# Bent Chainring



## jfd986 (Jul 17, 2011)

The last thread about this died , so I figured I'd start a new one.


So I tightened all of the chainring bolts except one. I used a knife to tighten the bolts because the Icetoolz Chainring tool that I bought off the internet TOTALLY doesn't fit my chainring washers/nuts/whatever, grooves. So the knife worked fine for holding the nuts in place except for one, and now my chainring (both chainrings) are still wonky. 

Can one loose bolt actually do that much to the chainring? (Switch, I fixed the front derailleur by lowering it to the appropriate height. It shifts better now, actually gets the chain onto the big ring, will have to fine tune it a little, but now this lop-sided chainring is making the chain rub either one side of the derailleur or the other)

If the chainring is warped, what exactly do I have to do to fix it? Someone told me to "Get a wrench and clamp down and 'bend it back' " but I mean, when you start at one end with the wrench, and you're "bending", what's your point of reference ? How do you know if it's working, and how much exactly can you bend a chainring, all the way back to normal? Or "Just barely good enough" type deal?

Could there be a problem with the bottom bracket that's causing the lopsidedness ? I was wondering if it was that because both chainrings are swaying, not just the big ring.


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## cxwrench (Nov 9, 2004)

in the highly unlikely (let me repeat that...highly unlikely) event you have bent your bottom bracket spindle or a crank arm, you'd feel it at the pedal. you need to get all of the chainring bolts tightened before you do anything. yes, loose/missing bolts can result in the rings getting bent. 
when you try to straighten a chainring, you put the wrench on it and bend it a little. if that's not enough, bend it some more. no way to explain it better than that. you have to just give it a go. not sure what you mean by 'what is your point of reference?'. you look at the ring and the derailleur cage and you fix the part that's bent...should be easy to see.


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## PJ352 (Dec 5, 2007)

As was mentioned, you need to tighten all bolts before you can determine what's bent. If after all the bolts are tightened, both chainrings are swaying in unison, there's a possibility that one of the spiders is bent rather than the chainring(s).


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## jfd986 (Jul 17, 2011)

Cool. So then what type of spanner is supposed to work on an 80s Fuji road bike? Because the Icetoolz one didn't work at all, and a nailfile only barely worked on the others and one is still loose. I can only try the whole bending process after the final bolt is tightened (if that's the problem, then that's a quick fix) but what would the right tool be for that?


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## PJ352 (Dec 5, 2007)

A flat head screwdriver will work if the tip is wide enough.


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## davez26 (Nov 15, 2010)

One bolt loose can allow that ring to get pulled all over. 
A long flat headed screwdriver is good for ths, or in the case of an outer chainring, a crescent wrench can be of great use. Use the other ring as a guage or the deraileur. 
Like others have said, if one moves, one bent, both in tandem, bigger issues.


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## jfd986 (Jul 17, 2011)

I went to a hardware store and tried all the screwdrivers there. For some reason, none of them properly engage the groove in the chainring bolt. I'm going to take it to the LBS on Saturday and see if they have the knick-knack that'll solve it. Then I'll buy that. 

Significantly-worse-case scenario, one of the spiders connecting the crank arm to the chainring is bent. Now what, new chainring? New crank ?


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## PJ352 (Dec 5, 2007)

jfd986 said:


> I went to a hardware store and tried all the screwdrivers there. For some reason, none of them properly engage the groove in the chainring bolt. I'm going to take it to the LBS on Saturday and see if they have the knick-knack that'll solve it. Then I'll buy that.
> 
> Significantly-worse-case scenario, one of the spiders connecting the crank arm to the chainring is bent. Now what, new chainring? New crank ?


In that scenario, you could try straightening the arm. I've never done it, but others have with varying degrees of success. Next, probably the least expensive fix would be to find and replace just that part of the crankset, then straighten the chainring(s), if needed. The next cheapest option might be to find a 'like kind' of crankset, and the most expensive probably would be to replace the crankset and BB with a newer version.

