Thanks to you both! :veryhappy
Doug
Doug
GM SI alternator mount using original lower bracket
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
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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.
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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.
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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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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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Final mounting of 94 amp 12SI alternator
Here are some pictures of my final mounting. I ended up making two version of the upper adapter to work with the stock upper arm. I didn't like the black one as it came out too short to provide a full swing of adjustment for belt tension. Once the lower was spaced and set to align with the crank and water pump pulley I noticed that a 3/16" or so thick flat bar would work perfectly with some tweaking as the extension.
So I made my second upper adapter and shaped it to insure alternator fan clearance as well as full adjustment swing. Once everything was tightened down it is VERY solid! And should be able to use a stock belt. I will double check that later.
Anyway, here goes with some pictures.
Here are some pictures of my final mounting. I ended up making two version of the upper adapter to work with the stock upper arm. I didn't like the black one as it came out too short to provide a full swing of adjustment for belt tension. Once the lower was spaced and set to align with the crank and water pump pulley I noticed that a 3/16" or so thick flat bar would work perfectly with some tweaking as the extension.
So I made my second upper adapter and shaped it to insure alternator fan clearance as well as full adjustment swing. Once everything was tightened down it is VERY solid! And should be able to use a stock belt. I will double check that later.
Anyway, here goes with some pictures.
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You better put a large star type lock washer between the brackets because no matter how solid it feels while sitting on your bench it will begin to fold up and loosen the belt when you have vibration from the motor. I have one of those alternators in a box brand new that I never used because I didn't like the way the bracket worked and I went to the trouble to combine an aftermarket bracket with the stock one (welded together) and then had it chromed. It is in the attached picture on the right before I sent it out for chroming. The alternator that I wound up with is 105 amp chrome one and works with the stock bracket.
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True, I am and was concerned about buckling/slipping when I set it up. A dowel pin can prevent it hinging easy enough. Or do what my first intent was and make a stouter upper like my first one in the picture, just with the correct center to center spacing on the mounting holes. That may still happen, probably will actually now that I found my flat bar I was looking for in the first place! 
at:
at:
Opel bracket didn't work
Today I tried adapting the stock aluminum bracket to work with the GM 105 amp alternator that I had. It is from Autozone - a Duralast 1532-6-7 with the 10 o'clock mounting that I've used previously in my GT and Manta with the F bracket. Upon completing the shim swap and some grinding I discovered that the cooling fan on the alternator will not clear the bracket.
The alternator used by the OP is different and does not have the clearance issues that I had. Looks like it's back to the F bracket for me.:sad:
Today I tried adapting the stock aluminum bracket to work with the GM 105 amp alternator that I had. It is from Autozone - a Duralast 1532-6-7 with the 10 o'clock mounting that I've used previously in my GT and Manta with the F bracket. Upon completing the shim swap and some grinding I discovered that the cooling fan on the alternator will not clear the bracket.
The alternator used by the OP is different and does not have the clearance issues that I had. Looks like it's back to the F bracket for me.:sad:
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