Fan, housing, and alternator compatability questions

[weare138]

Hi,

So I'm in the process of rebuilding the Motor for my 1978 911 SC and as it turns out just about every component that can wear out or fail in some way has( If only i had read more on this forum before I bought the car. I have no one to blame but myself for this mess). I've gotten to the point where I have to address the fan and housing. The housing is badly cracked. The fan has hit the housing and has several blades with pieces missing. The alternator looks like it has been set on fire and feels like garbage when you spin it.

As far as I can tell all three parts are junk. I am also aware of the fact that 78/79 fan housings are hard to come by. In chatting with a vendor it was mentioned I could just throw the fan, housing and alternator from a 3.2 carrera in. So, after the excessively wordy lead in, Is this just a bolt in deal or am i going to have to futz around a bit to make this work. Will i have to modify any thing like (wiring harness, fan-shroud, little air guide thingy) to put a fan, housing and alternator for a 3.2 carrera in my 1978 sc.

Thanks you for your input in advance.

[Grady Clay]

weare138,
First, welcome to the forum
You will find a lot of help here.

First, your ’78-’79 226 mm fan and housing should be practically free as many remove the small fan and replace the fan and housing with the larger 245 mm version. Search Pelican and you will find a LOT of info.

Your engine already has the large 134 mm crankshaft pulley. Converting to the 245 mm fan with the small 80/84 fan pulley, you will get the desirable 1.82:1 fan ratio.

As far as the alternator, simply exchange for a rebuilt one from our host.

I agree a complete assembly (fan, housing and alternator) from a Carrera is a good solution. Yes, it is bolt-in. You still may need an alternator rebuild.

All the late (and many replacement) alternators have an integral voltage regulator. Is yours external or internal? No wiring change is necessary for all this, simply leave off the external regulator if the alternator has one internal.

Best,
Grady

[euro911sc]

thats actually sounding like a good idea. If you get a late Carrera set you will also get more amps on the Alt which would be useful. I believe there is an article in Panorama about upgrading your earlier alt to a latr one and it described what wiring changes were necessary if any.

No actual knowledge here, but if you swap the whole set I think you should be good. In the article above, Im pretty sure that if you can upgrade you Alt that the fan housing has the same mounting loacations and mount diameter for the Alt. You may need to modify the little plastic part, air deflector, slightly to fit the desired alt.

The issue comes with the engine shroud fitting the fan housing. Holes between your SC and Carrera's are slightly different, but its just fiber glass so you could cut and paste it till it fit right. I suspect it will all bolt up no problem, though.

Best regards,

Michael

[Ken911]

nope the fan housing is different. the earlier alternators were shorter. if you go with the newer carrera alt then you have to get the newer fan housing. I found this out when my fan housing on my carrera cracked. didn't want to spend the cash for a new aluminum after market one. Bought one on evil bay that was supposed to fit and it didn't. luckily there is a machine shop where i work and I was able to get it turned to fit the thicker alternator. so your best bet would be buy all new matching carrera parts. you will just have to drill and tap the new housing for the studs for your coil.

[Grady Clay]

Ken brings up a good point. As the amperage capacity increased, the alternator dimension axially got longer. To accommodate this, the fan housing surface where the alternator mounts moved away from the pulley. The fan housing casting also changed to accommodate the change in mounting. Only a few fan housings will allow machining to the next longer alternator.

Aside from the alternator depth issue, I think the housings all interchange exactly ’69-‘83. The ’68 mag housing is somewhat unique but can be used back to ’65. The aluminum sand cast housing was from ’65. John Cramer identified an early 250 mm fan and housing.

Am I correct that the only difference with the Carrera fan housing is one mounting to the fan shroud is relocated about 5 mm?

Am I correct that the only difference between the ’84-’89 Carrera fan and the ’75-’83 (except ’78-’79) 11-blade fans are the alternator cooling slots in the hub?

Best,
Grady

[Ken911]

I had to cut about a half of an inch out of it if i remember correctly. it ended up being pretty thin on the back side of the mounting ring but the original one was pretty thin there too hence the cracks. i set it up on a table and measured the distance the fan stuck out from the correct location then took it all back apart and when i pulled the alternator out i noticed the dirt line left by the old housing was roughly the same as my measurements so I re measured from the front of the alternator t other back then measure from the front to the line of dirt then measured the front to back difference in the shroud. and came up with the exact amount to cut out of the shroud. it fit perfectly. and of course the guy in the machine shop was all psyched about it cause he wanted to take all the magnesium shavings home to light up.

[304065]

Funny this comes up, I was just working on my alternator yesterday. It's an internally regulated Carrera type.

The super early 901 version was identified by Alan.UK here, not I, but the later fan and alternator wont' fit. These are best left for SWB restorers.

The early 901 version 0R doesn't fit either. As Grady says, the thicker Carrera alternator sticks out too far.

The second 901 version, which I believe is a 5R 2,7 part, needs to be machiend as Ken says. I started doing this and realized I was weakening the part so I stopped.

The first 930 version is the one you want, it's got bosses threaded to mount the coil on the shroud, I believe it's 5R.

The second 930 version (84-89) has no coil studs, so you will have to relocate your coil, complicating things.

I have a Carrera fan that I'll be installing on mine, will snap some photos.

I don't recommend the conversion to internal regulation. Unlike virtually every other car on the planet where internal regulation is a good idea, in a 911, you don't want the VR two inches from the engine case in a high vibration location. When I do mine over again I'm relocating the voltage regulator to the package shelf.

Heat soak of the VR will cause it to shut down, which will turn on the warning lamp. There is nothing more frustrating than having the low-volt lamp come on, making you think you broke the fan belt and coming into pit in a race that cost you thousands in entry fees and logistics, only to realize that your internal VR has overheated and thrown up its hands.

Look in the cockpit of a 917 or 956 sometime, there's a board to the side of the driver with all the relays and electrics mounted on it. Easy to diagnose and away from heat and vibration.

[Henry Schmidt]

First ,weare138 welcome the the forum
We have a bunch of 225mm, 78-79 fans and would be happy to sell you one of them. You choose, sell me your housing or you can buy a fan. Like all parts we sell the price will be reasonable.

Glady
Do you know where to buy these housings?
It would be my pleasure to buy any "practically free" fan housings that use the 225 fan. We use them on almost all off our race engine, just like Porsche factory did.

[Grady Clay]

Henry,

They are sitting in people’s garages. I saw three at a swap meet a couple of years ago. They didn’t sell at $25 for fan and housing. One even had an alternator of unknown quality.

Try a WTB in the classifieds.

Best,
Grady

[Mysterytrain]

I have a 78 sc and replaced the fan and housing with a larger assembly from an 80 -on SC. My original fan housing had a casting number of 930-106-101-0R the 'new' housing is 930.106.102 0R. The alternator fits perfectly and is spinning a little faster.

[weare138]

How hard is it to find a housing fan etc. for an 80-83 sc? I kindof want to go with whatever is going to cost me the least and still work. This rebuild has totally destroyed my finances . I just think that putting the broken fan back in my cracked housing attached to my sloppy looks like it's been set on fire alternator is asking for trouble down the road. I'm okay with using an older alternator as I believe I have an external voltage regulator sitting on the drivers side of my engine compartment.