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Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

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Old 10-26-10, 09:30 PM   #1
Tony Pham
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odd scratching like noise from crank?

At least I think the noise is coming from the crank. Ever since I had to replace the tube in my back tire it's been sounding odd. For one I couldn't perfectly fit my back tire on. The side of the axle with the crank fit well into the frame's notch but the other side wouldn't go in all the way -- if that is at all specific enough imagery.

Anyway, whenever I pedal now the crank makes an odd scratching noise when I pedal down. It's less noticable at higher gears.

Any idea?
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Old 10-26-10, 10:06 PM   #2
Jeff Wills
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Originally Posted by Tony Pham View Post
At least I think the noise is coming from the crank. Ever since I had to replace the tube in my back tire it's been sounding odd. For one I couldn't perfectly fit my back tire on. The side of the axle with the crank fit well into the frame's notch but the other side wouldn't go in all the way -- if that is at all specific enough imagery.

Anyway, whenever I pedal now the crank makes an odd scratching noise when I pedal down. It's less noticable at higher gears.

Any idea?
The axle shouldn't be all the way back in the dropout's slot. It should sit vertically above the rear derailleur's pivot.

Scratches and creaks can be heck to track down without having the actual bike up on a workstand- and then it might take several tries and test rides to find the problem and fix it. Get the rear wheel in the proper place first, then take the bike to a bike shop if that doesn't fix things.
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Old 10-27-10, 05:59 PM   #3
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thanks. is there a picture of video which could illustrate this as well?
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Old 10-27-10, 07:33 PM   #4
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actually it's more like a creaking noise if that is more diagnosable
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Old 10-27-10, 07:40 PM   #5
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Make sure the noise isn't coming from a pedal. Sometimes, dry pedal bearings make sounds that make you think they're coming from the BB.

The wheel does need to be in straight. You need to sort out why one side isn't getting into position.

Try again, and describe what you find.
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Old 10-28-10, 06:28 AM   #6
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From your initial description, it sounds like you have a slot-mounted derailleur, as opposed to one that mounts on a separate hanger. If that is correct, the side opposite the crank will NOT go in 'all the way'. It should sit forward of the rear of its slot an amount equal to the space required by the slot-mounted der. If it IS a hanger mounted der. then the axle should be equally inserted in both slots.

As far as creaking noises, there are many more sources than cranks and pedals--I had one that was driving me batty, and finally tracked it down to my seat post clamp! Good luck finding yours.
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Old 11-01-10, 06:54 PM   #7
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i received another flat tire and replaced it again. this time it doesn't make a peep. guess i didn't align it right the first time
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Old 11-02-10, 07:56 AM   #8
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One common source for a "scratching" sound in the bottom bracket is when someone forgets to remove one of those little red Shimano alignment gauge sticker thingies from the front derailleur. This is most likely to occur with a customer that has a comfort or entry level bike with a plastic chainguard ring.
I don't know what top-secret military/aerospace material these stickers are made from, but they are indestructible. They never fall off on their own and seldom tear. I had a lady bring in a Giant hybrid yesterday with about 6500 miles on it. The little red sticker was still on the front derailleur, intact, readable, and a little dirty.
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