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Thread: Piston ring rotation

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  1. #1
    Atomic City Boxer 154048's Avatar
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    Nov 2009
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    Piston ring rotation

    Greetings,
    Here is an interesting hypothetical...My 1980 R100 began to smoke quite a bit from the right cylinder with relatively sudden onset. (Mileage 65K)
    I pulled the head and cylinder expecting to find a broken ring. All rings fine, but I did notice that the bottom (oil) ring' opening was straight down at 6PM position.
    The next ring was at approximately 5:20. The top compression ring was around 10:00.

    I have heard that rings tend to rotate around the piston after a fashion...might they have rotated so that the two lower rings were both open in the same area? If so, would this cause oil to blow past them and overwhelm the top ring, hence the oil burning?? The spark plug on that side is a nice tan color, so the oil burning hasn't been going for long.
    What are your thoughts??

    Thanks

    PS... I may re ring it anyway, but may not if it was a 'ring rotation' issue. everything else is in very fine appearance...valves, piston skirt, cylinder walls ...meaning no recession, scoring etc
    Steve in Santa Fe
    1980 R100RT
    2005 DR 650

  2. #2
    Cave Creek AZ 85K100LT's Avatar
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    Jan 2006
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    Angry Ring rotation - not the problem

    Ok so you started burming oil on the right side. How do the valves look?? Sounds like a valve guide problem.
    1974 R75/6 W Sidecar
    1989 R100GS


  3. #3
    Atomic City Boxer 154048's Avatar
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    I don't notice any visible 'issues' with the valves. Exhaust valve not sinking etc...
    My confusion comes because it seems like the right cylinder began smoking quite suddenly...no problems with left cylinder...
    Steve in Santa Fe
    1980 R100RT
    2005 DR 650

  4. #4
    Registered User
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    Jul 2010
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    Tularosa, NM
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    Valve guides. . .

    Valve guides would be my guess, too. "Supposedly" you can diagnose this by noting the light blue smoke as you roll OFF the throttle. "Supposedly" you can diagnose an oil-ring problem by noting the smoke on acceleration. This eyeballing in the rearview is OK as far as it goes, and is accurate, as far as it goes.

    However, given that you've got it apart, I'd pop the valves loose and give the stems a wiggle in-place (obviously w/o being attached) and see what you detect. I'd guess that your intakes will show little movement, and (maybe) exhausts will display some movement, and you'll feel a definite difference. You can then either measure everything yourself, or take the bits to a machine shop, find out the exact numbers, and compare to spec. The "wiggle" test is just a guideline, but a pretty good one -- the stems shouldn't move very much, at all, if the guides are healthy.

    Some of us are more tolerant of laying down a smokescreen, some less. Personally, I don't like it! Good luck, and let us know what you find.

    Walking Eagle

  5. #5
    Registered User ebeeby's Avatar
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    Re-orient the rings and button 'er up. Problem solved.

  6. #6
    Registered User
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    Apr 2012
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    Draper VA
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    46

    You Tube

    One of the Chris Harris Affordable Beemer Service videos shows how to check valves with an air hose.

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