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Old 12-27-2011, 01:26 AM   #165
Gnarly Adventurer
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Joined: Sep 2011
Location: Austria
Oddometer: 471
Originally Posted by vtbob View Post
It is clear that stator windings are being chared and failing. Fact one. The question is why and what the root cause is.

Failures seem to come at 30,000 miles or more. Certainly not evenly distributed over the same rate of failures on new bikes and on the higher milage ones. Is this an important clue? Could this age related condition be fact two?

A first though logically it that it is too hot. Why?
Has the engine temp in the stator housing gone up over time? If so what would cause that?
A lot of talk about exhaust pipe temp contributing. Are exhaust temps hotter on older bikes. Are the exhaust headers closer or touching the case? Not enough info on this but the ad hoc info seems there is no change here.
Is there any real info to support the idea the stator housing gets hotter with the age of the bike? No?
So if the stator housing is not hotter with age, what would cause the stator it self to get hotter with age?
Is there more current flowing in "old" stators than new? If so what would cause this excess current?
Are the magnets on the rotor getting stronger with age? Are they rotating closer to the stator...higher flux density so more current is made? An area to think more about.
Could the regulator malfunction increase the currents in the stator? Most say no because of the design. Is that really true in all failure mods?
Does the copper winding in the stator age? Would this aging cause over heating? No?
Does the insulation on the stator winding age? Would this aging cause shorted windings and over heating? Would these shorts cause gradual output voltage reductions...that could be measured as a precursor symptom?
Why would the stator insulation age / fail? Poor material used? Some type of contaminations? Vibration cause cracking? All good things to think about and get more info.
Has anyone really analyzed a failed stator?
I really like your approach to the problem, where most questions are the same I asked myself.

Checked a German forum and they only had two similar incidents. Not many considering the high number of F8's sold there.
What me concerns most is the fact that basically everything works fine and the problem occurs only after a certain mileage. Well, some exceptions seem to prove the rule.
So if heat is the problem why doesn't it kill the alternator immediately? Cowboys approach with the heat resistant tape sounds good but I doubt that the exhaust tubes really roast the alternator. I checked with my F8 and the tubes are in my opinion not a problem, at least not when riding, but the may be when going really slow and there's no air flow.
Like cowboy I can build up a plane (mechanically) but I am clueless about the electric stuff so I can't say anything to the different types of rectifiers and related stuff.

BMW sure knows whats going on and it pisses me no end that they don't state the reason. Knowing the reason would help to find a way to solve the problem....
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