1985 442 78 Amp 12SI Alternator Restoration
- Thread starter 69hurstolds
- Start date
Just wanted to add to the data sheet here in case anyone loses a collar/spacer doing a job like this and needs to make one or in the event they forget which goes where. I measured the spacers for a couple of the 12SI alternators. The outer 2 checked out as 0.998" nominal OD. (25.4 mm) For the single V-type pulley, the pulley end collar is 0.3975" (10 mm) thick x 0.669" ID (17.04 mm) nominal size. I have one as 0.3965 and another as 0.3985. Split the difference. The stack spacer behind the pulley spacer (still outside) is 0.279" nominal (7.1mm) x 0.674" ID. This smaller one goes on the outside first, then the pulley spacer, then the pulley and nut/washer.
The inner collar which slides on the shaft and sits next to the rotor windings (can't see it once the alternator is together) goes on before installing the rotor through the front bearing. It's smaller OD, at 0.904" (22.94 mm) x 0.373" thick (9.46 mm). Still has a 17.01 mm diameter to slip over the 17mm rotor shaft.
Basically, starting from the rotor, medium (p/n 1975350), thinnest (p/n 1984476), and fattest (p/n 1978064) next to the pulley. The one next to the rotor also has the smallest OD. I've seen them with the same basic sizes with all sorts of different part numbers, but you can usually find them by size. I guess it doesn't really make much difference in the outer 2 spacers which goes where, but I'm putting it back together like Delco built it. Skinny in the middle.
I edited the CSM drawing to show the sizes. Keep in mind these are nominal sizes for a single V-belt pulley, such as on the 307 V8 cars, and MOST G-bodies that I can see. The only spacer that seems to change part numbers is the skinny middle one. Every now and again I see the rotor (inside) spacer as 1986000 which is 9.5mm in length and 22.23 mm OD, but still in the same ball park as the 1975350. Meaning they're not exact from part to part. The idea is a smooth slip fit over the rotor shaft without binding but not sloppy either. Whenever you take one of these apart, it's probably best NOT to lose the spacers.
The inner collar which slides on the shaft and sits next to the rotor windings (can't see it once the alternator is together) goes on before installing the rotor through the front bearing. It's smaller OD, at 0.904" (22.94 mm) x 0.373" thick (9.46 mm). Still has a 17.01 mm diameter to slip over the 17mm rotor shaft.
Basically, starting from the rotor, medium (p/n 1975350), thinnest (p/n 1984476), and fattest (p/n 1978064) next to the pulley. The one next to the rotor also has the smallest OD. I've seen them with the same basic sizes with all sorts of different part numbers, but you can usually find them by size. I guess it doesn't really make much difference in the outer 2 spacers which goes where, but I'm putting it back together like Delco built it. Skinny in the middle.
I edited the CSM drawing to show the sizes. Keep in mind these are nominal sizes for a single V-belt pulley, such as on the 307 V8 cars, and MOST G-bodies that I can see. The only spacer that seems to change part numbers is the skinny middle one. Every now and again I see the rotor (inside) spacer as 1986000 which is 9.5mm in length and 22.23 mm OD, but still in the same ball park as the 1975350. Meaning they're not exact from part to part. The idea is a smooth slip fit over the rotor shaft without binding but not sloppy either. Whenever you take one of these apart, it's probably best NOT to lose the spacers.
True. Factory and GM replacement stators don't have any insulation on the terminals or wire on the terminal ends. You need to do that yourself if you want it done. Some aftermarket units, like in your picture, actually do have sleeves or other protection from grounding. Not a horrible idea.
I thought the alternator was lost somewhere. 
Hadn't heard from the guy I sent it to for refinishing the hardware and shells in a while. He is considered one of the best in the business for refurbishing alternators and starters and junk. So I tapped his shoulder last night.
He sent some pics today. He's waiting for the plater to get done with the bright zinc bits and then it's pay the final bill and I get my junk back. Apparently the plater guy's nickname must be "Sloth". If not, it should be. Must work for the USPS.
I'm also getting the restamp of the "AR" on it as per original. It was so dirty when I took it off I glanced to see if it had a stamp and missed it (it's at the bottom inside when mounted on the car so you can't really see it anyway). When the guy was cleaning it he alerted me to the stamping and asked if I wanted him to redo the stamp. Well, sure. That's how it came.
Only issue is that the font he used for the stamp is incorrect Helvetica. Oh, well. Nobody's going to see it anyway. I might figure out how to rub it off and restamp it with the correct font stamp, which is a slightly narrowed Arial Black. Or maybe not.
The alternator looks a little better than it shows here. It's a bit brighter and shinier than the pics show. But it looks so much better than when I took it off.
These are gray phosphate.
Hey look, an adjuster screw stop being refinished in black oxide. rfpowerdude will want to steal it. I got other bolts I tossed in too for refinishing.
Original and a spare pulley and nut.
AR stamp
Alternator bracket
Hadn't heard from the guy I sent it to for refinishing the hardware and shells in a while. He is considered one of the best in the business for refurbishing alternators and starters and junk. So I tapped his shoulder last night.He sent some pics today. He's waiting for the plater to get done with the bright zinc bits and then it's pay the final bill and I get my junk back. Apparently the plater guy's nickname must be "Sloth". If not, it should be. Must work for the USPS.
I'm also getting the restamp of the "AR" on it as per original. It was so dirty when I took it off I glanced to see if it had a stamp and missed it (it's at the bottom inside when mounted on the car so you can't really see it anyway). When the guy was cleaning it he alerted me to the stamping and asked if I wanted him to redo the stamp. Well, sure. That's how it came.
Only issue is that the font he used for the stamp is incorrect Helvetica. Oh, well. Nobody's going to see it anyway. I might figure out how to rub it off and restamp it with the correct font stamp, which is a slightly narrowed Arial Black. Or maybe not.
The alternator looks a little better than it shows here. It's a bit brighter and shinier than the pics show. But it looks so much better than when I took it off.
These are gray phosphate.
Hey look, an adjuster screw stop being refinished in black oxide. rfpowerdude will want to steal it. I got other bolts I tossed in too for refinishing.
Original and a spare pulley and nut.
AR stamp
Alternator bracket
From what I understand of the process as described to me: The aluminum parts were ash blasted or some stupid stuff like that. A very very light abrasive medium. Then, the aluminum was plated with some sort of aluminized coating which afterwards, doesn't have much shine to it. Then, it gets a light spritzing of some sort of semi-flat clear to give it a basic glimmer. That's all I know. I might be off on that, but that's my interpretation.
I'm not sure how ACDelco used to do it, but they managed to clean the aluminum to give it a new look to it. So from that perspective, I know it CAN be done, but what process? Cost-effectiveness, etc.?
I don't really know for sure. I haven't got them in hand yet. They're in "plater's jail" for some friggin' reason, waiting on the bright zinc parts to be redone.
I'm not in any real hurry, but I also didn't think it would take THIS long to still not have my sh*t back.
That reminds me, I think I'm going to shoot an email that way and see what's up with that...
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