Your posting of the alternator rebuild is great!

The question of cost is interesting - here is the Pelican cost number ---

964-603-156-AX-M14

Bosch 115 Amp Rebuilt Alternator, 911 Carrera 2/4 (1990-98), 911 Turbo (1991-97), Each
Brand: Bosch Original Equipment Manufacturer at the time of the vehicle's assembly [More Info]

$258.00

I have copied your write up and pics into my library file.

Thanks for your time and effort put into this thread,
Regards,
Roy

Nice, and thanks for that parts link.

I tend to rebuild things given most commercial rebuilds aren't all that great. Also, good to see proper bearing installation technique used. ;)

Great write-up, JWPATE, very thorough.

Small world....NSK in the UK were one of my customers last year - I spent many-an-hour on the train up to their plant up in Newark visiting them, know their IT guys very well. Funnily enough, I did wonder whether me knowing them could pay dividends when it came to sourcing bearings for the car projects - looks like it could do!!

Cheers
Spencer.

Great Thread
 

Thanks for taking the time and attention to detail. Very very nice.SmileWavy

Looking at the slip rings, especially the one closest to the bearing, it is extremely worn.

If you have a look within the gap between the slip rings and the bearing, one can sort of see the original thickness of the slip rings, and they aren't that thick to start with. I would guess 3 mm at most.

In another pic, I see that you turned them down on a lathe, which is what a lot of re-builders do including Bosch.

That brings me to the topic of "rebuilds".

From the Bosch site...
Well hell, I can do that at home. One really needs to ask what "remanufactured" really means. Well at least they install new bearings.

A rebuild should include new bearings, a new diode plate, a new voltage regulator and a new slip ring assembly, all to OEM specs.

"A rebuild should include new bearings, a new diode plate, a new voltage regulator and a new slip ring assembly, all to OEM specs." [/QUOTE]

In checking around, there is NO alternator rebuilding firm in the business, that I know of, which will rebuild to your suggested standard. As you said, what you get after ordering a rebuilt alternator, will be a cleaned up unit with turned slip ring, new brushes, and Chinese bearings.

I have it from other members who have opened up the BOSCH RE-MANUFACTURED units and found the bearings to be Chinese in actual fact.

As to this particular set of slip rings, I did consider pulling them off and changing, but the wear did not warrant it in my view. After turning, the rings were 27 mm as apposed to 28 on new rings (which also must be turned true). That one MM of wear took 22 years to accomplish, and 72,000 miles.

I will not still be around after another 22 years. So I decided new rings were not appropriate.

Which is why I'll rebuild it myself when the time comes.

If these things are so "thoroughly tested" as they so love to advertize, then a local owner would not have to had installed a new voltage regulator on a rebuilt alternator he just installed. My time to remove and install is worth more than the alternator to me.

Actually a radius of 0.5 mm wore.

You didn't happen to measure the ID of the slip ring or the thickness of it by trying to measure along its side? Its the thickness that matters or what is left after turning.

Again, great write-up. I've gone to your links and bookmarked them.

That's exactly right Alex. The radial wear on the deepest of the two groves was right at .5 mm.

I did have a look at the ring thickness, and it seems to be about 3 mm. Not easy to measure on the installed rings, but I had access to a new ring.

I am currently rebuilding my 95 993 alternater with 76000 miles after the rear bearing went dry and started to squeal. No damage caused ,caught it in time. I am only able to get my hands on SKF replacement bearings locally which are packed with a lithium grease and a temperature range of -30 to +120 c. Does anyone have any temperature specs for the OE bearing. I can't find it anywhere. thanks

Fantastic write up !!! Thank you
Did you ever press out the old hub bearing and see if a replacement could be found?

Thanks!

I never did...yet.

Its a 17 mm ID x 32 mm OD x 14 mm wide, double row ball bearing.

I did find some 17 mm ID x 32 mm OD x 7 mm wide bearings, so if two of them were stacked, that might work.

Pics of the fan hub and bearing.

No, I never did find a replacement bearing which I would be comfortable using.

Traveller, in his above post, has listed the size accurately. And, it is a double roll, ball bearing, similar in design to those used on all four wheels of our cars. It just is not a common size, and I did make several calls, attempting to locate a replacement.

Yes, two single row bearings (easily available and cheap) could be put in there, and the space used would be the same. Here is the problem with that though. Like our wheels, the engine fan also puts considerable axial force on those bearings, and the single row design is designed only to handle only a radial load. Using two single row bearings, although they would fit up OK, would have a short service life.

I wonder since the original dual row bearing is no different in groove design. I'll check with the tribology lab at work this week. Unfortunately, the head tech retired a few months ago.

One thing though about stacking bearings of this type should axial clamping force be applied to the inner races, there should not be a gap between the inner races otherwise side loads are introduced and ball bearings do not take those well.

Thank for the update... looks like I'll just have to order a new hub then.

Out of curiosity, where did you acquire the voltage regulator?
I priced it at Sonnen and it's $158.00

Thanks

I ordered it here. Have your alternator Bosch number ready when you call.

Smith Co Electric - Starters & Alternators, New & Remanufactured

They are about 30 minutes away from me, I'll stop by.

Thanks

Wonderful writeup - thank you.


Andreas

Having just rebuilt an alternator for a local 993 owner, note that the bearing at the pulley end is of a different size.

Alternator label on the unit I just rebuilt - note the Porsche 964 part number which is what is listed by Porsche for a 993:
Bosch 0 120 468 125
N1 – 14V 40/115A
Made in Germany
LWD – 1145
964 603 156 01

The above alternator takes a 17 x 52 x 17 bearing at the pulley end of the alternator. The one removed was labelled: NSK B17-99DW8, England. The WBD part number for this bearing is: 10-3043-4W.

The bearing at the slip-ring end is the same at 12 x 32 x 10. The one removed was labelled: NTN 6201 LU.

Note: due to the location of these alternators, a bearing with a high temperature grease should be chosen.

I will be going with WBD bearings when the time comes. They claim that they use a grease with a 200°C rating. I'd upload their product sheet, but its in PDF format. Here is some on-line info on WBD Bearings.

wow great thread. I think this is over my head. Any suggestions on places that do a good job of rebuilding in the Austin, TX area? I was thinking of buying a rebuilt unit from Pelican but so far I heard mixed reviews. Have the supply gotten better?