OK, my tag line says the 911 is out of action and that must change. I have torn apart and rebuit the whole engine but the 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.

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)
Click to view attachment

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

Help?!

Sucks, you have the wrong fan housing.
Easiest remedy may be to buy the correct alternator for the housing.

IIRC shallow is the older less amp alt.

Could be wrong though, it's been a while.

I weld these rings all the time I have 10 of them currently from supertec on the bench and a few from rarlyl8 motorsports and a couple clients. Odds are I can fix what you have and considering we are not that far away from you it would be fairly inexpensive..

I've heard of the failure but never seen it, where do they crack ?

They crack at the vanes - either at the internal or external ring.

Yeah. Sounds like you could. I am leaving town for a week and then I will get back to you. We should have met up long ago.

Still would like to know for sure which alternator goes with the deep recess and more to the current dilemma which goes with the shallow. I tend to believe Mark, but he didn't sound certain.

Posted this on Reenlist and got nothing. Here in the world I got instant help!!

I got an excellent answer at the Pelican site with table

http://forums.pelicanparts.com/911-engine-...tor-flange.html
Click to view attachment
Originally from Tom Butler via Walt Fricke

They also crack all around the alt bolt mounting holes.
The fans themself oval out the holes where the steel pulley rivets to the fan, be sure to check that as well.
Looks like I was right, just didn't want you buying anything without double checking.

An original /6 would have the 1969-74 shallow housing with coil mount studs and a 55amp alt. 1968 and earlier have no coil mount bolts.

'75 till mid 80's had the deep housing and the 70 amp alt. On some of these there is a half moon cutout on the edge, near the timing mark, for the bigger pulley.
Some of these alt's suffered from the big nut treads being damaged.

I have a full assembly (ring, alt fan and pulley) of each, I'm going with the 70 amp external regulator alt.

Yeah, I have the moon cutout on the original along with the other cracks you mentioned. Prefer the external regulator for obvious reasons. More wires but easier to diagnose and fix.

Also some of the 911 guys believe the external regulator is more robust, as the internal reg tends to get cooked over time.

I am actually knee deep into looking at recasting these in magnesium as replacement s..


Worn you got your answer there and if need be I can have a spacer made for you.. Just let me know.

The first ones from vertex where ,sketchy, the last one I had 1 year ago was nice, just a thought...
https://www.vertexauto.com/porsche-alternat...um-p-10218.aspx

FYI the early mag ones can be machined deeper ..

This is what I did new year's eve. My son wanted a new manifold for a Lotus 907 engine he is megasquirting using 4 motorcycle injector bodies. Round at the injector to oval ports. That took making cores.

Click to view attachment

This and the other pour both worked. Making the molds to sand cast the later die cast alternator housings would be a bit harder. Doug decided to make individual runners and weld the castings together to the flange he just cast. There are 914 pistons in the mix and a bit of Audi...

Click to view attachment

Already figuring the clamping to the chuck. Already painted safety yellow.

Click to view attachment Click to view attachment

I am working with a local foundry to try and reproduce the fan rings.. Might do a bunch of them as there is a big demand for them unlike 10 years ago..

Attached are pictures of one's that can't be fixed or can't be fixed cost effectively..

The major issue is that some will rot from the inside and once they do that there is a 50 /50 chance they will weld as they are so contaminated.

Make sure you make the Carrara first. That's the one that breaks the most often and is in the highest demand. I paid $500 from vertex but from what I hear they are getting $900 now. There's is aluminum. Their first gen didn't fit well but later versions fit fine. I have one on my 3.2.

Hi Rory,

I've had two fan housings crack in the past.
One was an early other late version. Both are mag housings.

The pics show where they tend to fail/crack.

I also added the two different alt that I have on hand.
One is internal other external reg. There's a 2 mm difference in between housing width.

after welding, they are going to need machining...making an aluminum one look pretty good , never fail..


thread from 10yrsago
http://www.914world.com/bbs2/index.php?sho...mp;#entry669398

To answer your question about thick housing , what alternator, internal regulated,

tech bulletin above

A while back someone said they bought one off ebay new ?? I dont know the result..there is a thread some where here

418 dollars,, where else EBay

http://www.ebay.com/itm/Porsche-911-Blower...%3D121494388680

double post