On a conventional motor where the main bearings
are "fixed", I presume both bearings would have
been "line reamed" together at the factory.
Any inaccuracies in the boring of the new bushings
or in the stamped halves of the crankcase, would
cause binding. The bushing "cases" or "cartridges"
weren’t all that accurate on the OD where they
chucked into the lathe, so I could have a combination
of problems.
I would have loved to been a mouse in the corner at the Thor
factory to see what they did when assembling the
crankcase to assure everything turned freely!
Mumbles, I like your idea about seating my new rings with fogging oil
and a lathe, although I may find it easier to use a drill.