GM SI alternator mount using original lower bracket

11752 Views 58 Replies 22 Participants Last post by Red0ktober, Oct 21, 2017

First opel 1981

Discussion Starter · Mar 31, 2014 (Edited)

12

I was playing around with the GM SI alternator and figured an easy, painless, way to use the original bracket.

I am sure a few would like to know how I did it so here's the write up.

First thing I did was look to see how different the lower mounts were. There's enough of a difference so that you can't just put the alternator into the factory bracket but as you see from the following pictures, not so much that it's not doable.

I first measured the position of the pulley vs the lower mount on the alternator.
I discovered that the back part lines up within a few thousands of an inch but the front was shorter on the GM alternator by approximately 0.2 inches

I figured if I have the right shim in place then I could just space the front and everything would be cool, right?

So now I fitted the bracket to the alternator to see if the mount clears the housing.
With the factory bolt it would but there was never going to be a situation where it would fit centered in the hole. This could cause problems down the line.

So, still using the factory bolt, I utilized the fact that the mount had been sprayed black and moved it a few times to see how much, and where, it was binding.

I then observed that there would be plenty of meat left on the bone if I ground it down to clear with a centered bolt. I ended up grinding off about .050" of the mount to clear. The alternator housing has a slight angle to it so one side needs to be ground more than the other.

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Opel GTs are not GM products
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Humans are not an endangered species!
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1 - 20 of 59 Posts

poor gt (R.I.P)

· #2 · Mar 31, 2014 (Edited by Moderator)

I guessing this is the steel lower bracket, Opel also made an Alum. lower bracket that takes a shorter alt. belt. That would be too much stress on the Alum. :ugh: I have an extra NOS steel bracket if someone needs one for this mod.

First opel 1981

Discussion Starter · #3 · Mar 31, 2014

12

Next, I made a list of the hardware I would need and headed off to Ace Hardware.

I purchased it all in stainless steel because it's not that much different in cost to zinc coated to make it worth my while to have rusty bolts in a year.

This is what I got, for about $10

First thing I had to do was to remove the old shims for the rubber grommets because we will be using a 3/8 bolt to fit the GM SI alternator and the shims are smaller than that. They are glued in but it's not too hard to figure a way to remove them using a 1/2 socket, a allen head socket, and a C-clamp.

Then it's really easy to push the new shim in

I thought it would be really important to have the washers in the proper order to make sure everything stays in place.

And this is the final assembly.

The order of assembly is:
Bolt
Flat washer
Bonded washer
Rubber grommet (with new shim inside OE mount)
TWO thick washers
Alternator
Rubber grommet (with new shim inside OE mount)
Bonded washer
Flat washer
Nylock nut.

The parts list is:

3/8-16 X 5" bolt
(2) 3/8 flat washers
(2) 3/8 .010 thick washers
(2) bonded washers
(2) 3/8"ID x 1/2"OD x 1" shim
3/8-16 Nylock nut

I used a nylock nut because I don't want to over tighten the mounting.

Everything is stainless.

I have not tested this on the engine yet but everything seems to be lined up.

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Opel GTs are not GM products
̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—
Humans are not an endangered species!
̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—

Reactions: 5

First opel 1981

Discussion Starter · #4 · Mar 31, 2014

poor gt said:
I guessing this is the steal lower bracket, Opel also made an Alum. lower bracket that takes a shorter alt. belt. That would be too much stress on the Alum. :ugh: I have an extra NOS steal bracket if someone needs one for this mod.

Actually this was using the aluminum mount.
The length of the belt shouldn't make a difference.

There's really not much of a difference in the dimensions, once mounted in the factory bracket, to change the stress load on the lower mount. The length of the belt shouldn't change that in any significant way.

