Some more photos. I drilled the hole for the tubing alongside the power cylinder, and milled the hole in the cylinder head. The tubing end protrudes slightly into the head.

Then thereīs need to open up the holes in the cylinder support plates for the power cylinder, to create space for the connecting rod. Not much space above the lathe ways, but enough. I drilled it to 20 mm. The piston will be 19 mm (cylinder bore = 19.05mm = 3/4"), so it can enter freely.

And then bored the cylinder to 18,5 mm, and opened it with a 3/4" reamer. I donīt have a drill chuck nearly big enough to hold 19 mm, but the reamer has a centre, so no big problem. You can see thereīs a homemade handle to facilitate turning the mandrel by hand, and slowly feeding with the tailstock, a lot of cutting oil, a spanner holding the reamer from turning, it worked quite well. The bore is straight, uniform in size, and with a rather good surface finish.

I had a slight change of plans. I was intending to use graphite for the power piston, but turning graphite is a messy business. The graphite bar is 20 mm dia, so about 1 mm needs to be turned to dust. Itīs not terribly much, but...
So I was thinking about a Teflon piston. Or rather a Teflon wrapper around an aluminium core. Teflon is also a very low friction material...
I turned an ali bar to 12 mm dia, 23 mm long, and made 10 mm deep hole with M4 thread into one end. And turned a 23 mm stump of Teflon to 19 mm dia, with a 12 mm hole in one end. And pressed the two together. Rummaging in my scrap bin, I found a 70 mm long 6x6 brass bar, and bingo! - a con rod. Unfortunately it was some 4.5 mm short...
I also found a bit of 13 mm bronze bar. I turned the bar to a nicer(?) shape, and milled a 6 mm slot in it.

And soldered the two together.

Now the con rod is long enough. I made a small brass piece, 6 mm dia, with a M4 thread to go into the piston, and a flexible joint with the con rod. So thereīs the power piston as it now stands.

Thereīs a reddish tinge on the Teflon, donīt know why. But itīs really snow white. The bronze "big end" really is rather reddish, clearly different from the brass. I turned two thin grooves in the Teflon, and wound them full of plumberīs Teflon tape. Not that itīs really needed, the piston has a good compression even without it. But it seems to wipe away "something" from the cylinder bore, and it can be easily replaced. And the compression "fine tuned". The stroke is 20 mm, it will be the same also in the displacer cylinder.

The power piston now breathes freely through the tubing, and with a hefty flick of a finger on the flywheel, it turns something like 22-23 revolutions (a bit difficult to count). If you block the tubing, it just bounces back and forth, not even one full rev. So thereīs still some hope - it hasnīt jammed solid yet...
