Anybody replace alternator bearings?

[bherman13]

I've got a new (used) 120A alternator that I'm getting ready to put into my car with a new clutched pulley and new voltage regulator. I'd been thinking about putting new bearings in this one since the bearings in my old one failed and turned it into a paperweight.

In my research, I've found the sizes are 6203 and 6303, but I haven't found anything else regarding other statistics. The thing that particularly concerns me is max rpm.

Anybody have experience with replacing alternator bearings? Which ones did you buy and where? Is it difficult to replace them?

It's proving very difficult to find the right bearings. Yeah I could buy any sealed 6203/6303, but according to my findings, our alternators spin over 3x as fast as the engine and I don't know enough about bearings to know whether ones I'm finding can handle those speeds. I'm starting to think I should just leave them alone.

 

[Digital Corpus]

I've replaced the slip ring and one of the bearings on one of our 2 alternators in our B4's. Once I'm sure it's staying alive, I was planning on making a tutorial when I replaced them on the other alternator.

The slip rings I purchased through Amazon, but they're still sold through Maniac Electric Motors. Looks like you can pick them up through ebay.

The *one* bearing I replaced, and since I did not pull the pulley I do not know if they're the same, I measured and replaced with this one from ebay. So far, no problems.

 

[Clatta]

Haven't done it on the TDI yet but I have always repaired my own alternators and starters with bearings, bushings, brushes, regulators, diodes and starter drives. I go to a local alternator repair shop for parts. Some shops are a little reluctant to sell parts but they almost always do. Real repair shops are getting harder to find.

Good luck, I still feel like it is worth the effort. If you take a known reliable unit and renew the wear parts it makes more sense than getting a rebuild with an unknown history.

There are a few gotchas on some units. Check beforehand if soldering is required or if you need a pin to hold back brushes or whatever.

 

[bherman13]

I believe voltage regulator is pretty simple. What I don't know about is if bearing replacement is relatively straight forward. I'd probably stop if I found something that would have to be soldered.

When buying a new bearing, did you ensure the speed ratings would be adequate or just assume that a standard sealed bearing of a decent brand would work?

 

[Chris]

The 6203 is probably the most popular bearing size in existence. 6303 is still very mainstream.

Most bearings make noticeable noise as they go bad. If the alternator's reasonably quiet as it is, I wouldn't bother to swap in new bearings.

Assuming you manage to remove an old bearing, the key is to not axially load the new bearing as you're pressing it in. In other words, don't press against the inner ring to get the outer ring into the housing. Don't press against the outer ring to get the inner ring onto its shaft.

 

[bherman13]

Well since this has been a slow going overhaul, I'll fill you guys in on what's happened.

I went to an "Automotive Electronics" shop here in town and asked them about the bearings. The guy says he can sell me "alternator bearings" in sizes 6203 and 6303 (the correct and very common sizes for this Bosch alternator). I asked to confirm they have a high enough speed rating, to which he replied "Well, they're 'alternator bearings', so yeah." I figured for $15 total, it was worth the shot. They were an off-brand that I did not recognize, so I did the research on them.

I have found that no matter what brand, the bigger bearing has the slower speed rating. That makes since, of course, due to more weight and whatnot. Well, the 6303 bearing that he gave me has a max rpm limit of 11,000 rpm. Not really enough when you take into consideration the pulley size differences and the red-line on the 1Z. The way I calculated, I would need a bearing that could withstand 15,900 rpm when the engine is at red-line. *Disclaimer: If my engine ever sees red-line, it would only be briefly... but I do like the peace of mind of knowing the components can withstand it.

There is a place called "Bearing HQ" about a half an hour from me that I decided to check out. They're not an automotive shop or anything, they just manufacture/sell bearings of all types. I asked them the same question; "Is there a difference between bearings used in alternators and regular sealed bearings?". To his knowledge, no, there isn't. So he went and grabbed a bearing in each of the correct sizes and brought back the book to look up their speed rating.

