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Old 02-01-11, 02:52 PM   #1
scozim 
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Bent steel ring? Cottered crankset

I know some cranksets I've had in the past have had a little side to side movement, especially when I mash on the pedals or am standing while climbin.

On the late 60's Gitane I just finished I was doing some fine tuning and noticing that the crankset seems to have some wobble in it as it rotates around - no pedalling, just spinning it around. Probably a 1-2 mm - can't get a real accurate measurement. I can usually see it fairly well sighting straight down and using the front derailleur cage as my gauge. Wondering if I might have a slightly bent large chainring.

Any advice on how to accurately check the ring. I tried a level but that didn't seem to work too well. it's a 5 pin crank and the two rings don't separate - just the arm.

Here's a photo of the crankset - I like it because of the 52-36 gearing.

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Old 02-01-11, 03:05 PM   #2
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I have bent steel chainrings back toward alignment visually by spinning it slowly and seeing where it moves out of alignment and then bend appropriately and judiciously, using Park Tool BT-3.
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Old 02-01-11, 03:19 PM   #3
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A zip tie around the seat tube or down tube makes a handy reference point. Zip it pretty tight and cut the tail down to about 2". I have a pic somewhere but you get the idea.
Here it is, just do it closer to your crank and farther from your wheel.
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Old 02-01-11, 05:29 PM   #4
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I have straightened out a few bent ring sets in my time. I took a couple of pictures and sort of describes the process in this page from my Legnano Nocostalotta feature article on MY "TEN SPEEDS".

Hope it helps a bit.
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Old 02-01-11, 05:58 PM   #5
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Nice crank!
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Old 02-01-11, 06:23 PM   #6
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Quote:
Originally Posted by Peter_B View Post
I have bent steel chainrings back toward alignment visually by spinning it slowly and seeing where it moves out of alignment and then bend appropriately and judiciously, using Park Tool BT-3.
A difficult tool to find -you can't even find it on the Park Webpage.

I just use an adjustable wrench and I think most people do, which is why park doesn't even bother to market this tool any more.

One could make one out of a piece of 1" x 1/4" steel bar and a chop saw to make a notch at the end easily enough.
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Old 02-01-11, 06:24 PM   #7
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Assuming a correct setup, if it's warped, I'd pull it off, put it on a flat surface, and use a wedge (wooden) to lift the "low" section a bit. If it's on the edge, do what I do with bent teeth and get a BFW (adjustable, preferably), and give it a twist.
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Old 02-01-11, 06:50 PM   #8
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Originally Posted by mickey85 View Post
Assuming a correct setup, if it's warped, I'd pull it off, put it on a flat surface, and use a wedge (wooden) to lift the "low" section a bit. If it's on the edge, do what I do with bent teeth and get a BFW (adjustable, preferably), and give it a twist.
The BFW indeed.





I didn't do so well with my odDyssy of straightening a chainring. I bent it little by little, got it just about "right" and then I tried to get it a little more "right" and it was wrong from then on out.
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Old 02-01-11, 07:30 PM   #9
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I have had one get so far out that is sort of potato chipped. I think the circumference got a little more stretched than the middle. I could pop it from left to right but I couldn't get it to stop in the middle.
That one got a chain stuffed between it and the other ring to start things off. I had to just start over with a fresh ring.
Other rings I've had good luck with, though.
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Old 02-01-11, 07:42 PM   #10
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You can use the front derailleur cage as a guide. Lower the derailleur until the cage is barely touching the big ring and bend a little section at a time. I've done it many times. Soczim, are you going to the Seattle Bike Swap this year?
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