Bent steel ring? Cottered crankset
02-01-11, 02:52 PM
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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.
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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1984 Gitane Tour de France; 1968 Peugeot PL8; 1982 Nishiki Marina 12; 1984 Peugeot PSV; 1993 Trek 950 mtb; 1983 Vitus 979; Colnago Super, mid-80's Bianchi Veloce, 1984 or 85 Vitus 979
02-01-11, 03:05 PM
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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.
02-01-11, 03:19 PM
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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.
Here it is, just do it closer to your crank and farther from your wheel.
02-01-11, 05:29 PM
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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.
Hope it helps a bit.
02-01-11, 05:58 PM
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Nice crank!
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02-01-11, 06:23 PM
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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.
02-01-11, 06:24 PM
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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.
02-01-11, 06:50 PM
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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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02-01-11, 07:30 PM
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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.
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.
02-01-11, 07:42 PM
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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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