A piston ring made for a particular cylinder bore, when in a "True" position as reached by using the piston to locate it, will have no gap between the outer surface of the ring and the cylinder wall at any point. If there as a gap either the ring is not properly machined, or the cylinder bore is out of round. No exceptions, this is the way it is.

If the cylinder bore is true and you have an air gap then most likely the ring manufacturer has used a single base stock for his rings and gapped it differently for the over bored cylinder. Sad to say, but some of the less expensive (and lower quality) makers do this.

And to the gentleman who mentioned short ring life in the ambulances, it's more probably due to over cooling than the extended idling itself. tell the head wrench at the shop to put the thermostats back in, use clutch fans, or both, his problem will most likely go away.

Finally, the ring will seat in the first few seconds or minutes of running, and a high initial load helps this a lot. Full break-in can still take several hours of running, but the ring seating is almost immediate.

Bill.