r100gs -91 vibration at 3000-3500 rpm

Discussion in 'Airheads' started by KaaJa, Jun 28, 2016.

  1. 190e

    190e Long timer

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    Those are good pressures and remarkably consistent across the two cylinders.
    #21
  2. KaaJa

    KaaJa Been here awhile

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    Still haven't done leakdown test, but have done several other things.
    Cleaned carbs, disassembled and cleaned beancan, checked timing obviously, balanced carbs and tinkered with mixture.
    Checked valve clearance and adjusted rocker endplay.
    Checked for airleaks and found none.
    On idle it is running very roughly no matter what I do, kind of misses occasionally. Right sparkplug is soothier than left. I changed plugs about 150 km ago.
    Today coming home from my garage it was vibrating as it was earlier, I think it is doing it even broader revs, about 3000-4200.
    I think next step is taking engine apart again...
    #22
  3. CheckerdD

    CheckerdD Long timer

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    I would not take the engine apart. I think the guy who told you about the springs in the bean can got it right. Its worth switching the can if you can find another one. I would even go out and buy a new one to avoid another tear down. Dave
    #23
  4. HydroPnik

    HydroPnik Adventurer

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    Try retorquing the engine mounts - 55 ft/lbs, I believe. I had a similar vibe and retorquing them got rid of it.

    Edit - I see you already did this.
    #24
  5. KaaJa

    KaaJa Been here awhile

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    There is quite more carbon buildup on right cylinder and sparkplug than left. Could that cause vibration?
    It uses little bit of oil, I'll have to measure how much after next oil change.

    I've checked drive shaft bolts and they were tight.
    I have little concerns about my transmission build. It shifts very rough and there is little bit of metal on the magnet even after about 500km. I'm going to lok into that soon.

    I rode my friends r100gs and it got little vibes on same region on engine braking but just little, it didn't bother me at all. And transmission was very smooth compared to mine...
    #25
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  6. tsADV

    tsADV Been here awhile

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    When checking the carbs, did that include the choke/enricheners/auxiliary carb circuits as well - ? If slightly open, the aux carb could well result in one sooty plug, but not necessarily RPM related vibration.
    You didn't mention anything about a transmission job in your initial post in this thread. Did the 3-3.5 kRPM vibration issue begin well _after_ the transmission work?

    If not, you didn't happen to remove the clutch assembly when looking at the gearbox? A few years ago, my 80/7 began vibrating at 2.5-3 kRPM after I replaced the clutch pressure plate, without having paid attention to the angular positioning (balancing) of the clutch components. Now sorted out after fitting a balanced flywheel/clutch assembly; but I wonder how much potentional vibration problems there are with the lighter post-81 clutch carrier assembly, compared with those associated with the heavy flywheel job used up to 1980.
    #26
  7. KaaJa

    KaaJa Been here awhile

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    #27
  8. KaaJa

    KaaJa Been here awhile

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    Well. One guy from our Finnish forum just send me email about vibrations on his 100gs, he has same pistons as I and he has same vibrations on same rev range so I think this is settled.
    I just have to address the gearbox issue and keep the revs higher.
    Thanks to everybody that helped, this is such a great community!
    #28
  9. KaaJa

    KaaJa Been here awhile

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    Checked my new driveshaft just for curiosity and found that it had twisted alot already. Shaft has about 6000km.
    [​IMG]
    [​IMG]

    Here is new and old side by side. Old is lot less twisted and has to my knowledge about 125000km.
    [​IMG]

    I can see mono or 1100 conversion in my future...
    #29
  10. KaaJa

    KaaJa Been here awhile

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    Vibration still exist. Its worse on engine braking at about 3000-3500 rpm and low speed offroad stuff on same rev range. It is really annoying, and can be felt on footpegs and on seat.
    After last post I have changed:
    -35000km driven bmw cylinders and pistons with new rings,
    -new valve springs
    -new diaphgrams on carburetors, left had little hole on the outer edge,
    -left head had intake spigot loose, tightened that with locktite,
    -new silent hektik coil and wires
    -stainless collector
    -new driveshaft

    Any suggestions? I'm getting really frustrated.
    #30
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  11. Dreossi

    Dreossi Been here awhile

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    Forgive me if this has already been suggested, and likely you've done this already-- have you re-checked the paralever bushings, at both ends, for correct seating, preload, and torque?

    I had a vibration in the pegs of my gs, and after check-over and torque-up, it was fixed.
    #31
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  12. Big Bamboo

    Big Bamboo Aircooled & Sunbaked

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    Another thought; you mentioned something was weird with the timing. I worked on a GS recently that had one of the advance weights in the bean can rusted solid, but the other was moving. It showed advance, but was stumbling. Might be time to have a look see. Note; you don't have to pull the can apart to check. Just remove the little side plate and check that the weights are free on their pivots through the hole.
    #32
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  13. bmwrench

    bmwrench Long timer Supporter

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    Your right plug shosw an oil control problem. What sort of rings do the Wossner pistons have?

    You said you balanced the rods-did you balance the pistons? Finally, at 9.5:1, you've raised the compression substantially, and this increases vibration.
    #33
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  14. KaaJa

    KaaJa Been here awhile

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    Ignition is now Silent Hektik, installed that already last summer, I've binned the wössners and pistons are original bmw 8.5:1. Pistons were within 0,5g the same weight.
    #34
  15. KaaJa

    KaaJa Been here awhile

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    Vibration goes away when I pull the clutch while riding in the vibration zone. If I revit while clutch is pulled I can feel the vibes too.
    #35
  16. KaaJa

    KaaJa Been here awhile

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    I changed 32mm bings to rule the carbs out. No change, although it runs and starts better.
    How bad vibes can clutch carrier make if out of balance?
    #36
  17. Prutser

    Prutser Long timer

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    I just made a 4500km trip and my bike was starting to run worse and worse every day. It turned out to be one exhaust valve which lost it's clearance way too fast.
    My bike had a lot of similar problems as you described. I totally didn't expect this so went through all other things just like you.
    Because I checked the valve clearance just before I started the trip i never thought about the tight valve. The 15.000 km i drove with the bike before never showed signs of the valve sinking into the valve seat.
    #37
  18. Gisslaboda

    Gisslaboda Adventurer

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    I would be interested in hearing if you ever got to the bottom of this vibration problem. I have a similar problem on my R80 GS, 1991. But the clutch does not play any part in the problem.
    Thanks
    #38