I might not remember this correctly, but if you plan on dissembling the generator, can't you pull off the back, slide the center off and pop the fan and front cover off as a pair after the nut is removed. I recall opening vise jaws wide enough to accommodate the armature but not the front cover and fan. Stick a piece of wood on the threaded stub and give it a slight whap! Make sure you hold the armature so it doesn't fall.
Does this sound right??
Stuart
