Grubee Freewheel Sprocket Failure

Discussion in '4-Stroke Engines' started by Irish John, Aug 26, 2008.

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  1. Irish John

    Irish John Guest

    I wonder has this happened to anyone else. My freewheel grubee sprocket failed after 150 kms. The whole assembly became loose and the ratchet mechanism failed. I took it apart - quite interesting to see how it's made - very fragile really and I wonder how the tiny ball bearings could last when they weren't sealed in place properly. I think when it came loose the grease must have come out and the whole think disintegrated.
    Don't know how it came loose cos the sprocket is held together by a revers threaded flange on the inside and a bolt holds it onto the shaft.
    Disappointing thing to happen to my lovely new Billinudgel Bullet. It's not quie as bulletproof as I thought and I'll have to make another key for it and they are tiny little things with rounded ends.
    There is a tiny wire circlip that goes around the middle of the assembly but I can't figure out just how it should go back together.

  2. HoughMade

    HoughMade Guest

    Wow- sorry to hear that. I look forward to you reports on solving this problem....for when I have to.
  3. Irish John

    Irish John Guest

    This sprocket isn't fixable cos I think it's been mangled too much and lost a couple of ball bearings. I'm posting it back and he's posting me a replacement.
    No I won't. I'll take it apart and photo it for MBc posterity cos I'm sure if the pics are good one of you guys will understand how it all works.
    Then I'll post the info up here so we can study this little beast.
    Then I'll post it.
    Last edited by a moderator: Aug 26, 2008
  4. Irish John

    Irish John Guest

    How the freewheel sprocket works

    Here are pictures of the innards of the freewheel sprocket. I think I assembled it correctly but I could be wrong. I do know, however, that the ball race flange that holds the whole thing together should be loctited in very securely because it came loose and that is what caused this sprocket to fail at 150 kms. Those bearings fall out through a very small gap but I think they are easily available from a good bike shop.
    I'm posting these pictures because I am sure they will be useful to other Grubee owners. Many suppliers will only supply a replacement sprocket attached to the rear gearbox casing, the final drive shaft, the engager and cable (but not the gearbox to engine gasket). This isn't very good service when you only want a freewheel sprocket.
    Lastly, remove the old sprocket with small 3 jawed gear pullers (100mm size) and do not put it back on the keyed shaft with rubber hammer blows. I think it needs to be squeezed back on in a vice cos it won't just slide on using hand force. The key has to be a very good fit and that usually means it will be very tight.

    Attached Files:

  5. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member

    Thanks, great info
    Could you please post a pic of the shaft that the freewheel goes on? ( with the freewheel removed)
    And give the dimensions of the shaft?

    Thanks again
    Last edited: Aug 26, 2008
  6. Proboscis

    Proboscis Guest

    Is there anywhere I can buy a replacement. I had mine seize up.
  7. Pablo

    Pablo Motored Bikes Sponsor

    Very similar to Dicta construction. Which is also not bulletproof. To some extent it's the nature of a low resistance freewheel. (and trade off for cost vs. tolerance)

    Good pictures.
  8. Proboscis

    Proboscis Guest

  9. Irish John

    Irish John Guest

    Sprocket Shaft diameter & Keyway.

    It's not a woodruff key Proboscis it's an ordinary straight key and it's 3mm wide. The shaft is 10.5mm dia.

    Attached Files:

  10. Proboscis

    Proboscis Guest

    Irish John. I'm Portuguese :) Oh do I wish it held up on the first day, sheered right off that key.
  11. Irish John

    Irish John Guest

    Potugese Proboscis, are you telling us you welded it the wrong way around? It's tempting to weld but the sprocket is not that good and the weld is if you get my drift.
    It's no big deal to make a key from a length od 1/8" key steel. Every pass of a flat file really shaves it down fast so you have to take care cos before you know it you can file off too much steel. I could make one without a vice and just filing it in my hand.
    I would like to know how you got your shaft out of the gearbox and how you got the other engager key out of the shaft?
  12. MasterLink

    MasterLink Member

    this haapind to me i lost a few bearings it was a nightmare geting it to work again but i got it working and ordered a back up the ball bearing count is important i think it was 24 a side and needs to rachet when back together to tighting it up i put it in a vise and took a big nail and a hammer and got it tight as i could it worked here is the link where i got my back up .
    its not listed but call jermey and ask him for one i think its like 20 bucks shiped here is the link i started
    about it i was told by jermey that he see this a lot if the chain is to tight on you bike ...
    loctight needs to be put on that 8 mm bolt ohh as a side note i bent that drive rod holding it to get the bolt lose its very soft i ordered one of thos also Proboscis hes has it also 15 bucks call him and ask ...i want that the drive train to run very true
  13. loquin

    loquin Active Member

    Possibly, you could get one of staton's adapters, & a standard freewheel sprocket.