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Loose front sprocket on BMX
#1
My son has a Redline BMX bike and he noticed the front sprocket is wobbling side to side. I looked at it and can not figure out what has changed from when it was a new bike not long ago. I cannot find anything that will tighten or adjust the sprocket. I have searched on the internet but can only find front sprockets that have a bolt that connects the sprocket to the crank. Unfortunately I don't believe his is set up that way. It does not seem to have a bolt that connects the sprocket to the crank like many I have seen. Does anyone have any solutions or ideas that would help me? Thank you for any help! Oh and by the way I would take it to the local bike shop where I bought it but they are closed for the winter and have not reopened yet. He is wanting to get out and enjoy the sunshine so any help is appreciated.
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#2
Any pictures would help some. Smile
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#3
I went out to take some pictures and of course the camera battery was dead. I am charging it and will get some pics posted tomorrow evening after work. Some info that might help is that there is a round metal cylinder shaped piece protruding out from the crank that goes through a round hole in the sprocket. Thanks for the help!

Mike
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#4
(02-21-2011, 05:15 AM)plow509 Wrote:  I went out to take some pictures and of course the camera battery was dead. I am charging it and will get some pics posted tomorrow evening after work. Some info that might help is that there is a round metal cylinder shaped piece protruding out from the crank that goes through a round hole in the sprocket. Thanks for the help!

Mike

I think I know what happened, BUT as name said we'll see in the pictures. Really just wanted to say welcome to the forums. Wink
Good maintenance to your Bike, can make it like the wheels are, true and smooth!
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#5
This sounds like a one piece crank (opc).
Either the chain ring is bent, which you should be able to see visually when rotating the cranks, or, the bearings or the chainring locknut is loose, which you should be able to feel by shaking the crank arms.
Bent chain rings are not covered under warranty, as this is damage, you may be able to straighten by gently bending in the opposite direction with a wrench or similar, if this fails a new one will be required.
Loose bearings or lock nut needs a complete dismantle of the bottom bracket and should be covered under warranty, but is fairly complicated if you are not mechanically minded, when does the shop re-open as they should do it foc.
If its a 3 piece crank, the right hand crank arm is loose and needs tightening, again under warranty.
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#6
Thanks for the info Trev. I am pretty sure it is not a one piece crank setup and I can't see that the sprocket is bent at all. I finally have pics so that may help. (I hope) Thanks to all for the info and I'm sure we will figure it out soon.
Mike
[attachment=1940]
[attachment=1941]
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#7
Any more help is greatly appreciated.
Mike
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#8
(02-22-2011, 09:37 PM)plow509 Wrote:  Any more help is greatly appreciated.
Mike

Googled your problem. Might want to service it up.

http://www.parktool.com/blog/repair-help/bmx-three-piece-crank-service

There's a guide on park tool's webpage showing how to do it.
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