For 6-cylinder, you can rebuild your Bosch Alternator for $30!!!
I am gathering information for us 6-cylinder owners to tackle this Alternator Rebuild and do a quality job. So feel free to add info if you know of any good suppliers out there.
I called around, as it turns out many rebuilders in the US put in cheap Chinese bearings, no wonder the Bosch Alternators fail again in a few years. There are a few suppliers that sell rebuild parts to the majority of rebuilders throughout the US. And each rebuilder rebuilds the Alternator his way: you may get only new brushes, the old bearings may receive only grease (instead of being replaced). So when buying a rebuilt alternator, you are at the mercy of the rebuilders, whether it is sold at Autozone or online vendors.
Unlike other previous Bosch Alternator, the E39 Alternator uses a larger FRONT bearing 17x52x17mm type (this bearing takes a lot of pulling force from the drive belt, so they made it bigger to last longer), but this creates a different problem (see below).
Finding this larger bearing from a quality maker like SKF or Koyo is very very difficult (I have not found the supplier yet), so you may have to settle for Chinese bearing, which “might” be OK because Chinese bearings are a “hit or miss” thing, the Quality Control is spotty, some Chinese companies are very good and some very poor. And you don’t want to take your alternator apart in 1-2 years to replace the front bearing. So if anyone knows a source for quality FRONT bearing, please chime in.
Reputable bearing makers are:
- SKF (USA)
- Timken (USA)
- Koyo (Japanese)
- Nachi (Japanese)
If you do the Rebuild yourself, you know you will do a quality job. The Bosch rebuilt alternators at Autozone are probably OK, but 99% of the time, they use cheap Chinese bearings, which may be OK but may not last as long as factory alternator.
Time to study the Typical Bosch Alternator anatomy! In fact most alternators, whether it is Honda, Toyota, or whatever car, have the similar setup. If you have not slept through your high-school Physics class, you probably understand how a typical alternator works.
Take you time and go through this excellent Rebuild DIY for a Bosch Alternator in a Range Rover, the E39 is slightly different and I will discuss below:
For 1998 528i (or similar models), the Alternator is:
- 120A Alternator
- Bosch 0 123 515 022
- BMW 12 31 1 432 986
A very good source for technical data is a company from the UK company Wood Auto:
All you need are:
1. Set of Carbon Brushes for $5:
- The whole Rectifier assembly is Bosch 1127319712 ($50 on ebay). If you buy this whole assembly, you don't need to buy the brushes.
- But a set of good carbon brushes is good enough because the rectifier rarely ever goes wrong. Brushes are Bosch 1127014028. Just undo the old brushes and install new brushes, you may have to solder them in the existing rectifier assembly.
Voltage12; Depth 3.9; Width 5.9; Length 16.
In the US, you can get the brushes from Wagner Alternator Supplier (PN W030-03K). The bearings they carry are Chinese (they told me! Anyway this is what you get when you buy a rebuild Bosch Alternator!).
2. Small REAR Bearing 6203-2RS:
(2RS means “rubber seals” on both sides).
This bearing is very standard for Alternators: 17x40x12mm.
Search ebay, amazon etc. you will find some people selling SKF or Timken bearings.
Your local bearing store should have this.
3. Larger FRONT bearing: 17x52x17mm:
Bosch PN 1120905012 or B17-99:
You can easily find this for $9 at Bearings Direct:
If you don’t mind using Chinese bearing for this part then go ahead, I still have trouble locating this particular bearing part using a reputable bearing makers mentioned above (SKF, Timken, Koyo, Nachi etc.), so any info on this particular bearing is appreciated!
Last edited by cnn; 05-08-2010 at 07:20 PM.
Such incredible work CNN!
Please review my thread: http://www.bimmerforums.com/forum/sh...o-Improve-Ride
Thanks Cam! Nice write up!
Anyone try this renewal on a 540i water cooled alternator?
I'm up to try if I can locate the parts...
