Not sure what broke?

Discussion in 'Motorized Bicycle Trouble Shooting' started by CRP, Feb 28, 2017.

  1. CRP

    CRP Member

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    I haven't taken the bike part yet but here's my problem.

    I have a Hasheng 4G transmission and what has happened is the sprocket that drives the chain doesn't seem to be connected any more. It won't drive the chain. The nut is tight but it seems the sprocket has some how become disconnected to the shaft? Without taking it apart I'm not sure how the shaft connects to the sprocket? Is there some sort of bearing in there?
     
  2. Greg58

    Greg58 Well-Known Member

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    This sounds like a sheared key, some of the key stock that is supplied with kits seems to be very soft.
     
  3. MotorBicycleRacing

    MotorBicycleRacing Active Member

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    You probably have the 12 tooth freewheel 4G version.
    Sounds like the freewheel is destroyed if it rotates in both
    directions and doesn't turn the chain.

    The freewheel is keyed to the shaft.
     
  4. CRP

    CRP Member

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    So just try to pull the sprocket off and look for a damaged key?

    I'll pull the sprocket and see what happened. It does rotated freely in either direction.
     
  5. Greg58

    Greg58 Well-Known Member

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    As was posted you may have destroyed the free wheel or the key, either way you need to take it apart.
     
  6. CRP

    CRP Member

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    Finally got to fixing the bike. The key is ground down to nothing.

    What size key and where would I get one?

    I don't see a channel or groove on the shaft, you just put a key in the channel on the sprocket and hammer it in and that holds the sprocket and shaft together? It just doesn't seem like enough to hold it together to me?
     
  7. Greg58

    Greg58 Well-Known Member

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    The key is either square stock or half moon type, look close at the shaft to locate the remaining part of the key. If you kept running the engine after the key sheared the shaft may be damaged beyond repair. You will probably have to dig the old key out.
     
  8. CRP

    CRP Member

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    I don't see the key at all in the shaft. It looks smooth all the way around. I'll look again. My son was running the bike and it it just basically stopped turning the sprocket. I guess the key sheared then the motor was still driving the shaft while the sprocket stayed still.
     
  9. CRP

    CRP Member

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    I could barely see the end of the key. I could not dig it out. In the end I used a dremel tool and ground it out. Found a woodruff key that was close to the right size at a auto place and then I used a grinder to get it to fit. I little work and I'm set to go I think.

    It was a square key to begin with I think. That's what is in there now and it seems to holding.

    The top is a prefect fit but the bottom is close but between a grinder and dremel tool it's not prefect. That won't be a problem will it? These things don't have to fit exactly together to work, right?
     

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