As the piston moves up and down in the cylinder it also moves the piston rings up and down in the grooves. With the rings moving up and down it gradually increases the side clearence. Material is taken off from both the piston groove and the ring.
assuming that you have new cylinder liners and pistons or old pistons with good ring groove conditions, piston rings come with the correct/specified clearance when bought new.
bumping clearance is the clearance between piston and head ,piston and crank endside
most auto mechanic preferred .002 clearance from piston skirt to sleeve
the pistons most likely have zero clearance in the between the piston heads and the valves. When the timing goes out on a vehicle with zero clearance, the piston heads hit the valve heads, thereby bending the valve stems.
one ring per piston, the pistons have a groove in it where the ring fits on.
Piston ring gap.
Well...... you need A LITTLE bit of clearance for the gas mixture to lubricate the piston and cylinder. Plus your piston expands when it gets hot.
Piston is the device with a cup like shape that fit completely in the Cylinder.
The volume between the engine head and piston when the piston is in the head dead center piston R - is expressed in cubic inches
wrist pin to crown . the area of cylinder wall the piston travels ,shirt to upper ring groove