1984 12SI Alternator Restoration

Why? Because I can.

I have leftover pieces parts from the 85 rebuild, so rather than let them go to waste, I figure I'll just go ahead and buy a few more sundry items and run the gambit on rebuilding a mid-year 1984 78A alternator as well. This is the alternator which was on my 84 H/O when I got it. It wasn't even made until after the H/Os were built that year, so I know it isn't the original. I won't be replacing the rotor and stator with new, however, as I cannot find any NOS ones. But the rotor/stator checked out fine electrically on the 85 original pieces with 60K miles, so I'm rolling with those. It won't be quite as detailed as the other thread, but again, there will be comparison pics done. I've got almost $300 in the restoration of the other one, but that was including the big bracket and prepping/refinishing the fasteners too. So far, I'll have MAYBE $110 bucks or so give or take on this one. We'll see which one turned out better looking.


I tore down the 84 unit to parade rest:



And these will be sent out for cleaning/blasting. Now, before you get your panties in a wad about blasting aluminum, the main point of this exercise was that I let someone else do all the refurb on the case last time. For what he charged, plus getting his stodgy attitude for free, I suppose, I figured I'd try this out myself for a LOT LOT less. Granted, I had some fasteners cleaned and plated as well at the time, but I'm still saving a ton. Plus, I have the "AR" stamp already...

The casing is being sent to a guy that does "vapor honing" or basically, water blasting with fine media. The process "seals" the metal so you don't necessarily have to hit it with clear or anything, and no residual media is left over, nothing to clean up really, and it's really a great way to go with aluminum because it's super-gentle on the soft metals. And, for about $65 (includes shipping both ways) for getting this alternator case done...well worth it IMO. It's going out in today's mail.

Examples:
Corvette aluminum valve cover started with the process:


Top cover vapor honed, the bottom two are NOS right out of the box:


Looks pretty good.


And the Corvette alternator case...I was sold.




We'll see where this ends up.

Holy Jesus! USPS must've heard me talking about them. Ok, probably not. But check this. On Tuesday morning, 2/18, I mailed off my alternator casing halves to the vapor blaster. There's nobody near here except in Florida or North Carolina. So I was shipping it either way. There's supposed to be a guy in Atlanta but I couldn't get hold of him.

Anyway, for whatever reason, it made it to the shop I shipped it to late on THURSDAY afternoon, 1/20. I got an invoice today, paid it, and it's back in USPS's hands of of today 2/21 at 10:51 am ET. My head is spinning. I know an alternator case shouldn't take long to blast, but friggin' wow! That's ultra-fast service. I'm stoked to see what it looks like. The one piece I didn't have and is on order as of Tuesday won't even be here until early next week, but dayum. That was fast turnaround. Communications with the owner was great and emails must go straight to his mobile because he usually answers any question within minutes.

Anyway, if it turns out good, I'll disclose the name and contact info. Well, if it sucks I'll do that too, just so people can avoid it. Either way, I'm still floored that it's already on its way back to me.

While I'm waiting for the now-clean alternator casing to get back to me (in Atlanta USPS processing at the moment), I started putzing around looking at bearings again. I know a lot of people will just swap out an alternator or starter or other component due to ease and time. That's perfectly ok, too. Read no further. I'm simply not afraid to take junk apart. If something goes fubar, I'm still covered with the spare parts. I'm not a master G-body mechanic, but I think I can maybe play one on TV. So I did a little deep-dive, but not too deep, about more bearing junk.

