I seemed to have over researched this and lost my bearing so to speak...

My alternator bearing are at 131,000 miles and 40 years, so time for a rebuild this winter. I came up with a SKF number for the front bearing at YoYoPart

Front bearing #14 in diagram
BMW# 12311459278 = SKF  6203-2RSJ  

Is there a SKF number or equivalent in an affordable non-communist made bearing for:

Rear bearing #18 in diagram
BMW# 12311714521  ( Grooved ball bearing  12x28x12mm)

I came up with   BOSCH# 1120905003

Desperately seeking quality and decent value below dealer prices...no bearing houses nearby so something in USA via Internet is preferred.

63001.2RS is a sealed bearing measuring 28 x 12 x 12.

Super!  

That code, too much research, and this chart gets me into "novice class bearing cadet" now- cheers!

That's a handy chart, now saved for future reference.
Thanks.

Two Wheels Better wrote:63001.2RS is a sealed bearing measuring 28 x 12 x 12.

And it's as common as ....

Now that I have earned my "Novice Class Bearing Cadet" badge my search has uncovered a lot of good bearings at an unreal low price. They were all marked with the suffix "C3" which indicates loose fit. After reading about this rating in the Timken Engineering Bearing Manual it states these would cause wear on the shaft. I would use them on dolly wheels but will definitely avoid their use in my alternator. So "C3" is a no go.

Bricklayer wrote:Now that I have earned my "Novice Class Bearing Cadet" badge my search has uncovered a lot of good bearings at an unreal low price. They were all marked with the suffix "C3" which indicates loose fit. After reading about this rating in the Timken Engineering Bearing Manual it states these would cause wear on the shaft. So "C3" is a no go.

My reading of the Timken manual indicates problems start happening when clearances are larger than C3. It's possible the C3 could fail under preload, but our alternator bearing just gets beaten into position and then everybody goes out for donuts. Preload isn't a thing. I'd call C3 a go and sleep soundly; of course, it isn't my alternator. 

From p.85 of the manual (I added the bold font) :
Most applications use a normal or C3 clearance. Typically, larger clearance reduces the operating load zone of the bearing, increases the maximum roller load, and reduces the bearing’s expected life. However, a spherical or cylindrical roller bearing that has been put into a preload condition can experience premature bearing damage caused by excessive heat generation and/or material fatigue. As a general guideline, spherical and cylindrical roller bearings should not operate in a preloaded condition.


There are several pages listing C3 bearings in multiple manufacturers' alternator applications within this bearing manufacturer's catalog—an example that seems to corroborate what you also have found. Despite my not being a Cadet, I wouldn't be skittish about using a C3; I'd be selective about its manufacturer or vendor. I found one for 19.50USD and if I needed one, I'd probably get that one just for the adventure.

Dai wrote:

Two Wheels Better wrote:63001.2RS is a sealed bearing measuring 28 x 12 x 12.

And it's as common as ....

Hens' teeth?

Alas, it's in my best interest to drop out of bearing school unless I read different sources and/or the entire manual.  ;-)

In closing I found a better explanation for "C3" and will zip my lips and just order some bearings and make a go of it!  

"Some bearings are available with more or less important variants (high or low internal clearance, special grease, very high temperature, etc.). These variants are systematically indicated by prefixes and suffixes in the part number.
For example, the suffix 2RS means that the bearing is splash-proof, thanks to a sealing flange on both sides of the bearing.
The suffix C3 means that the bearing has increased internal clearance, and will require a higher operating temperature, or a higher rotation speed. "

Source

Bricklayer wrote:...
The suffix C3 means that the bearing has increased internal clearance, and will require a higher operating temperature, or a higher rotation speed. "

Source

Your source got that part wrong. C3 withstands higher operating temperatures and higher rotational speed.

The C3 in the product name means that this bearing has a higher (internal) clearance than normal. The C3 clearance is most frequently used for this type of bearings. The extra internal clearance allows expansion due to high speeds or temperatures.

My source: https://www.abf.store/s/en/bearings/6206-2Z-C3-SKF/228150


A tighter tolerance than C3 would not work for crankshaft main bearings, for instance.

Bricklayer wrote:Alas, it's in my best interest to drop out of bearing school unless I read different sources and/or the entire manual.  ;-)

 I . . .will . . . order some bearings and make a go of it! 

Don't change horses in the middle of a stream, Bricker. It confuses the new students. 

Regardless, there's likely to be somebody on eBay willing to buy your Cadet badge and patch if you're concerned about being accused of stolen valor.