BMW G650X Challenge Thread Index

Discussion in 'Thumpers' started by GB, Apr 24, 2008.

  1. cpallen

    cpallen Nearly Adventurer

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    And when driven by the motor in gear does the sprocket or bolt head turn? Or does the motor free wheel?

    I’m hoping that the bolt is broken - else may be clutch?
  2. MJS

    MJS Long timer

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    couple of possible things.

    Stripped splines on sprocket or output shaft.
    Slipping clutch (more than slipping if there's no drag)
    Internal transmission failure.

    "put it in gear and the front sprocket is just spinning" "When I try to loosen the bolt, it just turns, but the sprocket doesn't. Even in gear, so I don't think it's the sprocket. Thats why I was asking how can i get the sprocket off. There's no way to loosen the bolt."

    This is somewhat contradictory. If the bolt turns but not the sprocket I would suspect #1. But you said the sprocket was spinning. You should feel resistance of the motor when in gear and turning the bolt.

    Put the bike on a stand or have someone hold the bike on the side stand with the rear wheel in the air. Put the bike in gear and try turning the back wheel? Does the wheel turn freely or does it try to turn the motor over?

    As for removing the bolt, without the chain and rear brake to hold the shaft you're going to have to use an impact wrench against the motor compression. Make sure you're in first. If it still spins try 2nd or 3rd to be sure you're in gear. A stripped bolt would be my hope for an easy repair but likely to be stripped output shaft splines as the sprockets are harder material.

    Be sure to grease the sprocket and output shaft splines. I like severe duty synthetic grease (i.e. CV grease). Does not have to be high speed (wheel bearing) grease, impact resistance is more important. Lack of grease will cause spline damage. The grease is needed because the sprocket moves on the shaft. The bolt does not provide enough pressure to prevent movement. It would require a big press to install or remove the sprocket if the fit was tight enough to prevent any movement between the sprocket and shaft.
  3. cpallen

    cpallen Nearly Adventurer

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    @MJS provided a detailed answer. I'm not sure I understand what is and what isn't happening with respect to the bolt and sprocket either. The sprocket shouldn't turn without the wheel and chain turning with it. The bolt should turn with the sprocket and if it turns independently of the sprocket you need to determine if the wheel/sprocket will turn with the transmission in gear (lift rear tire off ground leaning over on the sidestand) or is also free wheeling. Here's some pictures and diagrams that might help.

    Countershaft sprocket Image.PNG Countershaft sprocket parts.PNG Transmission exploded diagram.PNG

    It does sound like either the bolt is broken or the splines are stripped. I hope it's something simple.
  4. 84ceejay

    84ceejay Been here awhile Supporter

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    Sorry need to rephrase. I broke down in Gerlach, NV over 100 miles from my truck, so I was a little frazzled. The sprocket does not move when in first gear. I can turn the sprocket retaining bolt either direction, the bolt turns but the sprocket does not. I can also push the bike while in first gear and makes a grinding noise, it does however shift into neutral and show the neutral light. I have not tried any other gears other than first. Thank you all for your input. I don't think the outcome is good, but sure had a great riding day in North Nevada until this!
  5. cyclopathic

    cyclopathic Long timer

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    Most likely stripped threads on the bolt which you likely were turning in wrong direction
  6. cpallen

    cpallen Nearly Adventurer

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    I guess that next steps (after getting the bike to a good place to work on it) would be to remove the rear wheel and free the chain from the sprocket and see if you can pull the sprocket off the shaft, with the bolt intact.
  7. 84ceejay

    84ceejay Been here awhile Supporter

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    At the time, I thought the bolt might be loose. There's no way I could have stripped the bolt. I didn't put enough torque on it to strip it.
    cyclopathic likes this.
  8. 84ceejay

    84ceejay Been here awhile Supporter

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    Thank you cpallen. I will try that tomorrow.
  9. cpallen

    cpallen Nearly Adventurer

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    With any luck the bolt broke, and the splines on the sprocket stripped and not the splines on the shaft. Do you know if it is an OEM BMW sprocket, or an after market item?
  10. 84ceejay

    84ceejay Been here awhile Supporter

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    No, I have no idea. I just got it home. I'll have to look tomorrow. Just really thankful it broke in town. Been riding back roads with no cell service all weekend.
    advFord likes this.
  11. cyclopathic

    cyclopathic Long timer

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    If bolt turn with the shaft and sprocket not then stripped splines but then first gear isn't a really engaged which is likely. You would need to rotate shaft while pressing on shifter down to engage gear and Rotax isn't the best engine for that as chain and shifter on opposite sides.

    Another possibility that bolt undid itself and sprocket jumped off the splines. Regardless 1st gear isn't engaged.
  12. Gravel Seeker

    Gravel Seeker Old, growing older.

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    You've tried to lock the rear wheel-chain-sprocket-engine by engaging rear brake and then trying to loosen the bolt? If bolt moves independently of sprocket/shaft then it probably won't be useful to use the rear brake.

    You can turn the engine (or apply oposit pressure) with a large Allen key (#10?) in the hole on the stator cover (right hand side, behind the plastic plug). With a larger arm on that you might have luck locking the engine rather than compression if you try 2nd or 3rd instead of 1st (might even be a good option even in 1st if you have internal damage to the drive train?)
  13. MJS

    MJS Long timer

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    The neutral switch has a plunger which rides against a shaft inside the transmission. While not a common problem, if the switch is worn or broken the plunger can cause shifting / gear engagement issues. Switch is located in front of the cs sprocket (below #3).

    [​IMG]
  14. 84ceejay

    84ceejay Been here awhile Supporter

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    Held the washer with vise grips and got the bolt out. Not good news.

    Attached Files:

  15. cpallen

    cpallen Nearly Adventurer

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    That does not look good.
  16. 84ceejay

    84ceejay Been here awhile Supporter

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    Nope, not at all. Thanks for the help. At least it's wintertime....
  17. tbarstow

    tbarstow Two-wheelin' Fool Super Supporter

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    Ouch. You're the winner of a case splitting repair!
    DGR likes this.
  18. cyclopathic

    cyclopathic Long timer

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    Part 23007699857 for a mare $428.54 bummer. Makes me wonder if you can find someone to weld and machine it for less.
    gnarlynate24 likes this.
  19. tbarstow

    tbarstow Two-wheelin' Fool Super Supporter

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    You can replace the motor for $1300 on Ebay. Look for a Sertao motor.
    Snake Oiler likes this.
  20. cpallen

    cpallen Nearly Adventurer

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    or just weld a new steel sprocket onto the shaft?
    advFord likes this.