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Singlespeed & Fixed Gear "I still feel that variable gears are only for people over forty-five. Isn't it better to triumph by the strength of your muscles than by the artifice of a derailer? We are getting soft...As for me, give me a fixed gear!"-- Henri Desgrange (31 January 1865 - 16 August 1940)

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Old 11-22-05, 09:24 PM   #1
hamandcheese
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Chainring off center

So I can't get my chainring to stay on centered. I first slapped the thing on and the chain tension varied from almost too tight to turn, to almost too loose to stay on, depending on where in the crank arms rotation it was. I figured out how to center it (with a sugguestion from the guys at counterbalance) but when I get home from riding the thing is always off center. This is eventually going to lead to the chain either coming off or the wheel seizing up. I'm cranking the ring bolts on as tight as I can. I do only have a little set on allens for this but it seems pretty f'in tight.

When I first fixed the bike, I was running the original 52 chainring with a 17 in the back and I never had this problem. I just switched to a 46-16 and now this... and I have tried it with the 17 to try and narrow it down to either the cog or chainring. It seems to be the chainring (or possibly cranks)

Any ideas on how to get this straightened out...?

PS Its a Vuelta chainring. Not the best thing invented but it shouldn't be that lopsided should it?
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Old 11-22-05, 09:31 PM   #2
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No chainring is perfectly circular and cheap ones are even less so.
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Old 11-22-05, 09:35 PM   #3
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how did you 'center' it ?
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Old 11-22-05, 10:07 PM   #4
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I'm actually having this same problem With my IRO crankset, albeit to a lesser degree. I followed the Sheldon Brown method - but I can't seem to tap it centered. As is stands now, It goes from 1/2" of play at the tightest gradually to 3/4" of play at the loosest. It's not really grinding, but it's not dead quiet either. I think I'm going to take it to a LBS to see if I can get a better understanding of how to do it, unless there's a better way.
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Old 11-22-05, 10:13 PM   #5
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I repeat.
Chainrings are not perfectly circular.
Going from 1/2in to 3/4in of play between the tight and loose spot is not uncommon.
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Old 11-22-05, 10:13 PM   #6
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Quote:
Originally Posted by teiaperigosa
how did you 'center' it ?
it sounds to me like your chainring bolts are too small for your chainring/crank holes...

I could prob leave my chainring bolts on my crank pretty loose and not have a problem, cause they hold the chainring to the crank like pins

edit:... either that, or I'm having a really hard time telling what you are talking about
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Old 11-22-05, 11:34 PM   #7
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ya i basically did the sheldon thing. i can get it so that there isn't any variation in the tightness of the chain. but somewhere when I'm riding I move the chainring around.

I just bought shorter bolts because the bolts I had before where too long. is there a lot of different bolts lengths? I told the guy I needed bolts for only one chainring. this lbs mostly sells to the local messengers and deals almost exclusively in track/fixed stuff so I'm pretty sure they gave me what I needed.

and I'm well aware that chainrings aren't perfect circles. 1980 shimano 600 cranks arent either im guessing but thats not the point. i got the thing working. i just can't keep it there.
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Old 11-23-05, 12:09 AM   #8
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Hopefully not too off topic, but anyone got a link to the Sheldon method for centering the chainring? I'm pretty sure mine needs it and didn't have much luck when I half-heartedly searched for it...
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Old 11-23-05, 12:28 AM   #9
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http://www.sheldonbrown.com/singlespeed.html
it's in the 'chain tension' section
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Old 11-23-05, 12:29 AM   #10
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i've noticed that my alloy chainring bolts will quickly loosen themselves as I'm riding unless I put a threadlocker on them. They creak like mad and the chain tension is all off unless I do this. I'm going to replace with steel as soon as i get a chance.
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Old 11-23-05, 12:30 AM   #11
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I went to a lbs and the guy told me to just get washers for the chainbolts meant for double chainrings. I got 'em, but I haven't tried yet. I have the 1/4" zinc washers from home of pot. If it works, it'll be cheaper (1.60 for 25washers) versus $5-$15.00 for single chainring bolts.
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Old 11-23-05, 12:49 AM   #12
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Hamandcheese,
It sounds like you have the right bolts.... they should be for single chainring, like these:

chainring bolts

Steel is a better choice than aluminum. Install them with the Sheldon Brown technique and use Blue Loctite.... you should be able to get it done before it sets up.

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Old 11-23-05, 01:15 AM   #13
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Quote:
Originally Posted by r-dub
http://www.sheldonbrown.com/singlespeed.html
it's in the 'chain tension' section
Thanks! I think I'm going to live with it till the weekend, then I'll try that...
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Old 11-23-05, 11:44 AM   #14
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I have always thought this would be a great place for improvement on track gear.

Why can't they make a crank/chainring combo that perfectly centers the CR? Is this that difficult to do or just not worth the effort?

Wouldn't it be nice not having to deal with tapping the chainring for half an hour to center it, and then it is still not centered no matter what you do.
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Old 11-23-05, 02:35 PM   #15
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The rear deraileur on a geared bike make up for the imperfect crank and chainring. So why would a manufacturer waste money making sure the crank and chain ring that are meant for a geared machine are circular and concentric?

I certainly hope that track specific cranks and rings are more circular and concentric, but you bet you will pay extra!

As for the CR bolts, go with steel, alloy will stretch and deform much more while under load and will therefore creep from the setting. bolt lengths meant for single or double bolts with spacers will give you pretty much the same results. But here is the paradox, if the bolt dia and CR hole dia have tight clearances, you keep your setting better, but you can't adjust the CR on the crank. If the clearance is larger, you get to make CR and crank adjustments, but you are more likely to creep from your setting.
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Old 11-23-05, 03:38 PM   #16
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I tried Sheldon's method with varied success. I just don't have the patience. Instead, I now do the following:
Find the tight spot in your chain and keep the crank in that spot, then loosen the rear wheel nuts and slide that sucker as far back as ya can. Then, loosen your chainring bolts a bit and spin the wheel. Once the chainring centers itself, retighten the c/ring bolts and re adjust your chain tension. Makes sense to me, but I am not a bike mechanic........so take my advice for what it's worth.
Or..simply get Campy cranks and chainrings, which are nice and round.
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