Opel GTs are not GM products
̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—
Humans are not an endangered species!
̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—

poor gt (R.I.P)

· #5 · Mar 31, 2014 (Edited by Moderator)

I wouldn't think the length of the belt would change the stress load, those will be felt when the engine is revved. Just thinking that the steel takes a longer belt, it might stand farther off the alt. or block, don't know for sure, might not need to mod. it, but the offer still stands, for the steel one if you want it, that alum. is not that thick to begin with, broke one a few yrs. ago, just my 2ctw :lmao:

First opel 1981

Discussion Starter · #6 · Mar 31, 2014

poor gt said:
I wouldn't think the length of the belt would change the stress load, those will be felt when the engine is reved. Just thinking that the steel takes a longer belt, it might stand farther off the alt. or block, don't know for sure, but the offer still stands, for the steel one if you want it, that alum. is not that thick to begin with, broke one a few yrs. ago, just my 2ctw :lmao:

Well, if you want to pass it on to someone who will use it, I would certainly like to use it.
I will PM you.

Opel GTs are not GM products
̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—
Humans are not an endangered species!
̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—̶̶̶̶̶̶̶—

OrangPeEL

· #7 · Mar 31, 2014

Nice write-up!

Nice write-up! I got about that far on aluminum OE lower bracket mod about 10 years ago, but gave up and went w/the steel GM F. Kinda recall upper bracket mounting boss (when SI alt pivoted in/up against distributor) was farther out & around than I thought I could fab a good upper bracket for. Epic fail for me! :ugh:

Reactions: 1

Aardvaark (R.I.P.)

· #8 · Mar 31, 2014

Been sitting on a new 105 amp GM alternator for years planning to replace the 45amp original on my 75 Manta. Your post may get me off the dime and get er done.

Gary

· #9 · Mar 31, 2014

Aardvaark said:
Been sitting on a new 105 amp GM alternator for years planning to replace the 45amp original on my 75 Manta. Your post may get me off the dime and get er done.

If you do, make sure that you replace your ammeter with a voltmeter.

I left my lights on one night and came out to a dead battery. Jump started it and drove off. A couple of minutes later smoke came out from under the dash. The Opel ammeter didn't like being overloaded by a 100 amp alternator.

Aardvaark (R.I.P.)

· #10 · Mar 31, 2014

Gary said:
If you do, make sure that you replace your ammeter with a voltmeter.

I left my lights on one night and came out to a dead battery. Jump started it and drove off. A couple of minutes later smoke came out from under the dash. The Opel ammeter didn't like being overloaded by a 100 amp alternator.

Thanks for the reminder. I will re-read all the past posts on alternator upgrading before attempting it.

Lindsay

· #11 · Mar 31, 2014

The best SI alternator bracket modification that I have seen, especially to keep the Opel lower bracket with the isolation bushings.

http://www.opelgt.com/forums/1a-2-a...sing-stock-upper-bracket-belt.html#post482306
Although I do not have a MIG Welder, I like this modification for the SI upper bracket.

Does this qualify for a Sticky so it doesn't get lost?

kwilford

· #12 · Mar 31, 2014

Lindsay said:
Does this qualify for a Sticky so it doesn't get lost?

Sure....

Reactions: 1

opelgtraj

· #13 · Aug 8, 2014

Is it possible to get the alternator Part number for this modification?

Seems to be multiple starter generators with various part numbers that can be used.
Thanks.

Aardvaark (R.I.P.)

· #14 · Aug 26, 2015

Gary said:
If you do, make sure that you replace your ammeter with a voltmeter.

I left my lights on one night and came out to a dead battery. Jump started it and drove off. A couple of minutes later smoke came out from under the dash. The Opel ammeter didn't like being overloaded by a 100 amp alternator.

Well typically of some of my projects I'm just now getting around to doing this on two cars and realized the SI-10 105Amp I have is a one wire self exciter that I bought from Kent Darsey some time ago after he somehow ended up with two. (Wonder what he is doing these days. Haven't seen him around town either.)

