Another alternator hits the dust and not under warranty

[Emmbeedee]

Originally Posted by Reaver

With the bike running the oil level would be next to nothing. Remember also that the stator is surrounded by the rotor, which rotates? So any oil would be flung centrifugally (today's word) all over the hot stator, which just screams as anyone would in that situation.

Oil does not get flung on the stator which is inside the rotor. It's simply not possible. It gets flung away from it.

[Moto Mikey]

I ordered a Rick's Stator this morning.

Where's the best/cheapest place to order the Compufire R/R?

[Reaver]

Originally Posted by Emmbeedee

Oil does not get flung on the stator which is inside the rotor. It's simply not possible. It gets flung away from it.

I thought we all agreed that the stator was oil cooled? Oil is being flung onto it.

Anyways, you're missing the point. JrWoody was thinking there was a "high water mark" on the lower part of the stator so to speak. I'm sayin that when the engine is running, the oil would be evacuated from inside the rotor cavity. Since the stator aint moving, any oil on it would drip down from gravity. This all would nullify any oil level effect.

Besides, I like picking on JrWoody ( JrWooden) .

[Gaspare]

@ Mikey: Amazon, I think, even if it's rised now... let's search 55402

[JRWooden]

Reaver Reaver Reaver ....

I don't think you're drinking enough...........

Ok seriously ....
at some point in the bike's "life" ...
some amount of oil must be getting in there unless the deposits we are seeing on the stator are not oil-related ... or unless they are caused by just some oil "mist" or some such crap ... I don't know
For the sake of argument let's say that when the bike is canted over in a hard right turn that the oil level come up above the "top" of the inside lip (counterbore) of the flywheel.... what happens?

Adding resistance in the 3 wires coming from the stator - Joel was using small amount of resistance 0.1 - 0.2 ohm as I recall...

This reduces current through the stator instead of letting the R/R "short-circuit" it to ground and limit current only as result of other limitations .... heat in the stator being proportional to I^2 ... (eye-squared) seems this would help ... at least to me ... basically it turns the 400W stator into a ~320W stator based on some rough calculations I did.......

Sure wish the new design had come out while my bike was still under warranty............

PS: Indy is sending me a flywheel... guess who's gonna find out

[Emmbeedee]

Originally Posted by Reaver

I thought we all agreed that the stator was oil cooled? Oil is being flung onto it.

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.

[guzzimike]

Originally Posted by Emmbeedee

Oil does not get flung on the stator which is inside the rotor. It's simply not possible. It gets flung away from it.

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

[JRWooden]

Originally Posted by Emmbeedee

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.

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 .......

[WayneC1]

[QUOTE=Unless BMW defied the laws of physics. [/QUOTE]

BMW tried ....and failed.....The stators overheat

[Emmbeedee]

Originally Posted by guzzimike

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

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

[Emmbeedee]

Originally Posted by JRWooden

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 .......

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.

[JRWooden]

Originally Posted by Emmbeedee

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

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..............

[vtbob]

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.

[vtbob]

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?

[Reaver]

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?