Alternator replacement. Any tips or stuff to look out for?
 

There's a whirring sound coming from my fan and I can feel play in it, which makes me think my Alternator is shot (local shop confirmed it). I've never gone diving into the engine compartment of my 911 SC, so I figure this is a good opportunity to learn my way around. Besides, it's getting cold and it's about to be parked till Spring.

I'm a decent set of hands and I don't think this appears to be anything terribly complicated, after reading about it. But, again, I've never had anything apart.

Thanks for any advice.

So there are 2 bearings in the alternator itself and 1 sitting just inside the fan hub. Chances are all 3 warrant replacement while you have it apart. There are only 3 wires out of the back of the alternator, and I do not think you can wire it back incorrectly due to different wire gauges, but just make note of how it comes apart. It sounds like you are going to buy a reman alternator, or are planning to have yours rebuilt. You can also rebuild it at home, but that may be more than you want to bite off.

Also, pay close attention to the direction and order of the pulley parts and shims as you remove the belts.

Check your fan for cracks, and give it a thorough cleaning.

To remove the alternator itself use the drop technique over 2X4's don't hammer on the bolts to remove alternator. There are a few posts on how to do this. Also I would take a picture of what connectors are where. When going to put it back together I got confused. After all its only three wires!!. Take the picture and make a diagram

get a longer ground wire before you start. I believe it's a 84-88 Carrera part number as the OE unit is way too short to work with. this will be the ground that goes from a prong on the back of the alternator to the fan housing. the newer model is a braided copper material that is 6-8" long, where the OE unit is about 3" on an SC and makes it hard to maneuver the alternator around when reinstalling. I ended up making my own with some decently sized wire and crimp type wire fittings after refusing to pay $20 for a fancy Porsche part number unit.... .

With age it's a good idea to replace the ground wire in any case. I believe the ground wire is mounted at one end to the engine case, though(..?)

Don't forget to disconnect the battery before you start work!!

This is great info, guys. Who have you used for the rebuild?

I'll search for the 2x4 method and the longer ground strap. Thanks!

+1 on what both Justin and rekstein1 said, especially on knowing what the connections go where for reconnecting the alternator. I just did this a couple of months ago.
Make sure you can get a new/reman alternator, I had a hard time finding an alternator at the FLAPS, they were all on back-order. Finally got a Bosch reman from a local auto electrical supplier/rebuilder.
Another thing I did was get a longer ground strap - 10 inch I think. Made it a lot easier to get re-assembled in the fan housing, in the car. I could actually pull/lean the alternator out far enough to get my hands down and around the air deflector to attach the nuts that hold the deflector to the back of the fan/alternator.

Craig

My recently acquired 82 SC came with a very recent Bosch reman unit, less than 1,000 miles and it just died. Looks brand new. It's a Paris-Rhone unit "remanufactured" by Bosch but, as has been well-documeted on these pages, the quality of the rebuild process is bewilderingly poor. I took mine today to a trusted local rebuilder and am interested to learn what failed. I will have him use OEM parts if he can find them. I had a similar experience with a Bosch reman for my 01 Volvo, it lasted less than a year. It begs the question, Why offer something of such creptitude? One wishes Bosch would not lend their name to a product and process so awful. John in CT.

Wow, I hope mine lasts longer than that! Or, maybe fail real soon so it is still under warranty :(
I agree, why go through the effort to build/rebuild a product if you aren't going to do it right. Applies to a lot of different areas in this day in age.
Craig

A couple of tech articles with pictures to help you:
Here and here:

You can replace the bearings yourself. Identical bearings to the original (Nakamichi?) are available on ebay from reputable dealers for $30...

I just did my 930, and there were only 2 bearings. 1 big one at the front of the alternator, and a small one at the end. I see folks mention 3 bearings... my car didn't have a 3rd?

Autozone sells cheap knockoff bearings for $10 that fit. I also suspect that any rebuilder you use locally will use these same cheap bearings. Keep in mind a Chevy spend most of its time at 1500rpm, and will NEVER see 6000rpm...

Get good bearings...

Of note, changing the bearings wasn't easy. Took a bearing puller, and a hydraulic press. So, if you don't have these...

The 3rd bearing is the actual fan hub bearing. It is the the most expensive one, and is press fit into the backside of the fan itself. It really is the one that carries all the axial load, and once it fails it then places all the load on the internal alternator bearings.

Buy a $10 voltmeter that plugs into the cigarette lighter. Makes monitoring voltage before and after replacement a breeze.

Make sure your rubber boots that cover the connections are in good order. My first replacement I skimped on this and ended up with a short and second replacement.

Don't be fooled by a lock washer that is on the shaft of the reman units. You don't need it (at least me 3.2 didn't)

that's right! it goes from the air deflector to fan shroud to a case thru bolt. still needs to be longer though.

Ok, I just went from freaked out to confused...

My car only has bearings in the alternator. The fan is hard mounted on the alternator shaft with a key. There is no 3rd bearing.

Looked up the porsche schematics, and they don't show a 3rd bearing either...

dC AutomotiveOver 140,000 square feet of new and used Porsche parts

Pelicans how to articles also don't show a third bearing...

Is this something on earlier cars? There is no bearing pressed into my fan...

Confused?

Bo

Third bearing = muffler bearing.

On my 3.2 carrera, there is no bearing on the fan. And I changed it a few years ago, so if I did it wrong, it's been wrong for at least 3 years.

Just sayin'

As some have said, there's no third bearing in the 911SC alt/fan system. The 964/993
has a bearing in the fan the result of the alt and the fan turning at different speeds.

Thanks for the correction!

Jezza asks: You have a wealth of information from the Pelicans on how to do it yourself, but I'll try to answer your question.

Since you live in a large metro area you should be able to locate a local auto-electric shop that can handle it. In my city the expert guy couldn't find the parts. so I sent mine to Sagle Auto Electric in Zanesville, OH. I can't remember how I found them but probably through someone on this board. Google them and be sure to call them first - great bunch of guys. They replaced the brushes, bearings, diodes and rectifier. (My alternator has an external voltage regulator, not sure about yours.) Total cost was ~$150 which I thought was worth it. You'll pay shipping to them and I think the cost included shipping back. These guys will stand behind their work 100% and Porsches are their specialty.

I read on this forum that you should rebuild your own rather than buy a rebuilt or new alternator for quality control reasons. The older base units were just better.

Removing the fan and alternator is a total pain, at least on my '73. Just be careful not to bang up the fan in the process. If it's pitted and so forth, you might consider having it refinished. The best in the Porsche world is Mark Motshegan in California. Do a search on this forum or google him for his contact info, as I've lost mine. He refinished and "repainted" mine through a special process that does not involve powder coating. A bit spendy but if you have a cracked and pitted fan, your engine compartment will look much better.

Best,

Tom

Tom, thank you for saving me the trouble of searching. Definitely want to get the original rebuilt. I am very interested in approaching this myself, but have literally, only changed the oil in my 911 since buying it 2 years ago. Everything has been replaced <6k miles by the previous owner (except the alternator, apparently). Anyway, the $850 the local Euro guy quoted me is not the issue, as much as me not wanting to feel like a d1ck and pay someone to do my work, as I have a heated garage and all of the tools. Thanks again, I'll contact them on Monday and read more about the job.