On Monday, August 1, 2011 10:22:23 PM UTC-4, Christopher Tidy wrote:
wrote:
[about a plastic piston]

I have actually been told ... that it was thermally moulded, that it was
special nylon with a low coefficient of friction, that it was
hygroscopic, and lastly that it was glass-filled nylon.

Well, 'nylon' means polyamide plastic, glass-filled means it was
probably thermally molded to a precise size (that's the benefit of the glass
filler, that the size is stable).

I suppose you could burn a sliver to see if it has the ammonia-like
smell of polyamide. It's more likely that a low-friction plastic
(Delrin aka acetal) would be used, rather than polyamide, for a sliding part.