[count-your-change]

I'm having trouble visualizing just how a piston can be driven out of a cylinder with nothing touching the cylinder wall to seal the gap between piston and cylinder wall.

Even being a close fit would have too much blow by. So maybe my mental picture of the thing is way off.

Anyway it's an interesting looking machine.

[TigersEye]

The rings seal it. In essence the rings are all that seal any piston and cylinder internal combustion engine.