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Thread: dead K75C

  1. #1

    dead K75C

    I finally sold my long term K75C project to a friend who bought it for his son for Christmas as his first motorcycle. All he needed to do was ride it across town which is ten minutes away and park it in his garage. I thought to myself, I never thought I'd see the day but it was going to a good home.

    That's when all the trouble started. Just short of his house the bike died. He started it up again and it went a little further and died again. this time it would not restart. He pushed the bike a couple of blocks and into his garage where he called me to tell the story. This is where it gets weird. There are dash lights but no parking light or headlight. The emergency flashers work but if you turn on either turn signal you get the emergency flashers again. You can hear the fuel pump whirr and there's a click from the starter relay but the bike will not turn over. The battery is in excellent condition. I even tried a battery from another bike.

    I recently had the front top end of the bike apart to check if the handlebars were bent prior to selling. I started there because I wanted to be sure there was not a pinched wire or cable due to my assembly. If it were just that the bike wouldn't start I'd focus on the starter circuit but all the other electrical gremlins have me completely baffled. I'm focused on finding the obvious broken or loose wire but that hasn't happened yet. I know it's a simple fix but it's a bit frustrating at the moment.

    The funny thing is I bought the bike for next to nothing but have poured more money into it than I should have. The bike has never had any electrical issues until now.

    Please lend me your expertise. All opinions are welcome.

  2. #2
    3 Red Bricks
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    John,

    The symptoms you described sound like you have a dirty starter commutator. The load shed relay grounds through the starter, so that wuld give you the wierd light problems. What happens is the carbon dust from the starter brushes builds up inside the starter on the commutator so they don't make good contact.

    The starter needs to be removed, disassembled, and cleaned. Be sure to mark the rotational relationship of the end bells to the center section of the starter and which one goes on which end. Use BraKlean and Scotchbrite to clean the commutator.

    But, before you go to all that work, get your volt meter out and insure you are getting 12 volts to the starter terminal when you push the start button (key on, kill switch in run position). If you do, the starter needs cleaning.



    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

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

  3. #3
    Lee

    Thanks for you quick response. To be sure I am testing the starter correctly, I have the red lead of my ohmmeter on the starter terminal and the black lead grounded to the engine case. Key on, kill switch in the run position, push the starter button and all I get is a clicking starter relay. No voltage shown on the meter.

    Does it sound like I did that correctly?

    John

  4. #4
    3 Red Bricks
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    That should work, but normally when trying to troubleshoot things on these bikes, it's best to use the bolt on the transmission,just above the shift lever where the battery ground cable connects to the bike for your ground. What is the voltage between this point and the battery positive post at rest? What is it while trying to crank the bike?





    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

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

  5. #5
    I may have gotten ahead of you.

    What I had done before your latest reply was to put voltage directly to the starter terminal. Nothing happened with the starter but the headlight would come on each time I touched the lead to the starter terminal. I pulled the starter out and without taking it apart I applied voltage by just touching the terminal intermittently to see if the starter would turn over. No such luck.

  6. #6
    3 Red Bricks
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    And I assume that you also grounded the starter housing to the battery. If so, you need to disassemble the starter and clean the commutator.




    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

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

  7. #7
    Lee

    Thank you so much for your insite. I took the starter apart and was it ever filthy. The commutator was pretty dirty and one of the brushes looked to have been arcing. I cleaned everything up, put it back together and bench tested it. Spun like a champ. I installed it in the bike, turned on the key, all the lights worked again and when I pushed the start button the engine cranked right over. I only cranked the motor for a few revolutions since I have the gas tank off. I would venture to say that that was the entire problem and I can put the bike back together.

    My only concern was the brushes and seals for the starter and that maybe I should replace those or put a new starter in for the kid.

    Thanks again

    John

  8. #8
    3 Red Bricks
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    If you have less than 150,000 mi on it, it SHOULD be fine (unless it was a whole bunch of 5 mile rides). If there was no travel left in the brushes when it was on the commutator, you might need new brushes.

    12 41 1 459 567 SET: CARBON BRUSH SET $18.75 (one brush)

    12 41 1 459 297 BRUSH HOLDER PLATE $16.46 (the other brush and holder plate)



    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

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

  9. #9
    The bike has about 58,000 miles on it but I'm sure it was ridden hard and put away wet a lot before I found it. The brushes had travel left and were approximately 3/8" long. I understand that when they reach 1/4" long they are just about done. I never did remove the alternator during the restoration. Any thoughts about doing that as long as the idiot light goes out and I can measure almost 14V at the battery?

  10. #10
    3 Red Bricks
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    Both should be fine. My alternator brushes lasted till 115,00 miles and my starter has 145,000 on it but has been cleaned twice.



    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

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

  11. #11
    Lee

    Thanks for all the help. You are a wealth of knowledge. I have to admit I was pretty frustrated by the end of this week have to face a step by step elimination of each circuit. When I got home last night I thought why don't I post a message on the forum. For it being my first time i have to say i am totally impressed. It's nice to know there are "flying brick" experts out there happy to lend a hand. Thank you again and Happy New Year to you and your family.

    Sincerely

    John


  12. #12
    Curmudgeon At Large Bobmws's Avatar
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    While the tank is off, clean the clump of ground wires that bolt on to the frame back bone.
    Bob Weis
    Bikeless! 2004-bmw-k12rs-hannigan-Sold!

  13. #13
    got it, thanks....

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