with no change over 1hr on burner air cooled.
Steve
pics?