1999 540it - Schwartz II/Sand Beige, style 5 rims, Conti DWS 235/45 tires, Billy HD/Sports, Stoptech S/S BL, F1 Pinacle 35% tint, Zionsville Cooling kit
1998 318ti Cali Sport - Schwartz II/Schwartz Anthratz, staggered style 23
1997 318ti Sport - Schwartz II/Schwartz Anthratz, staggered style 68 ,
1995 318ti Active - Alpineweib III/Schwartz, squared style 32
1994 325i - Bostongrau/Tan, Billy Sports, H&R springs
1991 318ic - Schwarz/Anthratz Stoff, Bilstien HD, Z4 3.0 SS, Magnaflow, S/S Stress bar, x-brace, M20 FW, Elipsoid/HID, K&N
1995 318ti Sport Schwartz II/Schwartz Anthratz - Sold
1985 635CSI - Schwartz\Sand - Sold
1984 533i "Max" - Schwarz/Schwarz, - Sold
1984 318i - Champagne/Tan, Stock - Sold
Great write up, but what are the symptoms of an alternator in need of a rebuild?
Of course no battery charge, but would lower amp out put or something also be a cause?
very nice! This needs to be added to the DIY section
The 2 bearings are the same as I6 engine. This is a beautiful DIY for V8 water-cooled alternator from E38!!!
BMW die-hard Fan Rejoice!!!
I just spoke to Dave at Smith Co Inc. Alternator Rebuilder in Greely Colorado (Contact Info is below).
Good news if you want to rebuild your alternator to factory spec!
As I mentioned above, a typical rebuild Bosch Alternator you find at Autozone or online:
- Chinese bearings x 2
- New Brush Holder (HUCO brand, made in Germany)
Dave told me in theory you can undo the old brushes and put in new brushes, but the Regulator assembly has a circuit board that is solid state. And even solid state circuit board can only handle so many million cycles, and they can go bad. So Dave recommends replacing the Entire Brush Holder instead of brushes alone (Brush Holder = Regulator + Brushes)
So I recommended Dave to list all these items on ebay for us, so we can order all we need from a single source.
1- FRONT Bearing 17x52x17mm:
- They currently list a Chinese bearing now for $29.99.
- Dave will list the Bosch OEM bearing (likely Koyo brand) with picture on ebay for $39.99.
2- REAR Bearing 17x40x12mm; 6203-2RS type:
- They list a Chinese bearing $6.95.
- Dave will list a quality brand (? SKF, F.A.G. etc.) soon for about $8-10.
- If not you can easily find this bearing on ebay by searching: "6203-2RS" and scan the ebay search results for brands such as:
F.A.G., SKF, Koyo, NTN.
3- Brush Holder for my year 1998 528i is: 8020-1172.
- Made by HUCO (Made in Germany).
- Will be listed on ebay for $59.
There you go, if you want factory Bosch quality.
RE Slip rings:
I just spoke to Dave @ Smith Co Inc again.
Bosch Alternator slip rings are very good and after 100K miles, all you need is to smooth it up using 3M emery cloth or very fine sand paper to shine it.
No need to replace the slip rings.
Smith Co. Inc.
530 11th St.
Greeley, CO 80631
Phone: (970) 353-3121
Ebay seller name "smithcoelectric".
Last edited by cnn; 06-03-2010 at 03:19 PM. Reason: Automerged Doublepost
Cool! Thanks for the link. I'm in the middle of rebuilding my M54, and rebuilding the alt & starter just make sense at this point. Especially that hard to get to starter.
I spoke to Dave at length today. Very nice person. Seems like a very honest shop.
They have been rebuilding starters, motors for years (maybe since 1985) but only go online recently.
They know their stuff really well.
So call Dave for anything you need. They carry standard stuff and OEM stuff if you ask for OEM stuff.
When in doubt, give them your car/model/year they can look up what you need.
Last edited by cnn; 06-03-2010 at 08:39 PM.
"I'd smash that (Jennifer Connelly) like a failed coup in sub-Saharan Africa."
~Macktheknife in my epic Jennifer Connelly OT Thread
Just a small update, in case someone wants to DIY the alternator.