He came back with NTN branded bearings and in the book it listed 6203 having a 19,000 rpm limit and the 6303 size having a 16,000 rpm limit. Finally! A sealed bearing from a name brand that has the right speed limit.

So, since then I've been working on getting the bearings rebuilt. I had to pause for a bit while I looked for a way to get the large bearing pressed out of the front face. Once removed, I was able to cut both bearings off (which was a p.i.t.a.). I couldn't get a puller in behind the bearings since the clearances are too tight, unfortunately.

So right now I'm ready to start reassembling when I got to thinking about replacing the slip rings while I'm at it. Mine look like they're pretty worn down so since I don't want to have to take the alternator back apart again and replace them in the future, I went ahead and ordered some from the links Digital Corpus gave. I ended up going the eBay route since it's a couple bucks cheaper and the shipping is better. Just so other people know, how long did it take to ship through Amazon?

Once I'm sure it's staying alive, I was planning on making a tutorial when I replaced them on the other alternator.

So now I'm at this point. Were you still planning on making that tutorial? The way I'm thinking it goes (just from looking at it):
1) melt the solder joints off the slip rings
2) remove slip rings straight up
3) insert new slip rings
4) re-solder the wires on

Any tips you want to add to this, DC?




A couple final thoughts:

I figured out why the "rebuilt" alternator that came in my passat failed so soon. They used a shielded bearing. Shielded bearings have a metal seal instead of a rubber seal that does not completely seal off the bearing. They can spin faster due to less friction, but they leave the necessity for cleaning and re-greasing. Grease can get out and dust can get in and that's a recipe for a failed bearing.

The bearings in the used, not rebuilt, alternator I purchased from one of the classifieds (either here or vwv) were sealed. The large one was a Koyo, and the small one was an NTN. I don't know for sure that those are the factory bearings, but they're both a name brand sealed bearing and the alternator did not say "remanufactured" anywhere. Just thought you all might like to know that information.

 

[30_Yr_Dsl_Veteran]

My son replaced them on our '98, but noise was no different!

 

[Digital Corpus]

I've not had time to make the tutorial. The rebuild I previously did, which replaced the rear bearing, is holding up with not problems. It seems that by fluke I picked up the right bearing to begin with too.

Your procedure is accurate. Just so you know, I had to get a jeweler's flathead involved when desoldering the slipring. It seems that the airings are mechanically pressed onto the ring and then soldered. While I held the iron on the wire, I pried it away with the screw driver.

As for pressing off the slip ring, go grab a 6mm, 3/8" drive socket from a shop. It'll fit through the top of the slip ring and press on the spindle making it possible to use a puller.

Be careful putting the slip ring back on. It's possible to press it too far on. The first one I did in on about 1mm too far so the brushes are not centered on the terminals, but they are still in the contact area without going over the edge.

 

[Chris]

Pretty amazing that someone would use shielded bearings for that application.

Sounds like you've made good progress!

 

[30_Yr_Dsl_Veteran]

Pretty amazing that someone would use shielded bearings for that application.

Sounds like you've made good progress!

 

[bherman13]

Yeah, it's been slow going. It's kinda been a side project to work on when I get a few minutes. Just made the biggest progress by getting the old bearings off. I wish I had stopped to take pictures, but I've never been good at that. I've considered using those other bearings I bought to rebuild the j/y alternator that I'm using in the meantime. Maybe I'll take some pics and make a write-up if you guys think there'd be enough interest to make it worth my time to do a rebuild.

This has mostly been a learning experience for me. I knew next to nothing about alternators before I tore into this one, but I tore into my failed alternator first to see what the inside looked like.

Thanks for the info DC!

 

[machinist]

Bherman nailed the bearings. Slip rings can be turned to get a good surface, minimum diameter should be in specs. Be glad it's not a generator-after cutting the comm the micas should be undercut to prevent carbon bridging (should do this on starters too).

 

[0die]

did it once on an old jeep I had. got a "universal" GM bearing/diode/brush kit from pep boys or somehting like that mailed to me...easy job.

had to do it when I lived overseas in pre-ebay times...kinda hard finding american parts on a greek island.