Originally Posted by
Ninja Performance
Common practice, and I have done it for years, is to make that bottom ring on the large side. This way it allows some blow by. If it is too tight not enough blow by get by the ring and it ricochets (ring flutter) right into the top ring and can cause it to break. 25htou/.63mm isn't out of line. I have built them even larger, up to .75mm testing ring gaps on the race car and everything was great.
Think about that gap when the ring in compressed in the bore. AND most of it is covered up by the piston. Only a Smidgen is out in the free air making a gap.
I would not worry about it. It anything, cause I am anal, I would bring the others up closer to the large one to "even" then up. I surely wouldn't buy a ring pack to replace it.
-Chris