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Thread: '85 K100RS, Signs of a Failing Water Pump.

  1. #1
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    '85 K100RS, Signs of a Failing Water Pump.

    I'm looking for information regarding how a water pump on a K gives signs that it's failing. The cooling fan is funtioning normally and comes on when hot without any howling or anthing, however when hot I'm getting other sounds like the coolant boiling or bubbling. Also following my return yesterday from the Stanley Stomp, I noticed a light metallic sound coming from the vicinity of the water pump, while the engine idles. Any help or ideas would be appreciated. Thanks for your response in advance.
    gp
    Gary Phillips - #6322
    Wildland Firefighter, Retired, Riggins, ID
    Heartland Moto Locos BMW Riders
    '77 R100/7 Dirt Hack, '83 R80ST, '85 K100RS w/EML, '00 R1100RS

  2. #2
    3 Red Bricks
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    Gary, the normal failure of the water pump is a seal failure which would show up as a coolant leak from the weep hole at the front of the oil pan.

    Are you sure the coolant is full AT THE RADIATOR CAP under the front of the fuel tank?

    The light metalic sound could be coming from worn guides on the timing chain.

    I don't know if it's possible for the impeller to come loose from the pump shaft.





    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

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

  3. #3
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    Copy on the coolant fill. I checked it at the radiator cap, thinking there may be a bubble in the system. I let it run with the cap off until it came up to temp with no appreciable change in level. Did timing chain and guides last spring, about 8,000 miles ago. Still scratching my head over this but it seems to be heat and cooling system related. Thanks for your response.
    Gary Phillips - #6322
    Wildland Firefighter, Retired, Riggins, ID
    Heartland Moto Locos BMW Riders
    '77 R100/7 Dirt Hack, '83 R80ST, '85 K100RS w/EML, '00 R1100RS

  4. #4
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    Found the source of the metallic sound, I've had the exhaust system off recently and following the trip to Grandjean, the site of the Stanley Stomp, which included six miles in and six miles out of dirt road, one of the headers had loosened slightly. Retorqued and metallic sound gone. Still think I have a cooling issue. No leaks or drips from the water pump housing. I'll try semi removing the fuel tank and running the engine with the radiator cap off to allow any existing air bubble to escape.
    Gary Phillips - #6322
    Wildland Firefighter, Retired, Riggins, ID
    Heartland Moto Locos BMW Riders
    '77 R100/7 Dirt Hack, '83 R80ST, '85 K100RS w/EML, '00 R1100RS

  5. #5
    Thanks for the follow-up.
    I'd never heard of a coolant pump failure via metallic noise or whine. As mentioned, they are typically a seal failure spotted by leakage through the weep hole.

  6. #6
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    10 miles from home on a one week trip to Maine one Saturday morning in 2011 my 85 K100RS w 134,000 mi. overheated and lost water and had oil in water, a gray scum in the black coolant bottle near the battery. Added water, rode home by 8am. Studied the web, took pump off and apart. Drove my car 90 min to a great dealer in Baltimore to get the rebuild parts by noon to rebuild the pump. Earlier that summer it had overheated near the Bloomsburg PA Nat'l Rally.

    By the way, the parts were an upgrade kit. Early K bikes had a shaft with a step near the end with a nut to hold the impeller tight on it. The shaft would fatigue at the step and crack and loosen the seals and impeller. The upgrade kit uses a hole in the shaft for a bolt that holds the impeller on with a much longer fatigue life. I think I have that right, not the other way around.

    Home by 1:30, by 5 pm I had the rebuild parts on and cleaned the coolant system and took a successful test ride to my adult son's baseball game, 15 miles twice. The next morning I left for Maine and had a good trip, things have been fine for something like 60,000 miles since.

    Mine did have the overheat light come on this summer in 95 deg air, two up camping, 65 mph two lane road, up a gradual pass at 6-8,000 feet heading north west toward Vernal UT.

    Hope this helps.

    177inthe70s
    85K100RS w 195,000 mi from Phila.

  7. #7
    FWIW, every water/oil pump I had to rebuild was from 80s or early 90s vintage K bikes. Later 90s K1100s and the K12s have never weeped on me.
    I also seem to recall that BMW discontinued the rebuild kit for the pump. Last time I went looking they wanted to sell a whole new pump.

  8. #8
    3 Red Bricks
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    Parts are still available individually to rebuild the pumps.

    Pre-1990 pumps must be upgraded to post-1990 impeller.



    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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