1979 911SC alternator too short
 

I just replaced the alternator in my 79 911SC with a rebuilt unit...(externally regulated) and the fan seems to be too far recessed into the housing about 1/4 inch. After remounting the fan onto the alternator shaft, the fan pully seems to be about 1/4 inch inboard if you run a straightedge up vertically from the crank pully.
The belt rubs on the bottom of the housing where it is closest to the crank pully becuase it is running at such and extreme angle from vertical.
Anyone experience this problem when replacing alternators?

From what I can tell the alternator can only be seated one way in the housing ....it bottoms out against the housing when the mounitng bolts are torqued down.
The dealer who sold me the rebuilt unit (Valeo) swears there is only one size alternator for that car and that it cannot be too short.
What is wrong here? I don't want to have to remove the alternator and return it to the supplier again as it is such a job to get it in the first place.

The dealer is wrong, wrong, wrong.

There are a few different alternators and shrouds to match.

For example, I had a carrera alternator, and it wouldn't fit in the 901 housing. Then I got a 4R housing, and the bolts were too short. Then finally I got a later revision and everything worked.

they probably gave you a 55A unit, which fits earlier 70s cars. the proper 75A units are taller.

Dealers are not just more expensive, they're also more ignorant and slower, too. With just a few notable exceptions, right Laura?

Fred,
Did you replace the thrust washer? You know if you forgot, the fan will go ding a ling a ling against the housing.
Trust me, I know.

Ned Monaghan

John Walker is correct! You got the wrong alt. You need the (bad -
worst of any alt. if internal reg. Valeo) 75 amp to replace your 70 amp
Marchel with an external reg. They gave you a 55 amp.

You need to check what you're getting from the flakes supplying parts.
The complete alt. housings have different lengths.

Have Fun
Loren
'88 3.2

huh? Valeo=Worst?

As I said on the other post, "The Paris-Rhone/Valeo internal regulator
alternator is the worst alternator manufacturer Porsche ever used."
The 55 and 75 amp replacements are mostly from this manufacturer.
Their are also some other junk units which are mods of the stock
911SC Marchal alternator.

Just get the original 70 amp rebuilt properly and avoid the junk alternators.

Have fun when the alt. starts to overcharge and damages your
electrical system!

Loren
'88 3.2

So it’s the internal VR you have had problems with. I bought an “OEM” VR to replace one on my P-R alt., but the P-R VR only had one wire! In the end, I just bought a Valeo.

Funny thing is that the "OEM" VR part looked like it was made in Italy. The name escapes me now, but Italian electronics has a reputation as good as Lucus does.

Regardless, if it’s a VR issue, I’ll just replace it. It just seems odd that you would make such a strong statement when others have not complained about the Valeo longevity. ..at least not so loudly or frequently.

My thinking on this has switched 180 degrees- I used to think that the internal VR was a good thing, until the warning light kept coming on during practice for the Gingerman club race. 100F temperatures, coupled with heat-soak of the VR because it's located about 2" from the engine case, were causing it to SHUT DOWN, turning on the warning light. Naturally, within 1/2 second of the light coming on I had shut off the motor and pulled into the grass, to the consternation of the corner workers, but I wasn't about to cook the engine because of a broken fan belt!

Over the winter I'm switching back to an external VR, mounted inside the car on the hat shelf. I'm going to put two of them there, with a cannon plug, so if one fails I can switch to the other one. Also the early 55A alt is lighter weight than the later 90-amp Carrera type that I so brilliantly installed! And it gets rid of the 930.xxx casting number on my fan, which always raised scrutineers' eyebrows!

Good thoughts John, but why did the Factory start recommending the onboard VR? I'm not saying the Factory did EVERYTHING right, but I'm curious. Heck, the only thing that's done right on my car is the second time I had to fix it...after I tried the first time and found it didn't work per my re-engineering :D ...then it's what worked for the Factory or someone with tons more mileage than I do.

Souk,

Improvements in semiconductor technology made internally reg'd alternators possible in the late '70s. It's cheaper, and less complicated, to have an internal VR than to have a separate DF wire and require an external plug and metal-can style voltage regulator. And it's also a truism that fewer connections in a circuit can reduce the likelihood of failure- they tend to fail at connectors due to fatigue and oxidation, not in the middle of a wire. So I can see how they wanted to make the update in '82 for the street cars.

But HEAT is the enemy of electrical circuits and that's where they went wrong, at least for a race car. I got a new book on the history of Porsche and there's a great shot of three VR's mounted on a board in the cockpit of the 956!

I agree with you that the factory wasn't always right- five blade fans, thermal reactors, trombone coolers, cold-start systems, etc!

John is right! The key is the heat problem; to the semiconductors
and to the thernal expansion in the VR package with the potting
compound used.

It's a problem for alternators that are mounted outside on water
cooled engines (the alternator gets hot too) but to a lesser degree.

Have Fun
Loren
www.systemsc.com
'88 3.2

FWIW...I replaced the OEM voltage regulator on my 85 Carrera ( internal type) with an aftermarket, German-made HUCO, and all is better. Much larger heat sink fins, for one thing...and yes, heat is the enemy.
--Wil Ferch

Only time will tell, Wil. If I had the motivation and time, I'd
take the internal reg. out of my alt. and use an external one.

Have fun
Loren
'88 3.2