Tolerance for gas/steam Engine

[etherist]

What is the standard tolerance for a cylinder bore and piston? The working fluid is steam or compressed air.

 

[Baluncore]

There is no standard for such a broad range of uses.
Minimum clearance will depend on materials and temperatures.
What is gas pressure?
What bore and stroke, at what RPM?
With or without piston rings?
What is the lubrication?
How much blow-by can be tolerated?