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Chainring wobble

Old 07-08-20, 09:38 PM
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Solo_rider
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Chainring wobble

Hi.

I have a bike that I'm trying to sell but it needs some work. The main thing I noticed was that the chainring wobbles and at one point the chain rubs against the chain cage when it's on the largest ring. Looking at the chainring I can't see any bending but I'll have to re-check. If I pull on the crank it doesn't feel like it's loose. I'm trying to find out what the problem is and where I should be looking. It's a Truvativ crankset (bike is probably around 5 years old looking at the model). I don't know anything about the history of the bike.

Any help will be appreciated.
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Old 07-08-20, 09:58 PM
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Originally Posted by Solo_rider View Post
Hi.

I have a bike that I'm trying to sell but it needs some work. The main thing I noticed was that the chainring wobbles and at one point the chain rubs against the chain cage when it's on the largest ring. Looking at the chainring I can't see any bending but I'll have to re-check. If I pull on the crank it doesn't feel like it's loose. I'm trying to find out what the problem is and where I should be looking. It's a Truvativ crankset (bike is probably around 5 years old looking at the model). I don't know anything about the history of the bike.

Any help will be appreciated.
best way to check if a chainring is flat is to remove it and place it against a sheet of glass, a mirror, or similar. If the ring is flat, then the problem lies with your crankset or BB. Donít know an easy way to test for a bent crank, but if you remove it, you might be able to see a bent BB spindle by spinning it
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Old 07-08-20, 10:57 PM
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Originally Posted by Litespud View Post
best way to check if a chainring is flat is to remove it and place it against a sheet of glass, a mirror, or similar. If the ring is flat, then the problem lies with your crankset or BB. Donít know an easy way to test for a bent crank, but if you remove it, you might be able to see a bent BB spindle by spinning it
Sure sort of, But this check is based on a non reality. As said the real world of a ring is as it's mounted on the crankset. So it doesn't really mater whether the ring is flat when off the crank arms. You have to deal with the world you are in.

It's pretty common to align rings while spinning the cranks while using the ft der or a piece of tape standing off the frame as an indicator. Whether one bends the ring or the spider arms is the trick. Also how.

One can bend the ring or arm in or out with various levers or impacts. Or twist the ring between the arms with two tools. Rather simple blacksmithy but takes some practice to become comfortable in doing whatever improvements can be had. And that's the take away. Not all rings are able to be perfectly aligned but a lot can be made better. Andy
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Old 07-09-20, 02:47 AM
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Thanks for the replies. I appreciate it. I've actually watched some videos on Youtube showing how to bend a ring back to a straight position but I wasn't sure that was my problem since the ring didn't really look like it was bent. So, I was thinking maybe it is a BB problem. I guess I'm gonna have to take it off the bike and take a closer look....that's IF I can do that. I've never taken a chainring off a bike before. Wondering if I need special tools or something or it's just removing the 5 hex screws that I think are holding it in place.
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Old 07-09-20, 12:27 PM
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Are you certain that the crank is properly torqued onto the BB?
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Old 07-09-20, 01:54 PM
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My chain ring wobbled because the BB was not torqued correctly and was very slightly loose.
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Old 07-10-20, 02:23 AM
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Originally Posted by themp View Post
My chain ring wobbled because the BB was not torqued correctly and was very slightly loose.
Originally Posted by due ruote View Post
Are you certain that the crank is properly torqued onto the BB?
No. I don't know. I know this bike has been neglected by the previous owner. Thanks for the info. I still haven't tried taking the crank off.
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Old 07-24-20, 04:23 PM
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So, I'm going to attempt removing the cranks but this is a first for me. I just bought the proper size hex key but I'm assuming I need a crank puller tool. Or is there a way around it ?
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Old 07-24-20, 11:38 PM
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Originally Posted by Solo_rider View Post
No. I don't know. I know this bike has been neglected by the previous owner. Thanks for the info. I still haven't tried taking the crank off.
I also faced a similar problem of the drive crank not seated properly on the BB spindle even though it was tighty bolted. Removed and reinstalled (in a different angle/notch on the spindle) and wobble disappeared. Note if you're going to install in a different angle, you'll need to remove the other crank too.
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