F800ST stator/voltage regulator replacement and oil - BMW F800 Riders Forum & Registry



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  1. #1
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    I know its probably been done to death on the forum, but I couldn't find the answers with a search and I'd appreciate a couple answers;

    I'm in the process of changing a burnt stator (voltage regulator while I'm at it) on my 2008 F800ST. A decent amount of oil came out of the engine stator cover, which I assume is normal?

    Am I correct in saying the oil inside the stator assembly is normal engine oil? I just had a car mechanic tell me it was gearbox oil which doesn't seem right.

    Thanks for any input

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  3. #2
    Bogbody's Avatar
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    Engine oil. Gearbox shares the same oil - common on most bikes.
    F800GT in blue known as "The Blue Bat"
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    Engine oil. Lubricates and helps cool the engine, clutch, stator, gears.....

    There are only four fluids - brake fluid, coolant, suspension fluid and engine oil. And gas.

    The mechanic may want to stick to diagnosing things with four wheels. Or not offer unfounded advice.
    Concrete remains undefeated. 

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  6. #4
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    It's the reason we have the alternator. The alternator is the part that creates that power. As you're driving along, the alternator makes energy to control the framework while the overabundance energy is utilized to re-energize the battery.

  7. #5
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    Welcome, Jacquelartin. Why don't you fill out your profile and let us know what motorcycle you ride and where you live. That would help us answer any questions you may have.
    Richard - Current bikes: 2016 BMW R1200RS, 2018 16.6 kWh Zero S, 2011 Royal Enfield Bullet 500 Classic, 2009 BMW F650GS, 2020 KTM 390 Duke, 2002 Yamaha FZ1 (FZS1000N) and a 1978 Honda Kick 'N Go Senior. 

  8. #6
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    I thought blinker fluid comes out when the stator cover is removed!

    'cause, you know, the stator drives the blinkers, right?


    But seriously, it is easier to make stator windings run in motor oil than it is to seal a chamber to keep oil and water out. Plus the motor oil can help keep the stator from getting extremely hot in a sealed compartment. Motor oil is hot but not as hot as wires can get.
    2016 Yamaha FJR1300A; 2016 Beta 430RS; 2007 BMW F800S; 2009 Husaberg FE450; 2016 Subaru Outback; 2018 F150; 2013 Tesla Model S 85; 1983 Porsche 928S; 9 cats 

  9. #7
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    As mentioned above, the oil is there to cool the stator. There were lots of early model stator failures due to the rotor design that didn't let much oil through. The newer design (2010ish) looks more like Swiss cheese which aids in cooling and prolongs stator life. I replaced my stator 4 times on my 08' ST before finally upgrading to the new rotor. It's been great since then.

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    Quote Originally Posted by ccramerusc View Post
    As mentioned above, the oil is there to cool the stator. There were lots of early model stator failures due to the rotor design that didn't let much oil through. The newer design (2010ish) looks more like Swiss cheese which aids in cooling and prolongs stator life. I replaced my stator 4 times on my 08' ST before finally upgrading to the new rotor. It's been great since then.

    Sent from my SAMSUNG-SM-G891A using Tapatalk
    More like 2013ish.

    Sent from my SM-T813 using Tapatalk

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    Quote Originally Posted by ccramerusc View Post
    As mentioned above, the oil is there to cool the stator. There were lots of early model stator failures due to the rotor design that didn't let much oil through. The newer design (2010ish) looks more like Swiss cheese which aids in cooling and prolongs stator life. I replaced my stator 4 times on my 08' ST before finally upgrading to the new rotor. It's been great since then.

    Sent from my SAMSUNG-SM-G891A using Tapatalk
    I'm pretty sure my stator is burnt out as well. I tested the reg/rec and it seems fine, haven't tested the stator yet (that plug is a PITA to get to), but voltages at idle are between 11.7-12.3, with occasional spikes to 13.3V while riding. Voltage does not go up uniformly when I increase throttle, but the spikes seem to suggest the stator is working SOME of the time (but usually not).

    I'm about to order a new stator from electrosport once I confirm the stator is dead, but how much of a pain was it to upgrade the rotor?

  12. #10
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    Quote Originally Posted by rodzghost View Post
    I'm pretty sure my stator is burnt out as well. I tested the reg/rec and it seems fine, haven't tested the stator yet (that plug is a PITA to get to), but voltages at idle are between 11.7-12.3, with occasional spikes to 13.3V while riding. Voltage does not go up uniformly when I increase throttle, but the spikes seem to suggest the stator is working SOME of the time (but usually not).

    I'm about to order a new stator from electrosport once I confirm the stator is dead, but how much of a pain was it to upgrade the rotor?
    You have proven the problem is not the battery? A perfect stator can't punch a battery with dead cell much over 13.2V.
    2016 Yamaha FJR1300A; 2016 Beta 430RS; 2007 BMW F800S; 2009 Husaberg FE450; 2016 Subaru Outback; 2018 F150; 2013 Tesla Model S 85; 1983 Porsche 928S; 9 cats 

  13. #11
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    It's a bit of a pain, but I have found that heat and a good impact wrench make it manageable. The rotor is heavy so it takes a while to get it up to 350 degrees f. You'll need a powerful torch (not a flashlight!). Once it's hot, hit it with an impact wrench. Don't try to lock the engine in TDC and use a big cheater bar like the shop manual says. The impact wrench is much more effective. Be prepared to catch a very hot rotor when it breaks free. Oh yeah, you will need a puller like this: https://smile.amazon.com/dp/B002308E...ing=UTF8&psc=1

    The biggest challenge is finding a new one to install. BMW only sells them as a kit with a stator. You will need special thread locker for the installation.

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  14. #12
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    Quote Originally Posted by N4HHE View Post

    You have proven the problem is not the battery? A perfect stator can't punch a battery with dead cell much over 13.2V.
    After reading all these posts about looking at reg/rec and stator first, I was a bit wary about just popping in a new battery and testing that. But I suppose that battery could be a good second step now that I've confirmed the reg/rec is at least preventing the battery from being over-charged. It also looks like the diodes are all functioning properly, as my meter shows that current can only flow one way.

    Now that I think about it, my new battery was able to get up to 14.5v on my battery tender, but the old one never goes past 13.3v, so it could very well be what you say about a dead cell.

  15. #13
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    Quote Originally Posted by rodzghost View Post
    Now that I think about it, my new battery was able to get up to 14.5v on my battery tender, but the old one never goes past 13.3v, so it could very well be what you say about a dead cell.
    Put the questionable battery on a maintainer or proper charger and see what its doing the next morning. 13.3 is right in that magic range which shouts, "Dead Cell!"
    2016 Yamaha FJR1300A; 2016 Beta 430RS; 2007 BMW F800S; 2009 Husaberg FE450; 2016 Subaru Outback; 2018 F150; 2013 Tesla Model S 85; 1983 Porsche 928S; 9 cats 

  16. #14
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    Update: turned out I had a burnt out stator. New one is in and I get a steady 14.3—14.4 V, even at idle. Hardest part was getting out the screws I stripped that were holding in the metal tab for the wires. Note to self: get a pozi drive bit for the next time.

    Reg/rec tested fine, but might upgrade that to a mosfet one. One thing that did concern me a little is that the epoxy was broken in a few places on my new electrosport stator. Seems to be running fine as is, but I might go back in and seal those spots up.

    Lastly, once I had the old battery off, the tender was able to get it to 14.5v before dropping down into trickle mode. Pretty sure it's still toast though from all the times I saw it dip down below 10 v while running.

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