I've asked several people (apparently they're not lubrication-specialist engineers) and never got a straight answer as to a suitable bearing lubricant should you ever decide to re-lube an alternator bearing. Reason I say this is that although the 80s 12SI alternators had double sealed bearings in the drive end (front), they also have needle bearings open on one end for the slip ring end (rear). Plus, some of the older alternators have open ball bearings with no attached seals. They use an archaic system of felt and slinger shields. Luckily you can simply replace them with a 6203 double seal bearings as they're the same size otherwise if you don't want to restore it to absolute correctness. Nobody would see it anyway. But sometimes the bearings are just fine, and I'm not sure why you couldn't relube a bearing vs. replacing it every time. It just depends on how confident you are about your abilities and how fat your wallet is, I suppose. Based on NTN information, 30-40% full on a roller bearing capacity is fine. You don't need to pack the pee out of it. I've even seen on a different car forum take the shields off a 6203 "sealed" front wheel bearing and clean it out and "repack" it due to the original grease solidifying inside the bearing instead of having to purchase the entire front hub unit.

NTN made a butt load of bearings for our cars in the early 80s, as Delco/New-Departure-Hyatt (NDH) basically went away in 1986 for supporting the auto industry, although they still made some aircraft bearings. Every alternator bearing I've ever seen in the 12SI's were made by NTN.

Although NTN manufactures all over the place, it's not hard to find older NTNs made in Canada, Japan, and the USA, to which, I'd gladly trust any NTN bearings from those places. One thing I do like about NTN bearings is they have a catalog to tell you WHAT sort of lube comes in their sealed bearings from the part number. Sometimes part numbers don't mean anything, but for the bearing industry, they do. The chart below shows information from I believe the 2011 catalog, so it could be a bit out of date.

Unless you need a really tight tolerance, most electric motors tend to use a C3 clearance classification. This is for thermal expansion and keeps heat build-up to a minimum. They're not sloppy. They're just a microscopically tad more ball clearance.

Once up to operating temps, no issues. The limiting factor on these sealed bearings is the grease. Most all the 6203 bearings are up to 18,000 rpm rated, but with the dual contact seals, it's typically limited to sustained 12,000 RPM, depending on the grease. Certainly should be able handle the alternator duties alone on your stock vehicle. Most alternators idle in the 2K rpm range. After you hit the 6-10K range (alternator RPM), most alternators are maxed out anyway as far as charging output. This is just a generalization. Beware of some of the bearing sellers advertising 19,000 rpm, etc., because you need to check the manufacturer's information to determine the exact limitations.

Looking at the chart below, you can see the 6203 basic p/n. Type/series/bore is 6203, which happens to be the size needed for the 10/12SI alternators drive end and front A.I.R. pump bearing. The rubber shielding basically comes in two types, contact and non-contact. And the 6203 comes in various shield combos from no shields to one on each side. This is designated by "L" (one side shield) and "LL" (both side shield). Rubber contact seals have a larger lip seal around the center carrier of the bearing, and while they do take a hair more torque to turn, they're excellent at sealing out the elements. NTN bearings use a "U" (contact) or "B" (non-contact) to designate this in their seal/shield portion. By all means, the alternator bearing will live longer with the "U" spec. Other bearing manufacturers may use "RS" or "2RS" to indicate the "rubber seals".

When it comes to lube, there are two poly-urea lubes that can be derived from the suffix in the chart below. One is "5C" and the other "L627". This indicates Chevron SRI #2 (5C) and Exxon Polyrex EM (L627). The Chevron stuff nowadays is known as Black Pearl SRI #2. Interesingly, it seems the consensus from many HVAC repair techs these two particular greases are the go-to's for them when re-lubing motor bearings. The greases are excellent for their intended use, doesn't migrate along the shaft which would muck up the brushes, and is "electrically safe" whatever that means. Less of a fire hazard I guess. Even more interesting, I read that Amsoil doesn't recommend any of their greases be used in alternator bearings. Hmm. Anyway, Chevron or Exxon polyurea grease is plentiful and cheap, around 10-12 bucks per tube.

