The first complete starter I found is this Gen II out of of a late (post '91) 750. I don't know why the central part is iron-based, instead of aluminum, Perhaps this saves Yamaha fifty cents per bike? Anyhow, you can see how corroded it is. You can see that someone didn't notice the circlip holding on the drive gear and whacked it with a hammer a couple of times. I've already dressed it with a file, and since it doesn't show when assembled. I decided that I didn't need to spend time prettying it up. Next is scrubbing in a solvent bath, then disassembly. Oh yeah: the shaft is seized somewhere inside the motor. We'll find out how.
Some More Pictures
Scrubbing with a soft brush, dish detergent, and water didn't do anything for the exterior. It cleaned the inside okay, but I want this to be a grease-free demo, so I'll be sloshing it about in gasoline. I won't do any blasting as I don't want to pebble the interior. Next is the wire wheel -- we'll see how hard it is to remove rust and bad paint. I might end up blasting the exterior anyhow.
I was surprised to see a four brush plate. According to the "microfiche," the plate with brushes is replaceable as a unit with the positive stud..
I never found a reason for the shaft refusing to turn; everything looks fine. Perhaps a little corrosion was sheared when I hit the shaft with a leather mallet?