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Thread: 1994 K75S High-pitched chirping noise when hot?

  1. #1
    BMW uber alles! Zagando's Avatar
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    1994 K75S High-pitched chirping noise when hot?

    I'm getting an intermittent but fairly loud high-pitched chirping noise from somewhere under the tank when the bike gets hot.

    The radiator fan seems to be working OK and the chirping is independant of that; only thing in common is that it only occurs when the bike is running hot (now living here in Albuquerque that is much more often than my previous location where I first noticed it several months ago).

    I suspect a bearing somewhere; perhaps the water pump is acting up?

    If anyone can shed some light on what my problem might be that would be great. Hopefully it's nothing serious, but...

    Regards, Jeff
    ---Jeff

    ex: K75S Berlina R100GS/PD , K100RS , R75/5 , R60/2

  2. #2
    A bozo on the bus deilenberger's Avatar
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    Jeff - your best bet - visit a Harbor Freight and purchase a mechanic's stethoscope. That should let you localize it.

    "Under the tank" is a wide expanse of territory to guess where the noise is coming from. It could be anything from a bearing going bad somewhere, to the a plugged fuel filter (the fuel pump has a blow-off valve that chirps when it's pushing against too high a resistance.)

    Try to narrow it down a bit and get back to us with your findings.
    Don Eilenberger http://www.eilenberger.net
    Spring Lk Heights NJ NJ Shore BMW Riders New Sweden BMW Riders
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    Themason 42906's Avatar
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    Quote Originally Posted by Zagando View Post
    I'm getting an intermittent but fairly loud high-pitched chirping noise from somewhere under the tank when the bike gets hot.

    The radiator fan seems to be working OK and the chirping is independant of that; only thing in common is that it only occurs when the bike is running hot (now living here in Albuquerque that is much more often than my previous location where I first noticed it several months ago).

    I suspect a bearing somewhere; perhaps the water pump is acting up?

    If anyone can shed some light on what my problem might be that would be great. Hopefully it's nothing serious, but...

    Regards, Jeff
    Just so I am on the same page with you, does it ever chirp when the fan is not running?
    Experience is what you get when you don't get what you want.

  4. #4
    BMW uber alles! Zagando's Avatar
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    Yes, it chirps when the fan is on or off; doesn't make any difference.

    It always seems to happen when I am riding or at a stoplight and only when things are hot (ambient temps as well as the bike all warmed up in stop and go traffic.

    Maybe no need for a mechanic's stethoscope as I happen to have a medical stethoscope on hand (I was Dr. Mango Daiquiri come Halloween at my last job (bartender)). Perhaps it will come in handy again so I'll start carrying it with me when I go out on the bike.

    Thanks, guys!
    ---Jeff

    ex: K75S Berlina R100GS/PD , K100RS , R75/5 , R60/2

  5. #5
    Registered User kentuvman's Avatar
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    FWIW, my '87 K75s whined this past week when stopped at a traffic signal with the fan trying to keep her from overheating.

    Heck, I was whining too!

  6. #6
    BMW uber alles! Zagando's Avatar
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    Let's not confuse the whining of the fuel pump with this intermittant high-pitched chirp, please! Definitely out of the ordinary in my K-bike experience.
    ---Jeff

    ex: K75S Berlina R100GS/PD , K100RS , R75/5 , R60/2

  7. #7
    A bozo on the bus deilenberger's Avatar
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    Quote Originally Posted by Zagando View Post
    Let's not confuse the whining of the fuel pump with this intermittant high-pitched chirp, please! Definitely out of the ordinary in my K-bike experience.
    In case you misunderstood.. the fuel pump is capable of putting out 100PSI, until it burns up or explodes IF the output is plugged up (say by a bad fuel filter.) To prevent this from happening, it has a built in blow-off valve. That valve kicks in at about 80 PSI, and when it relieves the pressure, it sounds like a chirp. As the pump keeps running, it then sounds like a series of chirps. THAT is what I was referring to - not the normal whining noise (although that does get louder as restriction builds on the output of the fuel pump.)

    It's not a common noise - but it is a known noise. It may be out of the ordinary in your K-bike experience, but it is not out of the ordinary for everyone's k-bike experience.

