Awesome write-up. This should be a Tech page.

Two questions: Do the windings ever fail? What is the life expectancy of the stator and rotor windings?

Are these bearings and brushes available for older cars?


Thanks again for such a great thread.

There really is not reason for the stator windings to fail other than at the solder joints at the diode plate. The stator is stationary.

I have seen failed connections between the rotor winding and the slip rings due to vibration and due to that junction not being tied/taped down properly. The slip rings will wear of course and as a minimum should be dressed if new brushes are installed or a new voltage regulator with brushes is installed. If the slip rings get too thin, then new slip rings can be installed.

A short or open are another cause of failure.

I should have been more specific. I have had a generator fail because the insulation on the stator windings failed causing a short to the case. I get the impression that this is not usually a problem with these alternators because the windings are not generally replaced during a rebuild. Is my thinking correct here?

Also are these bearings and brushes still available for SC alternators?

Well it can always happen as I mentioned above regarding shorts and opens. The windings can be dipped during a rebuild.

Winding are not replaced during a rebuild from major rebuilders either. I would hope that they at least dip them.

Check the thread starter's links.

Great thread, thanks!

Do you know if this is the first time the alternator has been removed from your car? Curious because both 993 & 964 manuals suggest the alternator should be mounted 90deg rotated clockwise from what your photo shows. Mine was the same as yours (wires exit straight down) but had an alternator replacement in its past.

Wondering if the manual is wrong or if there was a TSB / production change to re-clock the alternator. Seems like running the wires straight down would prevent the possibility of water running down them & into alternator but there must have been a reason for the note below to be included in the shop manual:

http://forums.pelicanparts.com/uploa...1350139840.jpg

edit.. took a closer look & the engine cross section drawing in the same section shows the B+ / D+ @ 90deg to the TDC mark (red arrows below):

http://forums.pelicanparts.com/uploa...1350145478.jpg

Ah, the good 'ol days before poka-yoke spread around the globe... ;)

Tom,
I just put them back in the same orientation they came out. From memory, I don't think there was sufficient slack in the harness to have done it any other way.

I do know that this one has been out before, for an engine overhaul.

Did you ever get an answer on doubling up the single row bearings? Wondering if anyone has tried this approach and where did they source their bearings.

Yes. It is important to make sure that there is no gap between the inner races. In other words, if the outer races and inner races are the same dimension in thickness, you won't have a problem applying an axial load to the inner race. Otherwise, with a gap between the two, you'd end up applying a side load on a ball bearing greatly shortening its life. Side loads on ball bearings, even deep groove ball bearings is a no-no.

Not a common bearing, but I did find a 17 x 32 x 7 sized single row ball bearing while searching once.

Thank you. I found that honda has a bearing (PN Honda 91006-MCK-A01) that is the 17X32X7 dimension. Funny that it goes to a gear shift mechancism off of a mid-nineties motorcycle about the same vintage as the 993.

On another note, Im having alternator issues on my 993. Battery fully charged and tested good at the LAPS. Crank the 993 and voltage drops to 11.9V (measured at the battery and the cigarrette plug).

Does anyone know if its practical to bench test the 964/993 alternator at the LAPS? I briefly looked at the tester while getting the battery checked and it seems to run off a belt. Seems like assembling a pulley back on the alt shaft may be an issue.

Without any diagnostic tool pointing me in the right direction, I was going to replace the VR and check the electrical connections on the alt backside. Any other components - diodes etc - that I can check while out? Id like to minimize the number of cycles of assembly and disassembly if bench testing is not an option.

One more note, my alternator has 8k miles on it - replaced a couple years ago - and was a replacement alternator from PCNA under warranty return. Im assuming that the slip rings are not worn out but I guess I cant assume anything with remanufactured alternators - even ones coming from PCNA. I dont suspect bearing issues since its still quiet - its just not putting out the proper 13V+.

This is the 3rd alternator in this car in 7 years of ownership. Im starting to think that maybe the 1-2 week intervals of the car sitting in the garage is too hard on the alternators as they recharge the battery while driving. Is it possible that Im killing the alternators because Im not driving enough? I dont use a battery tender most of the time because I drive frequently enough for the battery to start the car when I want. Maybe that is flawed thinking.....

Thats normal. In fact, the voltage if you looked at it on a storage scope would vary as the load varies during cranking.

A battery has internal resistance which is what you indirectly verify when doing a load test.

The condition of the cable and connections to the starter will have further voltage drops due to resistance which can only be kept to a minimum through the use of the appropriate cable and good crimps/connections.

Just install a voltmeter connected directly to the battery. While cruising, you should see at least 14V and preferably 14.2 to 14.4 V.
http://edelweiss.smugmug.com/Cars/Po...oltmeter-M.jpg

If the voltage is lower than that, you have an alternator problem, either a bad diode, bad VR, poor wiring/connections.

Note that you can get VRs with different set points. They are not all the same. The OEM VR on my 993 has a set point of 14.5V.

great article
thanks

1st step IMO = disconnect battery leads.
cheers

Craig

Great write up

Awesome write up. Subscribed

Hi SmileWavy

Many many thank's for explications and pictures http://forums.pelicanparts.com/support/smileys/clap.gif

Great write up. Be sure to disconnect the battery before you start

Just used this thread to remove, diagnose, fix and refit the alternator. The biggest problem I had was refitting the small fan shroud. You have to get the shroud to fit over the wire connector gasket and line up the four bolts. The problem I encountered was that there is limited room to manoeuvre (wires are connected) and the bolts can recede into the holes. So you are effectively lining up 5 items that can move.

I did the following:

1. Put a nut on one bolt and that brings the nuts up higher.

2. Disconnect the ground wires on the harness as that gives more room to manoeuvre the alternator

3. Line up the wire gasket first so it fits smoothly.

4. Carefully remove the nut and slide on the shroud.

5. Put a nut on any bolt with enough thread.

6. If a bolt recedes then tilt the alternator forward and give it a pat. Any thread showing is good as you can coaxx more out and put a bolt on it.

7. When you have all bolts on, then do them properly with the washers

8. Reconnect the ground wire and continue installation.

I'm doing the reinstall today or tomorrow, as soon as I can pick up my newly powder coated fan and housing.. Alt. rebuilder said the two rear bearings were totally dry, but that the fan hub bearing was still serviceable. I didn't know you could repack a sealed bearing, but he says he did, the ball bearings were fine and the race was fine too. So I'm reusing it. I'm guessing I will need to snad down the fan blade ends to clear the housing now with the new paint on them both.

Unknown to many is that sealed bearings come with a pre-determined (measured) amount of grease in them. According to the tribology department where I used to work, packing them with an amount other than specified (and I would assume fully packing them), shortens their life.

The bearings are very easy to replace since the alternator was already open. This was a bad decision on the rebuilder's part.
Be careful exposing the bare magnesium when you clean up the fan blade ends to clear the housing. Magnesium will oxidize and delaminate.
Good luck.