Hehe, yep must remove ring bore wear lips or traps ring in bore.
I went through ring issues last spring, Trixie smoking and head gasket blow by after like 5 miles of new engine running. I'd found .022 to .024" gaps, about twice the size of normal, so of course almost every one with long seasoned expertise reflexly responded that - ole hobot was a stupid shade tree that screwed up by not measuring gap before install like every proper mechanic would do. I had to assume they were right - UNTIL - my bud Wes found the same over size gaps with smoking blowby at like 7-8,000 miles [~ 1 yr of rides].
Wes a is proper mechanic and measured initial gap as correct. Deeper digging like the article above plus even more informative ones plus comparing our notes revealed the source of the ring wear and why big gaps don't cause the smoke or case blowby. Wes's intact KN Miki filter and my Amal carb boot cracks were letting in too much Grit to live with long so caused the OD of rings to wear and open gaps, but it was the **rounded upper edge** of the ring wear that was failing to seal letting pressure by - Not The Worn Gap size. Wes now has second foam layer over his KN and I have trimmed the booties to seal again.
Comstock and Canaga told me-us in Trixie ring thread that its long standard practice to put in one size bigger OD ring to take up the bore wear to save old pistons or remaining bore and just file gap open enough to tolerate the heat expected.
Btw our ring gaps were found still staggered, so my impression now is that Norton rings don't rotation to matter a whitworth, either because they rotate so fast they don't align for long or they don't hardly rotate so stay staggered.
Oh yeah the slightly bigger 2nd ring gap idea is to avoid equalizing combustion pressure between ring to keep the top ring pressed down in piston groove and outward into bore.
So my hobot summary - there should be no need to measure ring gap if piston and bore are within the nominal re-bore sizes, then off the shelf out the box ring gaps will be correct, as it has on me and Wes's almost yearly ring jobs.