Sometimes the most expensive option is the best option, but since you haven't yet tightened all the bolts, this (IMO) is jumping the gun a bit.


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## Mr Evil (Aug 12, 2011)

jfd986 said:


> I went to a hardware store and tried all the screwdrivers there. For some reason, none of them properly engage the groove in the chainring bolt...


Get a screwdriver or any similar tool that is wide enough, and attack it with a grinding wheel or file until it fits.


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## jfd986 (Jul 17, 2011)

Mr Evil said:


> Get a screwdriver or any similar tool that is wide enough, and attack it with a grinding wheel or file until it fits.


That quite literally just has to be done eh...I wasn't gonna do that because I was afraid of ruining the tool, but I guess if the bolt's gonna get tightened the choice is either buying a metal file and going over my biggest screwdriver, going online and buying another tool specifically for tightening the bolts and gambling that it's good enough then returning when it's not, or waiting until Saturday to go to my LBS and let them take a crack at it for $5 in labour, probably with a screwdriver that they filed down. Thanks Mr. E, I'm getting a file.


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## cxwrench (Nov 9, 2004)

this is the tool you need, Shimano TL-FC20 ,should be easy to find. if it doesn't work, something else is wrong...threads messed up, maybe?


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## Kerry Irons (Feb 25, 2002)

*The fix*



jfd986 said:


> I went to a hardware store and tried all the screwdrivers there. For some reason, none of them properly engage the groove in the chainring bolt. I'm going to take it to the LBS on Saturday and see if they have the knick-knack that'll solve it. Then I'll buy that.
> 
> Significantly-worse-case scenario, one of the spiders connecting the crank arm to the chainring is bent. Now what, new chainring? New crank ?


As others note, you need to have the chain ring bolts tight before drawing conclusions. Often you can just hold one side of the nut with a small bladed screwdriver enough to tighten the bolt. Be sure the threads and all the metal-to-metal contact surfaces are greased.

This wobble is likely either a slightly off spider arm, or a slightly off chain ring. Either/both is a very common thing (I won't say problem, because in most cases, it has no effect on performance).

Assuming that your BB is OK (i.e. not loose - it's extremely unlikely that it's bent), you have to straighten your spiders and/or chain rings. If it's a CF crank, then only your chain rings can be straightened. Hold a small screwdriver or other short, pointed object against the seat tube so that the tip just grazes the crank spiders as they pass. If the spiders are bent, you can even them out as follows:

Place the bike on its side with the crank supported on a block of wood at the axle. With another block of wood or a stout dowel placed at the end of the offending spider(s) give it a whack with a hammer. Check for change in alignment. If you got no change, hit it harder next time. Repeat until all the spiders are even. You may need to bend them away from the frame (brace the right crank on the block of wood) or toward the frame (brace the left crank).

Once the spiders are even, check the chain rings with the same technique except put the point of your screwdriver at the teeth of the rings (most likely the big ring only if the spiders are even). Straighten the chain ring by placing a large adjustable wrench over the ring with the jaws adjusted for a slip fit over the ring. Bend gently, and check alignment. Repeat until you've got it right.

Even with the chain rings dead straight, you still will get some deflection due to pedaling forces, but that should greatly improve your situation.


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## jfd986 (Jul 17, 2011)

As it turns out, the one chainring bolt wasn't tightening not because I didn't have the right tool, but because the threads on the bolt itself are toast. It gets halfway in and then just stops there, refuses to tighten further.

Was gonna order these since it's a double chainring:

Amazon.com: Sugino Double chainring bolt/nut set, M8x8.4 10/pcs: Sports & Outdoors

Is this the right move here? Or is there another way to replace a threadless bolt ?


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## Mr Evil (Aug 12, 2011)

If you get new bolts, try to get ones that take an Allen key on both sides. They're much more convenient than the traditional ones with a slot on the back.


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## PJ352 (Dec 5, 2007)

Before shelling out ~$14 + shipping, consider taking the bolt/ nut to your LBS. They might have some spares lying around....


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