looking for advice for a slow running steam engine

[spinningwheels]

I´m new to steam but now i do need a steam engine
It will be a single cilinder dual action bore 60 mm ( 2.36 inch) stroke 120 mm (4.72 inch) should run at around 100 rpm.
I do have a book that gives me some dimentions acording to the bore and stroke.
I will use this to power a steampunk style wheelchair.
When I did my calculations correct I should get around 0,22 HP at 42 psi , that should be enough, don´t want a racer a topspeed of 10 mph will do.
I have a nice piece of bronze for the cilinder, can I use stainless for the piston, Stainless expands under heat a little less than bronze.
I can not find a simple clear drawing of a vertical engine that I just can alter the mesurements in .
what I have is this but that is a bit to basic, what should the diverence be in diameter between the cilinder and piston.
Remco

 

[aonemarine]

If you mean piston to wall clearance I would go with about .003" Also, rings, make sure you use bronze rings on the bronze cylinder...

 

[spinningwheels]

Is there a simple basic build plan for a single cilinder dual action , somewhere to find.
The drawing that I have is a bit to basic to work from
Remco