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Thread: 1994 K75S Timing Chain Rattle

  1. #1
    Slipster Slipster's Avatar
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    1994 K75S Timing Chain Rattle

    I own a 1994 K75S. 56,000 miles on a well maintained brick. I have a typical timing chain rattle at low rpms that does go away at higher revs. Smooth engine performance over all of the rpm range.

    I would expect the chain to be ok. I suspect the Chain Tensioner, Tension Strap, Slide Rail and Guide Rail to be the cause of the rattle.

    Is this something that I can do? I am not sure of how to remove the chain and preserve it's position in regards to timing preservation to then get to all of the parts that I need to replace.

    Hoping to get rid of this really annoying chain rattle
    Expect The Unexpected

  2. #2
    Benchwrenching PGlaves's Avatar
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    I suspect that what you are heating is gear backlash between the gear on the crankshaft and the gear on the output shaft. I heard a noise at 60K which I believed to be chain noise. I bought a new chain and tensioner rubbing block. I took the engine apart. I measured the extended and compressed length of 20 or whatever links per the manual and compared it to the new chain. They were the same.

    I put the old chain back in. I didn't change any tensioner parts. I continued to ride the bike and continued to hear the same noise but it never got worse.

    That chain and tensioner were still the same parts that came out of the factory when the bike was new 310,000 miles later when the bike died in an accident at 370,000 miles.

    The chain is in a clean environment, well lubricated with oil. They seem to be very robust. I would be surprised if either the chain or tensioner needed anything at such low mileage.
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
    http://www.bigbend.net/users/glaves

  3. #3
    Rally Rat
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    I agree with Paul, as usual. I've heard the same complaint since the K75s were new bikes.

  4. #4
    Slipster Slipster's Avatar
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    Thank you my fellow Beemer Brothers. I appreciate your guidance as it saves me a lot of work and frustration
    Expect The Unexpected

  5. #5
    Registered User argent brick's Avatar
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    Quote Originally Posted by PGlaves View Post
    I suspect that what you are heating is gear backlash between the gear on the crankshaft and the gear on the output shaft.
    When do you hear said noise? My K75 has 51K on it and I hear a noise like this too.
    I assumed it was timing chain also. Anything else it could be?
    Lynn
    MOA #57883
    Current Ride: 1995 K75 Standard
    Past: 1978 Yamaha XS 750, 1976 BMW R60/6

  6. #6
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    Is this the infamous K-rattle that happens around 2300 RPM and then disappears? Just K75s?

  7. #7
    Slipster Slipster's Avatar
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    yes right around 2,000. At idle it can happen but pulling in the clutch and letting it back out will make it better. Worst rattle is when I am in 1st gear and let the clutch out while giving it some gas - it is at that time that the rattle is the loudest and then goes away once the rpms go up. Any gear will produce that sound if the engine lugs down into that rpm range. I can live with it but it is annoying only because it is such a smooth performing and sounding bike.
    Expect The Unexpected

  8. #8
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    I have read on other forums and blogs that this noise is common to all K75s and is normal. It sounds as if we are confirming that.

  9. #9
    Registered User argent brick's Avatar
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    I have noticed it when I am rolling on the throttle. I this what you guys are talking about?
    I am new to K bikes.
    Lynn
    MOA #57883
    Current Ride: 1995 K75 Standard
    Past: 1978 Yamaha XS 750, 1976 BMW R60/6

  10. #10
    Slipster Slipster's Avatar
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    Looks like there is a shim at the rear end of the motor's output shaft that could be the culprit. Way too deep of a surgery for me to do just to take up some slack in the anti backlash gear

    Expect The Unexpected

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