Thanks for the replies

.
Piston/cylinder fitting is in progress. Although 3/4 is done, it's quite tedious job to do, as I have to do it manually. I tried using lathe for that, but piston gets too easily stuck in the cylinder. So tight, that it has to be hammered out.
I really don't prefer to do that. That's the reason, why I do the job manually.
One may ask: "why don't you use o-rings?". During the process, I have indeed looked for an easier way to make tight cylinder/piston fitting.
I have read about successful use of Viton as piston ring(s). Viton is available here, but it's rather expensive.
Anyway, I have enough ptfe(teflon) to make o-rings, as an alternative, as it stands heat, and doesn't require lubrication.