Hi, These are File-fit Rings- correct? It sounds as if you have one of 5 issues, most likely listed first.
1) You’ve encountered 2 pairs of Rings that are BOTH are designed for a 0.020-0.030 overbore, not a Stock 4” Bore..
2) The Block has been previously Bored out, and you have Stock 4” Rings...
3) Are you using a Piston to Push the Rings into the Cylinder, ensuring they are sitting in square..?
4) Your Bore is larger than 4” from excessive wear and is “Bellmouthed”...
5) There is a Machining error in a batch from the Manufacturer..
6) Your Measuring Tool is somehow in error.
7) The Bores were excessively Honed by someone, did you lay an old Ring over a new Ring to compare?
Remedy, Calibrate your measurement Tools. Measure your actual Bore with a Bore Dial Indicator, or use a Telescoping Tool, measure that Tool’s with a 3-4”, if needed, move to a 4-5” Micrometer. Make a measurement 1” down from TDC, and 1” down, incrementally to the bottom of the Bore(s). Rotate the Tool 90 Deg. to verify Concentricity. Use only Micrometers that can read into the 10th’s (Lines atop the Micrometer’s barrel, top of Tool). Measure the Piston OD.
Document everything, I’d think you will find your issue once you follow the above.
Oversized Rings & Pistons are available in .020 , .030 , .040 and .060. Older 302’s offered 0.010’s, in the 70’s when Racing restrictions regarding C.I. were really tight. Never seen anything less than 0.020 oversized, and it’s difficult to achieve Cyl. “Clean up” with that, 0.010- Moreso.
I Gap the compression rings at 0.016-0.018 for a Stock 4.00 bore, 0.018-0.020 for a 4.030 bore. Add 0.002-0.004 when boost or nitrous is within the Master plan.
The rings you get should come with directions on how to gap. Does it give information about correct numbers of what you should have, there?
Contrary to typical mindset, a larger second Ring’s gap lessens pressure build up between the two, making it less likely to lift the first ring off the Cylinder Wall. I would still gap the Rings the same, nonetheless..
Good luck!
Cheers!!