alternator support - depth of alternator flange

[worn]

Almost done with my rebuild but the alternator housing /fan shroud is cracked, seeing as how it is magnesium. I bought a nice used one and it has the same casting number as the old one. But it is different. Both say 930 106 006 5R, but they are from different casting dies.

In both the support vanes go to a mounting flange for the alternator. The hole the alternator goes into is the same diameter. The difference is the hole that the alternator fits into is deeper in my cracked original and shallower in the new one. PET says there was a change at the 80 year and I have an '80 SC. With the shallower hole the alternator goes in less and the studs for fastening just barely fit through. No room for a nut. Also, I think the fan would be rather out in the shroud.

What I am trying to find out is how to get an alternator to fit the thick flange newly purchased shroud. One question is which is newer and which is older. Here is a photo of what Vertex sells (but doesn't make). It looks pretty much like mine.

Net is slow for me - couldn't get it to load..

You can get spacer rings for alternators that normally go with a shroud with a hole that is shallower.

[Flat6pac]

Basically, off the top of my head, what you need to look at is the combination of housing and alternator.
From 75 on the back flange that the alternator sits on is approx. 19mm. That number is good through 83. Using either an alternator with external voltage regulator (fine thread,22mm nut)or a Verlo alternator with onboard VR, (24mm nut, 8mm Allen)
Now, in 84-89 Carreras used a larger alternator so the backing thickness became thinner on the housing, about 6mm. Alternator is Verlo or Paris-Rhone still with 24 mm nut and 8 mm Allen.
The Carreras alternator will not fit the housing as you describe.
From your description, you have the correct housing (unless it's 78/79, using a smaller fan)
And a Carreras alternator. Spacer rings can be purchased but that doesn't seem to be your problem.
Bruce

[Walt Fricke]

If you can't trade for one which has the spacing you need, you can have yours machined. Getting the alternator where it is supposed to be is critical, because the crank pulley and the fan pulley centers have to be dead on. If there is any offset you will be continually throwing fan belts.

[Walt Fricke]

Here is the chart Tom Butler posted a while ago for all of this.

[worn]

Thanks Walt,
Looks like I plunked for a 69-74 to fit my 1980. There goes several hundred bucks. Fortunately - I have a lathe...and I am not afraid to use it.

You guys are great. Wanted to make exhaust smoke by Christmas, but decided that was a poor use of my priorities. Now I can mount the motor.

[Flat6pac]

A 930 casting number isn't 69 on.
From 69 casting number would be 901
Before you cut make sure you know which alternator you possess
Bruce