Michael Koblic wrote:

1) Are sleeve bearings usual in electric motors or is this some old, cheap
model?

Sleeve bearings are common in older motors. Like Roy said, a sleeve
bearing has some advantages over a rolling element bearing. They take
high loads better. They are also quieter as their stiffness doesn't vary
with position. Quite often sleeve bearings are more expensive than
rolling element bearings.

2) Are shafts in such motor usually machined in one piece or is a 3/4" shaft
rammed into a mandrel to hold the rotor? In spite copious cleaning I cannot
tell for sure.

Probably there is a shaft of 3/4" diameter (which is of a slightly
larger diameter in the centre; you are unlikely to be able to remove
this without turning down the shaft) which is somehow attached to the
rotor. The three methods I've seen for attachment a (i) small splines
on the shaft (the shaft is then pressed through an undersize hole in the
laminations), (ii) a key and keyway, and (iii) welding. Depending on the
method of attachment, you may be able to remove the rotor, but it
probably won't be easy. The rotor has to stay firmly and reliably
attached to the shaft in service.

3) I am puzzled at the inability to shift the rotor. If the sledge hammer
did not do the job is a gear puller (or some other gizmo) likely to succeed
(as well as protect the shaft, of course)?

Unless you have a very strong gear puller, probably not. A good strong
puller, like some of the larger Gedore/Baldur models, might be able to
move it. But a cheap gear puller won't.

4) Am I missing some method by which the rotor is held onto the shaft
rendering the sledge hammer ineffective?

It sounds like your rotor is secured by a key. If it's a taper key, this
is probably why you can't remove the rotor. Taper keys are designed to
jam tight. If it's a parallel key, there may be a threaded hole for a
grubscrew which holds the key in place. If so, you need to remove the
grubscrew. Rust may also be jamming the rotor in place.

If it's a taper key, I find the best way to remove them is using a
strong gear puller. You need a puller capable of exerting several tons
of force. Also, if you have to pull the rotor in the direction which
tends to push the taper key further in, put a piece of metal under the
head of the taper key to stop it sliding further in and jamming the
rotor on tighter.

Good luck!

Best wishes,

Chris