Another alternator hits the dust and not under warranty

Oil may be cooling it, but it's not coming from the rotor, that's for sure. Oil does not fling inward off a spinning object.

Unless BMW defied the laws of physics.

Sorry, but the stator is on the outside of the rotor.

Hey the Germans do that all the time ...

But ... let's suppose there is oil on the inside surface of the flywheel ..........
(in the "counter-bore" where the stator sits ... )
the clearance between the poles of the stator and the inner bore of the flywheel is only a few thousands of an inch .... I think...........

If that's true and the oil film is more than a few thousands of an inch thick then the ends up being "scraped off" and being flung around?

I don't know ... I'm just talking while .......

Sorry, the rotor surrounds the stator in this case, so technically, it's 'outside'.

I'm just speculating too, but the design of this alternator is kind of interesting, the way the rotor is attached to the crank in a reversed way from what most alternators are, with the stator fixed to the inside of the outer crankcase cover.

This leads me to believe there's no oil feed to the unit aside from whatever might be in the side cover.

Of course, this design makes it extremely easy to replace the stator since unlike most designs, you don't need to pull the rotor first. A real advantage, in this case.

We'll probably buy another $100 stator to bring along on trips, since it's so easy to replace, and you can even do it at the side of the road if necessary, as some people already have.

I believe you are correct
i.e. there is no pressurized oil feed.... the only oil that would enter is oil that that does so more-or-less by accident, based on spray, general oil level in the side cover or etc....

There is a Buell derivative design of this engine that does apparently spray oil into the stator area from the main crankshaft journal ... but we are not that lucky..............

Yep..I think most of us have been over using the "oil cooled" term too much.

The stator is inside the rotor, and there is some oil (not under pressure) in this housing to provide lubrication to starter gears, etc. This oil likely distribute as a mist because of the air turbulence generated by the spinning rotor around a very un aerodynamically smooth stator. Looking at the new BMW "fixed" stator it is clear they added specially crafted holes to enhance this air flow in and around the stator.

It would be easy for me to accept that the primary cooling on this stator was air with primary cooling coming from the external housing surface. The would be some cooling from the oil mist...but how much I have no idea.

Oil does have a much better heat transfer coefficient than air.

I too think this design is both clever and cheap. Using the rotor to double as the flywheel is neat, have the stator fixed on the cover makes fab simple and replacement easy.

where BMW fell down is thermal management....and the seaming limits of available epoxy potting that meets the spectrum of operating criteria.

After a brief look and what seems to be a thriving business of replacing stator and the like, BMW is not alone in this error.

Just had another thought

We've been complaining about BMW only selling the upgrade stator with an new rotor/flywheel for $900.
Has any one on this site looked closely and the new rotor/flywheel? Have that added any "fins" or other devices on in to improve air flow/circulation / cooling.

If there is maybe that is why they only sell as a pair?

I believe vtbob is correct, or at least I agree. I took JrWoody's hint, picked up a dozen tall cans and read through most of the posts here while the GF slept through her movie.

There just isn't enough oil flow to be effective. no spray nozzle, no oil slinger or oil submersion really. In any case, further debating won't change things. My attitude with this particular BMW is that it's relatively easy to fix. Being an Aircraft Mech, I appreciate that. Also the reason we bought the GS twins over our old singles. Oil change, easy. Clutch, not so bad, stator easy (not rotor), wheel bearings etc. Yes it's bad quality or poor design but hey, it's the Devil I know and I can prepare for eventual part failure. At least we have aftermarket choices for parts. I'll buy three stators before I'll pay the grand for an assy.

As far as BMW's not selling separately, it's marketing and cost cutting. Easier to stock one PN assy then all the little bits separate. Forecast market needs and then end up with a highly unbalanced stock of alt parts. For what BMW makes on one stator itself, they probably give that tiny profit to the aftermarket. Without generalizing, and having worked for Motorrad here, a lot of owners have more money than technical ability or even interest. "Do what it needs". I've seen it many times. I mean, does anyone take their GS offroad? (2%?) Why build it tough?

Truer words were never spoken.
Though you are being a little bit harsh, I will bet it is more like 8 out of 10 GS owners never take their bikes off road.
Out of the other 20%, it was likely about 75% only road to a campsite or on a connecting fire road because they had to.
Then the from the remaining 25%, about 50% wish they had something much lighter, nimble, and cheaper to fix when dropped.
The remainder are happy go lucky, good off road riders and/or masochists.

I mentioned earlier that the Honda CBF1000s (first gen) were known to fry stators. Honda's only change to the engine for the Gen 2 (2010-) models was to add a second oil passage to the alternator. So far I'm not aware of any stator failures on the Gen 2 CBFs, and I've been following the stator threads on the CBF forum. There's a few higher mileage riders with Gen 2's so it looks like Honda may have fixed their stator issues with increased oil volume.

I don't think there are any fins, but just ventilation .....
Here's an exploded view:

http://www.realoem.com/bmw/showparts.do?model=0B12&mospid=55258&btnr=12_1397&hg=12&fg=31

and here's a pretty good set of pictures: http://at.fotoalbum.eu/rubbermuh/a695272/

There is an oil outlet on the very bottom of the engine casting ...

Q1: How does oil ENTER the right side engine area?

Q2: What is the purpose of the big round "hole" at the top of the casting at about 11 o'clock here...
It just seems to be an open cavity in the side cover???
http://at.fotoalbum.eu/rubbermuh/a695272/00000004

Just looking at the flywheel, it is such a tight fit in the housing,
that I think the outside surface of the flywheel must be touching or slightly submerged in the oil at the bottom of the housing .. ...

I'm going to re-suggest a dumb idea I had about 35 pages back...
What if you drilled some holes thru the rim of the flywheel that were not quite "radially" drilled but had a slight leading angle and were countersunk on the outside surface of the flywheel ...

As the flywheel spins perhaps some oil would flow up thru the holes into the stator cavity offering some cooling as it got slung around?

On the original design the air surounding the stator was effectively trapped there - the only passage was the gap between the rotor and stator and then between the rotor and the outer case.There might have been some air movement due to hot air rising, but significent.

With the addition of the holes added to the new rotor there will now be turbulance which will cause air movement around the stator and within the entire cavity. This circulation will provide much more cooling because the heated air will be in contact with the entire casing instead of the small area next to the rotor.

This change was enough to convince me to replace the rotor as well as the stator. I expect it to be the last stator I replace thanks to the improved cooling.

Our new stator from RMStator.com arrived today.

Are there not supposed to be more epoxy dipping...... ???

I figure we'll have better cooling this way.

When you replace it with the BMW parts...is this all you ordered?

12 31 8 524 422 GENERATOR
11 11 7 704 757 FILLISTER-HEAD SCREW - 16X35
12 31 7 690 432 WASHER - A17
11 11 7 707 906 GASKET LEFT

I'm sure cooling is better un-dipped....

The downside is that, due to the AC-current flowing thru the wiring, there may be some induced vibration which could, over time, chafe thru the insulation of the wires ...

For $100 ... it looks ok...

I have an Electrosport unit on the way, I'll post a close-up of it when it gets here

This isn't the first time I've had a stator where the windings weren't encapsulated. I can't remember having problems with the others, to tell you the truth. As you say, for $100 it looks ok.