painting an engine internally started in the '60's. back in the day we did it not so much for oil drainback but to seal the casting from silicon/sand and who knows what from breaking loose during thermal cycles. a lot of racers were using green blocks back then. back then there wasn't any thermal cleaning. everything was a hot tank and the iron had a dirty texture/light surface rusting. we also used the rustoleum damp proof red primer in a can and brushed it on to seal everything. this paint had lead in it so it's no longer available.