With the ring grooves narrowing, I am guessing the pistons were used and the flexing of the rings during travel wore the outer section of the ring lands... if you use a section of the ring, can it rock up and down when in the groove? Wondering what the piston measurements are... worn at the skirts? were the pistons tight in the bores?
For your measurements, you note the rings at, "top ring in both pistons was .0632" thick and the middle was .0625" thick.", and, " I measured the slots of a bunch of old Hepolie pistons and they were consistently .0350 to .0360 wide"... should that be 0.063"?
How are the groove depths compared to the depth of the rings?
I'm thinking you are right with new cylinders and old used worn pistons.
I see the HEPOLITE RING PACK NO: R26730 compression rings are
WIDTH: 1/16" (1.588MM)
RADIAL THICKNESS: .124" (3.140MM)
[URL unfurl="true"]https://www.rgmnorton.co.uk/buy/850-piston-ring-set-20-complete_221.htm[/URL]
