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Thread: 1987 K75C 57k Karibic Bleu Charging troubleshoot question

  1. #1
    PeteG
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    Dec 2009
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    1987 K75C 57k Karibic Bleu Charging troubleshoot question

    Symptom(s) and current remedy

    Very low battery charge causing stuck starter relay making three delayed attempts to turn engine when off before battery quickly died.

    Replaced relay, inspection of original relay showed no fusing of contacts. It will be my spare.

    Replaced 10 year old battery with new. Ran great for 30 mile back country commute home and got a bright battery warning light upon commute-end idle. Increasing RPM would dim light. Started right up the next morning and made return 30 mile trip to shop. Again, got bright warning light upon commute-end idle. With engine off new battery had 12.58 v charge.

    Started engine and checked battery voltage at 3000 RPM and it did not move. Tested battery voltage on my other K75C at 12.6 v at rest, and jumped to 13.6 v at 2500 RPM.

    It seemed pretty clear the battery was not getting a charge. Removed alternator. Bearing felt good, contacts need cleaning, brush protruding lengths; 1 at 5mm and 1 at 6 mm. (5 mm is the service limit) Brush springs were not binding.

    I might have to call around to see if anyone can bench test the alternator. Is it likely that just the brushes need replacing if I can’t find anyone local to do the bench test? I have no knowledge of whether the symptoms could indicate a bad rectifier. I already asked one local motorcycle repair veteran for a bench test reference without luck.

    Euro Motoclectrics sells a 33 Amp remanufactured Alternator for $179. The entire voltage regulator is $39. I can afford the purchase. I have no need for the 50 Amps on either of my K’s. If I wanted to solder, the brushes are available for $19.50.

    Thanks in advance for your suggestions,
    Pete

  2. #2
    PeteG
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    Dec 2009
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    Woodacre, California
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    Smile

    UPDATE

    1987 K75C Karibic Bleu: (I had the year wrong in my original title line)
    I replaced the at service limit 5mm brush and voltage regulator assembly. Upon assembly and voltage testing at 3000 rpm indicated no charge going to battery.

    The alternator from my 2nd 1988 White K75C with 205K mi. was “borrowed” for install on the Karibic Bleu. Prior to install I checked the brush length, and here is where I learned what I did not know. The 5mm service limit brush length does not mean an alternator stops charging effectively at the 5mm length, as the brush length on White K75C alternator was down to 3mm. Voltage test at 3000 rpm on the White K75C was 13.8 v with short brush length. The new voltage regulator and brush assembly was installed onto this known good alternator and reinserted into K75C Karibic Bleu.

    3000 rpm voltage test at battery indicated 14.01 v. Bleu is running like a champ as I also had discovered and replaced a split crankcase breather hose.

    Refurbished alternator was purchased from Euro MotoElectrics and am awaiting delivery to replace non-charging alternator.

    I’m having an intermittent stumble-at-idle problem on the White K75C and will address on a later thread. I’m chasing several theories. Battery issue or temp sensor are current suspects.

    Ride Safe,
    Pete

  3. #3
    Liaison 20774's Avatar
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    Thanks for the update! I'll change the title for future searches.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  4. #4
    3 Red Bricks
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    Quote Originally Posted by pjar View Post
    UPDATE

    I’m having an intermittent stumble-at-idle problem on the White K75C and will address on a later thread. I’m chasing several theories. Battery issue or temp sensor are current suspects.

    Ride Safe,
    Pete
    Pete,

    How many miles ago was your last valve adjustment and throttle body adjustment?

    Plugs still in good shape and proper gap?






    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

    Lee Fulton Forum Moderator
    3 Marakesh Red K75Ss
    Mine, Hers, Spare

  5. #5
    PeteG
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    Quote Originally Posted by 98lee View Post
    Pete,

    How many miles ago was your last valve adjustment and throttle body adjustment?

    Plugs still in good shape and proper gap?






    Hi Lee,
    Thanks for reaching out with the suggestion of tackling the easiest task first. I need to do a throttle body adjustment. I have a Twinmax but have not yet used it. That will be my next step once it gets running.

    I did a valve adjust and plug replacement a few hundred miles ago. Unbelievably the old plugs looked great other than worn and too large gap. Only one valve was out of spec and needed a different shim size. I triple re-seat and re-check gap after shim replacement so I'm thinking this isn't the problem. Performance was noticeably improved after new plugs and gap adjust. I do know my battery needs replacement since standing voltage begins at 12.6 v and after 90 seconds with the lights on (not running) drops to 11.7 v. Battery also charges unusually fast. So battery replacement and waiting for refurbished alternator is step one. The battery is a cheap 12 month warranty on its 3rd year.

    The thought just occurred to me that I should share my "valve shim PDF template" file. It is a visual and data record of all known installed shims and lets the user (me) know what the next needed shim size will be. I can make it a fillable PDF so the user can enter data as needed either on the computer or in writing as a print-out. That will be on my "to-do" list.

    I'd love to have a way to test plug wires. I cannot fathom how they are still performing after 30 years.

    Take care,
    Pete

  6. #6
    Registered User barryg's Avatar
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    Most BMW K75 owners will tell you their Red K75's will charge faster than your blue K75. Just a little heads up.

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