One easy way of checking the rotor is to take an ohm reading through the brushes. Remove the wire from one of the brushes spade terminals and touch your ohm meter leads directly to them. You will, however, be getting a reading of the resistance of the brush/slip ring connections also, so keep that in mind. But is a quick way of finding out if you're in the ball park.
I think everyone who depends on their airhead should have a spare rotor on hand for times such as this. It's a whole lot less stressful, and usually cheaper watching for a deal, and no over-night shipping. I've gotten them for twenty or twenty five bucks before.
The rotor won't come off while the stator is in place. So that must come off first. It looks like a simple thing to unbolt the stator and yank it out of there, but there can be problems. First off, the steel of the stator can corrode to the aluminum of the case and won't want to come out. Trying to pry it out can possibly break something, so be careful! It may take a bit of penetrating oil and heat gun to remove it. Also, the stator is just sort of pressed into its aluminum housing and if it wiggles around much, can damage the wires attached to its face or their connections.
Then when installing the stator, be absolutely certain it is lined up with the case and seating properly. If it's not, and the screws are tightened enough, one of the screw tabs can shear off. Don't go there! Take it easy, tighten a little at a time, and if it's not going in evenly, don't expect it'll pop in with a little more force. No. Back it off, get it aligned properly and tighten the three screws each a little at a time. You definitely don't want one side all the way in and then tighten the next...
The rotor has threads in it and there are also threads in the crankshaft where it mounts. The rotor fits on a tapered shaft, and the normal rotor hold-down bolt has threads from the end to half way up its length. Where there are no threads, the bolt has been thinned down to fit inside the threads in the rotor. So when the bolt is tightened, it draws the rotor onto the crankshaft.
The rotor removing tool is just the opposite - it has threads from the head to half way, and then it's skinny to the end. When the bolt is threaded into the rotor, the skinny end pushes on the end of the blind hole in the crank (with the threads) and pushes the rotor off the taper.
These rotors often jump when they break free and fall to the ground. You don't want this to happen! If it hits on the slip ring, it'll mash it and that's not a good thing! Even though it's broken, try to keep from damaging it. Place a box with rags under it, have some way to soften its fall or catch it. I've held onto these things fully expecting I'd be able to hang onto them, and still have them jump off and fall. They're pretty heavy for their size!
Wanted: Dead, smashed, crashed or trashed gauges
BMW GAUGE REPAIRS - TACH*SPEEDO*CLOCK*VOLT METER *PODs & LIGHT BOARD*