Anyway I decided in the meantime to use this one wire SI-10 on my 1963 Thunderbird to upgrade it's original type 45 amp Ford alt.
So I bought a new CS130 105 amp one-wire self excited for the Manta which hopefully will get installed after RT66. Will just have to remember to goose the throttle on starting.
My manta doesn't have an ammeter (or voltmeter) so the overloaded ammeter isn't an issue.
Why is it that now that I'm retired projects take even longer to start and finish.

rcvowell

· #15 · Nov 9, 2015

Slight option to this method

I made a small discovery when following this idea for modifying the 94amp 12si that I picked up for my lil GT that lends itself to a bit of an option to this method.

I started with fresh lower bushings, and after a bit more fight to push the inserts out than I cared for, I started scrounging for materials to sleeve the alternator itself to retain the original bolt and still center the alternator on the mount.

What I found in my stash of leftovers was a piece of poly irrigation line that had a wall thickness that was just about but the diameter was way to big. A good pair of scissors had no problem splitting it cleanly and straight, then slowly trimming it down lengthwise to get the diameter correct and have a tight seam when inserted into the alternator mount. The OE bolt is a snug fit and does not wobble at all.

The same gentle grinding and sanding still apply to the lower bracket, mine required a bit on the front for fan clearance and rear lobe for housing clearance. I used the aluminum bracket as it is lighter and this project requires all the weight savings that I can obtain.

Now I just need to setup the shims to locate it properly for pulley alignment and it's good to go.

I can take more pictures later if anyone wants more detailed information. I haven't setup my upper yet, but will putter with that this week.

I really liked First Opel's idea as it was a clean and simple approach to the mounting issue and I would have cloned it if not for the sleeves in the new bushings fighting me.

I hope this opens up another, possibly easier option for those wanting to run a 12SI alternator in place of the OE unit.

As a side note, the AC Delco number for mine, 94 amp, clocked at 3:00 (regulator terminals as viewed from rear) is 3342193 or 10497079, both numbers work. Mine came from Rock Auto for $70 or so.

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rcvowell

· #16 · Nov 9, 2015

opelgtraj said:
Is it possible to get the alternator Part number for this modification?

Seems to be multiple starter generators with various part numbers that can be used.
Thanks.

Here is the one I just used. I am not complete with it yet, but my lower is about done with a slight modification to the process.

3342193 or 10497079, both numbers work. Mine came from Rock Auto for $70 or so.

Aardvaark (R.I.P.)

· #17 · Nov 9, 2015

Don't want to turn this into a parts for sale thread but I decided not to use the new si10 105amp on my Thunderbird. It's plugged and wired and standard US shipping is free for $60. See Ad board.
End of my shameless plug.

slracer

· #18 · Nov 9, 2015

My GT has a replacement alternator, but it is still low amperage so I will be doing this before it hits the road. I noticed that rcvowell has a 12si xxxx for the alternator number and Aardvark has a 10si yyyy for his number. Can anyone tell all of us what those numbers mean?

Thanks, Doug

Lindsay

· #19 · Nov 9, 2015

slracer said:
My GT has a replacement alternator, but it is still low amperage so I will be doing this before it hits the road. I noticed that rcvowell has a 12si xxxx for the alternator number and Aardvark has a 10si yyyy for his number. Can anyone tell all of us what those numbers mean?

Thanks, Doug

12Si series alternator has several design improvements over the 10Si series that make it the better choice between the two.

Catalog
DELCO REMY models 10SI & 12SI alternators

https://alternatorparts.com/10si-12si-high-output-alternators.html
10Si and 12Si Series High Output Alternators

rcvowell

· #20 · Nov 9, 2015

slracer said:
My GT has a replacement alternator, but it is still low amperage so I will be doing this before it hits the road. I noticed that rcvowell has a 12si xxxx for the alternator number and Aardvark has a 10si yyyy for his number. Can anyone tell all of us what those numbers mean?

Thanks, Doug

Here is the link that I found that compared them when I was studying them.

12SI and 10SI comparison

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