Hi Steve,
I went through the headache of finding rings recently for my Flash. It has new bores at 70.5mm, but were glazed with only 40 miles running due to issues I have detailed elsewhere on the Forum (Smoking), so replaced the rings as a precaution. The pistons were 25yo Hepolites, so presumably English-made.
I purchased a set of Gandini rings locally with the specification on the package blotted out due to the poor condition of the package. The ring measurements did not match the old Hepolite rings.
I finally purchased a set of AE Hepolite rings from SRM, being fairly confident that they know their stuff.
The AE's did match the original spec and also my old rings, although the AE's do have more Back clearance - along the lines that Hastings recommend. I have attached the measurements, which also show clearances both either top/bottom of the ring and back clearance.
If you are matching new rings to existing pistons, the only advice I can give is to
make sure the supplier is prepared to take them out of the package and measure both the thickness and depth before parting with your hard-earned. After trying this with Draganfly for two weeks, I gave up.!
They did eventually do so, but by then I had already ordered from SRM. Draganfly's new Gandini ring spec did also match.
After getting the head done up, de-glazed the bores and fitted the new rings, I have re-assembled and run the bike fairly hard but variable for 5 miles - still some smoke and oil on left cylinder.
Given the issues I found with the engine, I was just too smuggly confident to check the breather system and a few other smoke sources. Those little jobs will be next before I do serious miles on it. Geez it ran like stink though.!!
Col