Note: This is mostly for the Bosch alternator rebuilt [two weeks ago I helped rebuilt my friend's alternator on his BMW and his car was equipped w/ Bosch alternator].
We didn't changed the AVR [Automatic Voltage Regulator] or some called it Rectifier, also the brush was still in good condition. After the rebuilt and installed it back, we've got 14.2 volts and it's running fine.
To find for the smaller bearing/s brand Nachi [Japan made bearing], you can search Amazon. But for the larger size bearing and pretty hard to get in the USA, below are the links:
For bearing size 17x52x17 --> KOYO bearing 83B218 from Simply Bearing in UK and delivery took about 7-10 business days. We ordered it from them because we insisted to replace it with Japanese bearing and we strongly refused using Chinese made bearing!! The smaller bearing we got it from Amazon, Nachi brand but we forgot the bearing size.
Or if you want to order it straight from US online store for the 17x52x17 size bearing but it only says OE Bosch bearing [don't know where the bearing was made from] --> Smith Co Electric
For the hand-tools to remove the pulley off the alternator:
Generator pulley wrench, 24 mm hollow thin socket [part # 83 30 0 491 167] and Samstag shipped the tool really fast --> Samstag
And CTA Tools 8088 Bosch alternator wrench [ref. from another from E46 Fanatics, member Safar with how to use the 24mm hollow thin socket & the CTA 8088 tool] from --> Amazon
By the way, you need a 3 jaws puller and a couple of pretty big size deep socket --> here's from --> Wheeler Dealers, where Edd showing an alternator rebuilt on a BMW M5.
** Then... last but not least, if you don't want to do your own alternator rebuilt, then you can get it from AlternatorPros, but you have to guess yourself with what kind of replacement parts the rebuilt alternator [bearing/s quality is in question, though??].
Last edited by dbiMMer10; 06-19-2012 at 08:42 PM.
I just wanted to bump this up to point out that the 1997-1998 E39 540i air cooled alternator uses the same bearings as listed above.
Triodiode is where I got my front bearing, it's a Japanese NTN branded bearing. I had to look hard but I found something from a reputable manufacturer.
The 540i brush dimensions are also the same, and we can get new slip rings off of ebay. Mine was worn enough to justify replacement. Hopefully this helps someone.
Last edited by 240sxguy; 10-17-2013 at 09:24 AM.
Since it's bumped, I might as well add a few corrections.
The 'brush holder' assembly is not the rectifier, it's the voltage regulator. The rectifiers have to handle lots of current, while the voltage regulator only handles a tiny control current.
An automotive alternator creates its output power in the outer stationary coils. The generated power is AC and is converted to pulsing DC by big rectifier diodes. The diodes are permanently mounted inside the alternator on a heatsink plate. A typical BMW alternator will have six primary diodes and six secondary diodes. Each primary rectifier diode must be able to handle the full output current of the alternator, 90 to 120 amps.
The spinning rotor creates the changing magnetic field needed to generate power. It takes only a tiny amount of power fed to the rotor's electromagnet to create this field. The voltage regulation is done by controlling the power fed to the rotor. Since the voltage regulator only needs two input wires, and the output is two wires to the brushes, it makes sense to combine the brush assembly with the voltage regulator.
Well, it actually made more sense decades ago when voltage regulators failed about as commonly as brushes. About 30 years ago they put the voltage regulator onto a single IC and figured out most of the failure modes. It's now extremely uncommon for the electronics to fail. There isn't any wear mechanism. They'll age pretty much like window glass. It's pointless to replace the voltage regulator based on "millions of cycles", thinking that it somehow isn't as good. The only reason to replace the assembly is because the brushes are worn out and it's a PITA to solder new brushes in place.
Last edited by djb2; 10-10-2013 at 06:16 PM.
Sorry to bump such an old thread, but I think this question is inline with the reat of the thread. I have a dying alternator. Tests good on the testers, but once it's on a car and running for awhile, as temp goes up charging voltage goes down, down to a point where it's not charging at all anymore. Would this be an internal problem of some sort, or just a bad voltage regulator?
Have you checked the brush length? It's possible that they aren't making contact after the alternator heats up.