Problem: Chain comes off sprocket

Discussion in 'Motorized Bicycle General Discussion' started by 1dave1, Jan 29, 2013.

  1. 1dave1

    1dave1 New Member

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    Hello all,

    I just completed my second build, a 26 inch beach cruiser w/ 80cc engine. Everything came together great but I had the same problem I had before, the chain keeps coming off the sprocket onto the spoke side. I looked closely and it appears that it starts to come off from the bottom and then works its way all the off quickly. Its also a real pain because I have to thread the chain out of the spokes. Everything looks pretty good in terms of alignment and chain tension to (a little loose but not much).

    Last time I took my bike to this guy in San Diego and he fixed the problem. I believe that he fixed my issue by putting a 50 or 52 tooth sprocket onto the wheel. I could be wrong though because he had it already to go when I came by his house. I might just take that sprocket off and place it on the new bike. ****, I might just take off the whole wheel and put it on the new bike. My issue w/ that is that the new bike is 7 speed, old bike is single speed. New bike also has sweet red rims :)

    Would a sprocket w/ more teeth help my problem? Any other suggestions?

    Thanks a ton guys.
     
  2. WightBoy

    WightBoy New Member

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    You could still run the other rim on that bike if the frame is steel. I went from 7 speed to single. Check to see if the sprocket wobbles side to side when spinning the wheel. that may cause this issue.
     
  3. 2door

    2door Moderator
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    I know you say the alignment "looks pretty good" but this is a classic symptom of improper alignment between the engine drive sprocket and the rear wheel driven sprocket. How are you checking the alignment? You need to lay a straightedge on the two sprockets and sight from the rear looking forward.
    Roller chains will not run well if the sprockets are not in line with each other. Chain tension is also important. 1/2 to 3/4" slack.

    Are you using a chain tensioner? If the tensioner bracket wasn't bent/twisted to align the tensioner wheel with the chain path then it might be pulling the chain off to one side. That too can be seen from the rear looking forward. Every component of a chain drive must be aligned with the other parts.

    Sprocket size/number of teeth has no influence on chain alignment. It only determines the final gearing.

    Tom
     
  4. 1dave1

    1dave1 New Member

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    Thanks Tom. I think you are right on. I'll cut a few links out of chain (to get that tension you spoke of) and then I'll see if everything lines up. If so, I'll give it a go and let you know what happens
     
  5. The_Aleman

    The_Aleman New Member

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    Like Tom said, that bracket does need a little twist in it on most bikes for it to work properly. Make sure the chain enters and exits the wheel straight.

    Done properly and chain not set too tight, it should track perfectly as long as your engine and sprocket are straight.
     
  6. 2door

    2door Moderator
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    Also as was mentioned above by Wightboy, sprocket concentricity and lateral alignment is also critical. The rear sprocket can not have any wobble either horizontally or vertically. It must run true with the rear hub as viewed from the side and the rear. Wobbling will derail the chain as easily as misalignment.

    Tom
     

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