I run 0.03" on the top ring, and 0.04" on the bottom.
To prep the piston use some 600, 1000, and 1200 grit paper to polish the dome. This removes the casting or machining marks, and makes it tougher for carbon to stick.
Turn the piston over, and look where the wrist pin goes in the bosses. Drill a 1/8th" hole in each boss, and debur the inside, and chamfer the outside of these holes. This allows oil to get onto the pin, and allows it to "float" correctly.
Finally use the same sandpaper, and sand a 65* bevel all around the skirts of the piston. This allows oil to force between the piston, and cylinder.
Everything else is just removing sharp edges left from machining. Those sharp edges will get hot, and create stress points.
Last thing is install just the piston (no rings) into the bore. You should be able to get a 0.04" feeler gauge between the piston, and cylinder. If not then run a 3 stone hone just a few passes at a time until you can insert the gauge.
If you skip this step, you take the chance of running soft seizes, and galling the piston. Those hones are about 30 bucks at Ace Hardware or most auto-parts, and are a must have.
You will find you have to bend the arms to allow them to fit these small cylinders but it is a non issue.
