A friend came by with a non functioning olde 1 hp motor the other day. A
quick check showed no starting circuit (bad cap or bad centrifugal
switch). Pulled the old cap out, it is the old style aluminum case, NO
MARKINGS.

So what size cap to put in?? I just picked a ~200mfd and called it good
but I don't think that is the right answer. So what/how is the cap
sized? Too small a cap and it won't do anything useful. But is bigger
better? Or is the cap matched to the motor in a resonant circuit?

Motor in question is a Westinghouse 1hp 120/240 motor. Judging from the
grease caps, case style, paint color, etc, I'd guess 1940's, maybe early
50's.