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Thread: oil puddle behind intake valve/compression issue '85 K100RS

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  1. #1
    WrenchMeister jeffeaby's Avatar
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    oil puddle behind intake valve/compression issue '85 K100RS

    K100RS 85...removed the throttle body assembly for trouble shooting a hard to start bike. looked down into the head cavity where you can see the back side of the intake valve. Small puddle of oil sitting in there...about a spitwad's worth. Can I assume my valve seal is leaking and/or is this normal. The other three are dry. About 70K miles...just did a head gasket change and it seemed to be running well...until the hard to start syndrome hit. My local mechanic told me not to bother with seals and valves while the head was off...did I make a mistake by not dealing with them at the time.

    Also, three of the four cylinders have compression at 165 psi, but one has 135 psi (different cylinder than the oil problem). changed a marginal valve shim and haven't check for change yet, but can a marginal shim (was too tight) be the cause of inferior compression? Do I have ring problems in that cylinder?

  2. #2
    Rally Rat
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    In what condition are the rubber boots between throttle body and plenum chamber? If one is leaking, oil mist from the breather will trickle down the throttle body.

  3. #3
    WrenchMeister jeffeaby's Avatar
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    oil was in cyl #1...others dry. ALL rubber replaced with new (quite the investment!) during the head gasket change.

  4. #4
    A bozo on the bus deilenberger's Avatar
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    jeffeaby,

    Welcome to the forums. Please read: http://www.bmwmoa.org/forum/showthread.php?t=46057 - I've added that info to your thread title, please do so yourself in future posts to the tech forums.

    As to your problem.. I wouldn't immediately guess the valve guide seals, although with a 27+ year old bike, most anything rubber is suspect. I would wonder about the condition of the rings and valves in the cylinder with the low compression.

    You mentioned you haven't done another compression test since the valve adjustment. That's certainly in order - and make certain you do it with the throttle locked fully open (otherwise you can get odd readings). If the cylinder is still low I think a leakdown test might be in order. It's possible to burn a valve if a cylinder runs too lean, and that could happen if you had bad intake rubber mounts. If you have bad rings - then blowby past the rings can cause excessive flow through the crankcase breather, which could push some oil up into the intake plenum, and depending on how the bike was situated - it would tend to flow to the lowest point, which might be cylinder #1.

    Can we assume it now starts OK?

    I think we'd just be guessing until we have more info, so the compression test redo is pretty vital, and if it's still off - the leakdown test should reveal where the compression is being lost.
    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

  5. #5
    WrenchMeister jeffeaby's Avatar
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    did another compression test following the valve shim change...all cylinders are up to snuf. surprized they are all so good at 70kmiles, but there they are.

    Still can't get the bike to start. have checked all the FI components, they are all seemingly within spec. every time I pull a plug to inspect, it's soaked. Have tried every combination of mixture settings on the airflow meter bypass and throttle idle adjust screws. have pulled all plugs and see spark in the gaps.

    Need some advice on getting the mixture set right. I can put an oscilloscope on the injector signal...what's the pulse look like on a goos system?

  6. #6
    3 Red Bricks
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    Are you SURE that the boot between the air filter box and the intake plenum is properly seated all the way around?

    Are you sure that the cams were properly timed when you replaced the head?



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  7. #7
    Rally Rat
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    Quote Originally Posted by jeffeaby View Post
    did another compression test following the valve shim change...all cylinders are up to snuf. surprized they are all so good at 70kmiles, but there they are.

    Still can't get the bike to start. have checked all the FI components, they are all seemingly within spec. every time I pull a plug to inspect, it's soaked. Have tried every combination of mixture settings on the airflow meter bypass and throttle idle adjust screws. have pulled all plugs and see spark in the gaps.

    Need some advice on getting the mixture set right. I can put an oscilloscope on the injector signal...what's the pulse look like on a goos system?
    I've never 'scoped them, but they should be switched open for 3-5 milliseconds for starting.

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