But they have one more suffix they don't list in the chart that I've seen where the lubricant suffix information is, "EM", and has some speculative aura about it. From what I can gather, I believe the EM suffix means it's designed for "electric motor" use?? This would roll right up the alternator's alley as some people have stated bearing manufacturers use a form of polyurea grease for factory-fill lubrication on alternators. Although I still cannot find the type of grease for EM, I'm assuming it means an "EM" bearing is filled with SOME sort of polyurea grease from the factory, although it's not specified to a brand. It could be a new designator for Exxon Polyrex EM grease perhaps? Makes sense as the alternator is generating power vs. using it that you'd want a polyurea grease. One seller website lists the EM and L627 under the same ordering part number comparable to the L627. Not sure if there is any factual info to prove it, though.

I have purchased and installed the GM p/n drive end bearing for the 85's alternator, so I'm confident that is the correct bearing for the application. But with the 84, I'm not going to spend a buttload of $ on a GM-boxed NTN when I can use pretty much the same exact bearing that comes with the correct type of grease installed for much cheaper.

So, based on what I can find out so far, I have purchased 6203LLUC3/L627 bearings, the ones with Exxon Polyrex EM grease. And as far as re-greasing rear bearings, if I ever did, I'd use either the Exxon or Chevron SRI #2 grease. But that's me. If in doubt, use the GM part number 908419.





And here's another chart of lubes from their 2020 product catalog online. Again, a few years behind. If I type in a search for 6203LLUC3/L627, it keeps popping up with an EM suffix bearing, so there may be something to it. But also, it comes back with another one with a suffix of LY35, to which I still haven't figured out what that is, yet.

As usual, USPS finds a way to stall things right at the goal line. I should have got the casing back on Monday, but eventually I did get the casing halves back Tuesday evening. Why so late? I dunno. Regardless, that's basically 1 week for turnaround back in my hands. Pretty good for mail-order personal service.

Anyway, they came out much better than they went in, and I'm very happy with the results. Details were retained, and vapor blasting seems to be the most gentle on the aluminum. Note the details on the lettering and casting marks haven't been eroded away. Very happy with the outcome. I can only recommend his services based on what he's done for me and my own interactions. There's always the possiblity that I'm a lone outlier and got great service? Maybe. But I doubt it. The guy doesn't know me from Adam and I ambushed him with an email and some questions and we went from there.

They were done at:
A.O. Customs
336 Glenroy Ave.
Cincinnati, OH 45238

by Shaun Werning, to who I am guessing is the owner. VERY attentive to emails and communications. It's what I consider reasonable rates.

[email protected]


As a reminder of the cruddy casing I sent in:


Compared to the freshened up one.



Note the detail areas aren't eroded, even the bolt hole threads.



Anyway, he can vapor blast just about anything. And he does other stuff too. Contact him for any questions/concerns/potential services.

As usual, buying GM/Delco old-school parts for the project is almost never a bad thing. I trust them. The other brand stuff, or even the newer "off-shore" (China) Delco crap isn't included in this discussion. You want to use it, fine. But if you do want to use aftermarket, I believe I'd be more trusting of the OLD-SCHOOL NAPA and Standard Motor Products stuff. The older stuff seems to be pretty reliable if memory serves. I've had to use stuff in the past.

Also, ran across a video of a 10SI (virtually same as 12SI with MINOR differences) rebuild. Pretty decent, although I don't agree with his leaving the slip ring end bearing (rear) sticking out a little. Claims the rotor won't hit the back of the bearing cap. As designed, it won't be a problem when you install it as GM intended- FLUSH with the boss hole. GM did it. Why not continue what works? If it's done right, the collars and everything as well as the front nut holds the rotor to the FRONT bearing anyway. Tightened to spec, it's kinda like using solid pinion sleeve instead of a crush sleeve in the rear end. It's locked and isn't moving fore or aft. This allows full roller engagement on the rear of the shaft along with a slight gap in the back. No need to leave the bearing extended out.


Anyway, on with the show.

Bearing ready for press-in



Got to make sure to cover the bearing open end as it comes pre-lubed.



A bunch of old-school parts.



(almost) Ready for the stator. EDIT: To add that this pic doesn't show the terminal stud package now installed for the 12V wire before stator went in. It's installed.

Testing Data. Everything checks out good per CSM checks.