    YMMV.. (but not a lot.)
    Don Eilenberger http://www.eilenberger.net
    Spring Lk Heights NJ NJ Shore BMW Riders New Sweden BMW Riders
    '07 R1200R (current ride) and some bimmers.. and a Porsche

  8. #8
    BMW uber alles! Zagando's Avatar
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    OK, Don, Thanks for that explanation. I was referring to Ken's post immediately preceding mine, though; not yours.

    There is the fuel pump whining which we're all accustomed to but this is an almost screeching, slightly warbly chirp. On and off, usually for as long as twenty seconds or as short as 2 or 3.

    From what you describe it very well could be that fuel pump pressure relief valve. It would certainly be worth my while to replace the fuel filter ASAP and see if it goes away. If not then I've at least eliminated one possible cause.

    With it occuring only when it's hot out that might make the most sense, too---I can often smell gas fumes when I'm sitting in traffic or at a light. The pressure must be all the more intense in these summer conditions.

    Thanks again and I'll let you know when I get a new filter in the tank.
    ---Jeff

    ex: K75S Berlina R100GS/PD , K100RS , R75/5 , R60/2

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    Don, where do you get this technical information? Wow! I am impressed (no sarcasm implied AT ALL) by the troubleshooting knowledge of some folks in this forum.

    Zagando, let us know if the stethoscope idea helped and the outcome. You should videotape the noise and post it for our own experience...ok, I am pushing it a little.

    I saw a stethoscope at Sears and almost went for it.
    1993 K75S Mystic Red Pearl
    2007 K1200GT 997 Blue

  10. #10
    Blocking the slow lane
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    Chirping? Does your bike still have the SHED emissions system installed?

    If you raise the back of the gas tank out of its rubber holders, there may be a hose on the right-rear side with gray-colored valve attached to it. You don't want that part there.
    Jon Diaz
    BMW K75/K12GT
    BMWMOA Ambassador

  11. #11
    Themason 42906's Avatar
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    Quote Originally Posted by deilenberger View Post
    In case you misunderstood.. the fuel pump is capable of putting out 100PSI, until it burns up or explodes IF the output is plugged up (say by a bad fuel filter.) To prevent this from happening, it has a built in blow-off valve. That valve kicks in at about 80 PSI, and when it relieves the pressure, it sounds like a chirp. As the pump keeps running, it then sounds like a series of chirps. THAT is what I was referring to - not the normal whining noise (although that does get louder as restriction builds on the output of the fuel pump.)

    It's not a common noise - but it is a known noise. It may be out of the ordinary in your K-bike experience, but it is not out of the ordinary for everyone's k-bike experience.

    YMMV.. (but not a lot.)
    That is very interesting information. Is that true of the later style K-1100/R-1100 fuel pumps?
    Experience is what you get when you don't get what you want.

  12. #12
    BMW uber alles! Zagando's Avatar
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    Quote Originally Posted by jdiaz View Post
    Chirping? Does your bike still have the SHED emissions system installed?

    If you raise the back of the gas tank out of its rubber holders, there may be a hose on the right-rear side with gray-colored valve attached to it. You don't want that part there.
    Don't think I have one of those at all; I probably would have noticed something like that in all of the times I've taken off the tank for one reason or another---but thanks for the the thought, nonetheless.

    I'll get over to a local Napa outlet later and get a new fuel filter later today. I just discovered that it's been almost three years since I changed the FF so it can't hurt even if it's not at the root of the problem.

    Regards, Jeff
    ---Jeff

    ex: K75S Berlina R100GS/PD , K100RS , R75/5 , R60/2

  13. #13
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    Quote Originally Posted by Zagando View Post
    Don't think I have one of those at all; I probably would have noticed something like that in all of the times I've taken off the tank for one reason or another---but thanks for the the thought, nonetheless.
    Do you have ANY hoses attached to the two vent ports at the right rear of the tank? Or do you have the "cup" (air accumulator) attached to the frame directly underneath these two vent ports with no hoses connected to the right rear of the tank?




    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

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

  14. #14
    BMW uber alles! Zagando's Avatar
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    Only the little cup, Lee---no hoses.
    ---Jeff

    ex: K75S Berlina R100GS/PD , K100RS , R75/5 , R60/2

  15. #15
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    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

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

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