12si pulley offset

Joined
Sep 4, 2021
Messages
22
Location
riyadh
78 with 2f, I'm switching to a 12si alternator. Since A/C is one of the items on the list, I also picked up the vintage air dual bracket for compressor and GM 10/12si, vintage air part 158209. I test fit it, and the result is a 5/8" face offset, with a 3/4" groove center offset. Picture below. I just ordered a 2 groove replacement pulley which combined with a 1/8" shim should get me even with the crank and water pulley. I've done a few searches, and normally I'd take more time and search for a while, but I have an added complication. I'm going to temporarily (but possibly permanently) lose my forward shipping capability effective 1 November (I'm in Riyadh). I really need to get whatever I order in the mail in the next couple of days or I am going to be stuck trying to find a solution in Batha market.

If anyone has used this bracket and come up against the same issue, Please let me know if you have come up against the same issue, and how you solved it. I think the double pulley and shim will work, but if you know a particular offset pulley for the 12si that works for this or some other solution, I'd love to hear it. I'd rather order two solutions and deal with leftover parts than only have 1 and find out too late that it doesn't work.
pulley offset.JPG
 

Steamer

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Jul 20, 2009
Messages
1,607
Location
Miami, FL
Hi. I don’t have your solution but thought I’d add this as it might spark some ideas.

First, I think the alternator you show is a 10si as the 12si has a closed type of fan. “PICS HERE”

I put a 175-amp 12si (clone) on my 74 F.5. which originally had the alt mounted on the left. I modified a 2F alternator bracket which mounted it on the right side to leave room for a power steering pump.
If you can’t find the parts to line yours up, you may have to take the time to modify what you have. It did take me time as I made the spacers with a jig saw, drill press and hand file.

alt bracket 01.jpg


alt bracket 02.jpg


alt bracket 03.jpg


alt bracket 04.jpg
 
Joined
Sep 4, 2021
Messages
22
Location
riyadh
Hi. I don’t have your solution but thought I’d add this as it might spark some ideas.

First, I think the alternator you show is a 10si as the 12si has a closed type of fan. “PICS HERE”

I put a 175-amp 12si (clone) on my 74 F.5. which originally had the alt mounted on the left. I modified a 2F alternator bracket which mounted it on the right side to leave room for a power steering pump.
If you can’t find the parts to line yours up, you may have to take the time to modify what you have. It did take me time as I made the spacers with a jig saw, drill press and hand file.

I've seen the fans both ways, and a variety of pulleys, but mine has the larger 12si back openings. Either way, they pretty much fit the same places.

your brackets are impressive. I'm trying my best to make this work so I don't have to solve this problem again once I'm ready to do the A/C. Also don't want to flush the money I paid for the bracket. I'm hoping someone on here has used this bracket and posts a picture of how their pulleys lined up in the end.
 

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