Does anyone know how accurate the base or mounting bolts are located on an electric motor in regards to the centerline of the motor shaft? Not concerned with the elevation centerline, not sure of the proper term but the left to right parallelism if that makes sense. The ones I'm currently dealing with are 25 HP. Good quality name brand. (Can't recall off the top of my head) Not being an electrician but these appear to be well built American made. I can only assume the parallelism must be close because the base bolts are are close to size telling me that there is enough wiggle room to do a precision alignment with the pump in this case. This particular motor uses a three piece drive coupler, two hubs, and a center shaft with flex plates.
Like any other manufactured item, the tolerances are called-out,
right on the print. Which means.. you need to know the makers and at least the "family" of each motor so you can go and GET the matching print and/or specifications in a published table.
"Foot" mounts, as others have said, are expected to be shifted left-right / in-out, and shimmed up-down at the time of installation.
"Face" mounts are made to a closer fit, those with a locating ring ledge most of all. Even so, just "how" close is, again, in the callouts on the maker's drawings or tabular published specs.
Many motors are "both", of course.
Industry standards for "frame" types differ, US or Euro/IEC, practice, but standards they are. No mystery about the specs. Only about "which motor" have we, here?
Absent data plates, yah just have to do the detective work on an unknown motor to find what it "seems to be" at least as far as frame type or equivalent so as to find what is already published.