Inspired by Click's recent (and epic 31 page) thread. https://www.accessnorton.com/NortonCommando/leak-down-test-dont-laugh.24506/ I've got this '63 Atlas I've been working on for a while now. It runs well enough until it oil fouls the right side cylinder in a couple of miles and I can visually see white/grey smoke from the right side exhaust. Single Monoblock TriSpark in a points body. Issue does not follow plug leads. Head just back from the menders. About 120# compression on both sides and that's with original dished pistons. Rocker flats facing inwards. Verified oil drain passage clear to open timing chest with some carb cleaner and straw. Cylinder marked as +.010 and measurements confirm this. Decent crosshatch pattern still visible. No obvious scoring of the bores. I thought it looked "just fine". I've spent a lot of time chasing this issue. Lots of good practice in removing and installing the head and fitting pushrods. And much like Click, if it's not the head then off with the barrels. The barrel measures up at 2.886 with a couple of 5's measured top and bottom, front to back and side to side, and the cross hatching is still visible. Ring gap is .019 on the right and .020 on the left. Should be between 14 and 9. The pistons are another story. These are original dished pistons marked 24282 (left) and 24283 (right). Stamped as +010. However, they are knurled front and back and I don't think they left the factory this way? The pistons measure up at 2.882 front to back and 2.872 side to side. Honestly, I'm starting to think that someone bored the thing +.010 and knurled the pistons and probably didn't even bother to fit oversized rings. Oh yeah, at some point the pistons had been reversed as there were witness marks in the exhaust pockets. So really what I'm looking for is advise. Try a re-ring or save the money and spend it on the rebore it really wants. If rebore and flat top pistons, what have my fellow Atlas owners done regards balance and fitting a compression plate? This bike's definitely got some interesting stories to tell.