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Discussion Starter · #1 ·
My big chainring on FSA SLA compact crank is wobbling and rubbing on the inside of the
derailer. I heard that the ring could be trued. DOes any one knows haw to true the chainring ? Should I use a hammer, vice...? Any suggestions. Thank you.:confused:
 

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NeoRetroGrouch
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Ab24029 said:
My big chainring on FSA SLA compact crank is wobbling and rubbing on the inside of the
derailer. I heard that the ring could be trued. DOes any one knows haw to true the chainring ? Should I use a hammer, vice...? Any suggestions. Thank you.:confused:
Assuming that it is just the chainring, use a small (~6") adjustable wrench (Cresent wrench) to gently bend the ring. - TF
 

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For fine truing once youv'e got close with the adjustable wrench, try a small soft headed hammer. Works great!
 

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Resident Curmudgeon
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Like TurboTurtle said, make sure it's really just the chainring. It could be the bottom bracket flexing, a bent crank arm, or a bent BB axle. I'd check those 1st, then proceed to the chainring.
 

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I've also used the gentle application of a long, flat bladed screwdriver wedged against the spider or BB, with the shaft pressing against the chainring.
 

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A plastic mallet works well. I've had bad luck with an adjustable wrench, that's more for mountain bike impacts, in my experience. If you must use an adjustable wrench, focus on the "spokes" of the ring rather than the ring itself.

You'll never get it perfect, if perfection is desired, buy a new ring, assuming your cranks are straight.
 

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Discussion Starter · #8 ·
Thank you. The bottom bracket is new and the frame is new. The crank is slightly used that I bought on e-bay. I do not think it is the BB or brame. I think it is the big chain ring. I tried to use the wrench without removing the ring from the bike-no good. I guess I should take it off the bike and try a little hammer. Right ?
 

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Ab24029 said:
Thank you. The bottom bracket is new and the frame is new. The crank is slightly used that I bought on e-bay. I do not think it is the BB or brame. I think it is the big chain ring. I tried to use the wrench without removing the ring from the bike-no good. I guess I should take it off the bike and try a little hammer. Right ?
Tap the ring with the hammer while it's still installed on the bike, it's the only way to check your work and know if you're actually making progress.

Seriously though, if it's a minor wobble, you're not going to get it much better, maybe only worse.
 

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If both chainrings have runout, then it's not the rings but the interface on the crank or BB or the BB itself.

If it's related to one of these, you may also try rotating the position of the crank on the bb and see if it's any better. It only takes a very small amount of error on the interface to end up with quite a bit of runout at the outside of the large ring.

You may want to also take the chainring off and see if it's flat on a quality surface (preferrable a granite surface plate). There could also be an issue where the rings attach to the spider. Check to make sure the ring is completed seated against the spider. Mark the high spot with a pencil and rotate the ring on the spider to see if it moves with it. This isn't a fix since most cranks have a pin in one position but a way to get to root cause.

You may also just consider returning the crank before you bang on it since it's new.
 

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Most likely crank spiders

bg. said:
A plastic mallet works well. I've had bad luck with an adjustable wrench, that's more for mountain bike impacts, in my experience. If you must use an adjustable wrench, focus on the "spokes" of the ring rather than the ring itself.

You'll never get it perfect, if perfection is desired, buy a new ring, assuming your cranks are straight.
The problem with using a mallet is that the force of the impact is taken directly by the bearings. Here is how to deal with this:

Assuming that your BB is OK (i.e. not loose - it's extremely unlikely that it's bent), you have to straighten your chain rings. 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 (most likely problem), 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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