Low viscosity oil is a big mistake on a stovebolt- - - -they just were not designed to run that stuff and you'll have numerous knocks, rattles and leaks. While it might be possible to tighten up the clearances enough to run something like 5W-30, it would take a major redesign of everything including having hypereutectic pistons custom made and figuring out some way to reduce the clearance on rocker arms, cam bearings, and a lot of other places to less than half their original specifications. What's wrong with running the 30 weight oil the engine was designed to use?
Jerry
