23-09-2021, 09:09 AM
Two oil scraper rings with the lower one at the bottom of the skirt was the norm 50+ years ago even on seriously big engines of 16" bore or more. However it was found that if the lower scraper ring was too efficient it resulted in piston seizure due to oil starvation of the skirt so flats were cut on the running face which worked well till the ring wore down and he flats disappeared so notches were cut in the running face. Then in the 1970s the lower scraper ring was moved to above the gudgeon pin which resolved the problem giving low oil consumption without piston seizure.