Excellent video. Fixing buy a bbr big bore myself for my childhood dirtbike. Got it new in 1992 figured it was time for a refresh. Starts first kick still but smokes like a freight train
There's only 2 ways oil can get into the combustion chamber, rings or valve guide seals. So be sure to replace the seals and check the ring fit in the new cylinder before tearing down your motor. Cheers.