Re: Piston Stuck
Sounds to me like the ring rotated so the pin wasn't at the gap anymore, You'll feel that installing the cylinder because it'll stop dead and not go down any further. If you can't get the jug to go down over the piston with gentle hand force, it's time to stop and see where the rings are.
I can agree with the carbon build up theory too if the engine has been run for a good amount of time and the best way to clean the ringlands is with a section of broken ring as a scraping tool, then gently scrape it out, if the carbon is really stubborn, get a gallon of Berryman B9 Chem Dip at an auto parts store and soak it for about an hour. I've used the same gallon of B9 for almost 6 years as it's one of the best carb cleaning dips out there, and it lasts and lasts. After a good soak in the dip the carbon will still be there but will be loose enough to clean off easily, and it'll clean out a gummed carb like new easily if you ever let the bike sit too long and forgot to drain the carb so if you do buy the stuff it won't go to waste...
You can run on one ring while waiting on parts as long as the cylinder bore isn't scratched, I've done it too... These rings do have a lot of end gap tho so you may or may not experience a power loss, mine ran fine on top but not so fine at low rpm on the single ring.