OK, so outboards use needle roller bearings on the big & little ends, why don't 4 stroke motors use roller bearings on the crank & cams? I would have thought they'd have less friction. I did think that perhaps the combustion loads might disintegrate the roller bearings - but outboards survive without too much trouble?
Didn't bugatti try it on a race motor many many years ago?

Didn't bugatti try it on a race motor many many years ago?