Chuck,

I am plowing the same ground. I'm working now on a PM Research boiler for
an old Tiny Power engine. Tiny Power includes a groove for 2 rings. They
imply you can either make CI rings or use teflon tape packed in the groove
for a piston ring. Teflon tape and saturated steam probably will make a
pretty good ring for use on saturated steam. Another approach I have used
on small cylinders, is to make the piston a very close moving fit and cut
some shallow grooves in it to act as "rings" with retained moisture.

Bob Swinney
"Chuck Sherwood" wrote in message
...

I bought two stuart steam engine castings kits at NAMES a couple years
ago. Every so often I get them out and do a little work on them.

I was wondering how much piston/cylinder clearance is required.
The bore is 1 inch and the stroke is 1 inch. The cylinder and piston
are both cast iron and the piston is suppose to have 1 ring.

Should I stick with the CI ring or change to a teflon ring like
PM research uses?

I hope to build a PM Research kit and run them on live steam but
I suspect they will run on compressed air most of the time.

chuck