A little extra info for the winter months' thinkers:
On mine, as an example of "what to do when the crank wears down", I just bought the next size down from the original sizes. I had replaced the bearings several times before 1980 (due to roadrace injuries, mostly), but always with the same size as stock. Now, 120,000+ miles later, the crank's journals are worn to the point where they are nearly .0008" undersize from their original size, just from the miles. They are still round (this would not necessarily be true of the rod journals!), so I have gone "down" 1 step for this next upcoming rebuild. Honda's bearing came in those useful .0004" increments, and I could go 2 sizes down, but have learned from experience that an extra 1/2 thou crank clearance makes for a happier engine on a real hot day in city traffic. (For roadracing, I'd jump down 2 increments, though, to keep the crank accurate at hi RPM.)
Rod journals: they wear more on the "power stroke" side, i.e., the side that faces up the cylinder when the piston is near TDC. This is true because this is the side that sees the push from the piston on power stroke. The rod journal wears a little less on the "other side", from pushing up during the exhaust stroke, but the sum of the wear is a slight oval shape on the journal, about .0013" on my worst one last year. It's not practical to just undersize the rod bearings like the crank, because the "wide" part of the oval then becomes too tight. Rod journals usually need to be repolished down to round again in hi-mileage situations like mine.
All of this extra clearance in the crank wouldn't be a problem IF new oil pumps (or hi-flo Yoshimura pumps) were still available, because the top end of the engine would not starve for oil if a hi-flo pump could be plunked into place. But, as the bottom end's clearances (and resulting leakages) increase, the top end gets less flow. Going to a heavier oil base (20w-something instead of 10w-something) helps because the higher viscosity makes the worn pump move more oil flow again. There is a point where even this improvement is not enough (mine is there, now), and the top end does not get enough flow at low engine speeds (mine: 2500 RPM on a 100 degree day will run it pretty dry), and the overall pressure drops a bit, too. All this signals the need for new bearings.
I just bought some used oil pumps: I'm going to attempt some rebuilding to see how it goes. I sure wish I'd bought some of those Yosh hi-flo pumps back then.....
