How tight is the fit between the shaft and inner race of the lower guide rolling element bearing on a vertical hollow shaft motor driving a vertical turbine pump? Is it comparable to the interference fit on a similar sized / speed horizontal solid shaft machine?
What about vertical hollow shafts that use a guide bushing? Similar to its horizontal cousins?
And lastly, if there are no clues about which lower guide bearing a particular motor contains, are there any rules of thumb about determining that?

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How tight is the fit between the shaft and inner race of the lower guide rolling element bearing on a vertical hollow shaft motor driving a vertical turbine pump? Is it comparable to the interference fit on a similar sized / speed horizontal solid shaft machine?

Yes, intereference fit is common.

If the top has angular contact ball bearing, the bottom would most likely have ball bearing. A kingsbury thrust, or other pad type bearing on the top often leads to bushing/babbit guide on the bottom.
It's been awhile since I have been in the motor repair business, but I don't think has changed much.
Call your local motor repair shop if you have one. They can be very helpful.