I'm working on installing a Ford 3G alternator in place of the OEM alternator in my '83 F250 6.9 diesel.
I got a used alternator from a pullapart junkyard and also dissected its wiring harness so I got about 4 feet of heavy copper wire with the fittings that match the upgrade alternator.
This is where my problem started.
Most Ford alternators seem to have the same 15/16" nut holding the pulley on, whether the pulley is for a twin V-belt (like my old F250) or a pulley for a serpentine belt.
I didn't have a 15/16" socket. None of my other wrenches could grasp the nut because of a raised edge on the serpentine pulley on the upgrade alt.
I do have an angle grinder. I used its metal cutting blade to shear off the serpentine pulley's raised edge. Then I could get a 12" crescent wrench onto the flats of the pulley nut.
The nut would not move despite Liquid Wrench, hammering on the wrench's arm, heating the nut and repeating all the steps. The accepted advice on removing this nut is to use an impact wrench - which I don't have & don't expect to get any time soon.
I had read that spare pulley nuts were hard to find, and internet searching yielded little. A website was selling a nut for $12.95 plus shipping, which seemed a bit high since the upgrade alternator only cost $20.00.
I had to drive by the junkyard to buy a 15/16" socket & a chain wrench that I hoped would loosen the nut. I tried using the new tools in the parking lot where I bought them - no deal.
I paid my way back into the JY with my new socket on a 1/2" drive ratchet & a small 2 lb. sledge hammer.
From my previous day's work I knew there were dozens of pulley nuts on the cars & trucks in the JY, and hoped one might be easy to remove since most were secured by belts or rusted rotors.
I walked from junker to junker, applied my socket wrench to every accessible pulley nut, and smacked it with the hammer. Took about 45 seconds per vehicle.
After about 25 attempts I found what I was looking for - the pulley nut gave way & I quickly spun it off.
On my way out of the JY I showed the clerk & paid nothing for it.
Net cost was $1 for admission to the JY.
Hope this helps others in a similar fix.
Postscript: I took my angle grinder to the frozen nut on the upgrade alternator, shaved off chunks of it with a metal cutting blade until very little of the nut remained on the rotor's axle. I heated the nut one last time, then rapped it sharply with a flat ended punch. The nut broke into pieces & fell off the threads.
The chewed-up serpentine pulley remnant easily came off the axle.
I went to Summit Racing & bought a chrome plated double V-belt pulley to put on the upgrade alternator. It should spin the upgrade alternator a bit faster than the larger OEM pulley on the alt on my F250, a good thing. Installed this on my upgrade alt will also save the trouble of removing the OEM pulley and pulley nut. I will remove the OEM alternator & put it on the shelf, undamaged. Cost of the new pulley was about $13.

 

Have since visited another junkyard & quickly found yet another usable alternator pulley nut. I discovered there is more than one type of pulley nut -- all so far are 15/16" across the flats & have the same threading, but some are thicker than others because they are actually hex flange nuts.