Here is an interesting hypothetical...My 1980 R100 began to smoke quite a bit from the right cylinder with relatively sudden onset. (Mileage 65K)
I pulled the head and cylinder expecting to find a broken ring. All rings fine, but I did notice that the bottom (oil) ring' opening was straight down at 6PM position.
The next ring was at approximately 5:20. The top compression ring was around 10:00.
I have heard that rings tend to rotate around the piston after a fashion...might they have rotated so that the two lower rings were both open in the same area? If so, would this cause oil to blow past them and overwhelm the top ring, hence the oil burning?? The spark plug on that side is a nice tan color, so the oil burning hasn't been going for long.
What are your thoughts??
PS... I may re ring it anyway, but may not if it was a 'ring rotation' issue. everything else is in very fine appearance...valves, piston skirt, cylinder walls ...meaning no recession, scoring etc