Oversize rings usually have the oversize etched into the upper face of the ring. Not sure if that's still the case for the L shaped Dykes top ring though.

Oversize Yamaha rings tend to have gaps on the bigger side of spec in my experience.

Thank you Mark

The top keystone ring has an “N25” and 2nd a “2N25” which to me means .25mm OS

So the question to you and the other experts is do I go with a 0.020” end gap, which in the end is a stack up dimensions and tolerances for a properly bored cylinder?

Or could I use a 2nd oversize and file to low end to get “0.012 gap?

Please advise, the goal here is to do this perfectly as possible!

Thank you!
Needed a microscope but they are there!

Recently I checked my CT1-C and the gap was 0.35mm (top limit), the bore measure great and so did the piston.
I offered up a new set of rings and the gap was 0.30mm.
Both sets felt tight in the bore so having asked the question MarkT said the same thing about the gap measuring bigger.
It's all back together and runs fine, so I'm not going to worry too much about the end gap dimension from now on, so long as it's not too much out of spec.

well...piston and bore perfectly within specs, rings are 1st OS with 0.020" gap and even if I wanted to try to fit a 2nd OS set of rings they don't seem to exist on planet Earth

So to the endurologists out there, do I forge ahead with a ring gap that's at the hi limit?

it will run fine like that for a bit but you won't get too many hours on it before low compression and that will result in poor idle and hard starting. don't see why it would hurt anything.

thanks for giving it to me straight

.25mm equates to .030" less end gap. If i am at .020 now, then 2nd OS rings get me to -0.010 meaning that buffing .011 off of each side of ring gap would put me at the ideal 0.012" ring gap

anyone know where i can get a 2nd oversize set of rings?

You'll be fine. A few extra thousandths of ring gap won't hurt anything now or later in my experience. Nor will performance suffer any sooner than it would if you managed to find a set of rings at the lower end of the spec.

thanks
I found a 2nd OS set on eBay for $30 and will fart with this a bit more before taking it any further