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PostPosted: Wed Mar 21, 2012 7:51 am 
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Joined: Wed Dec 07, 2011 1:26 am
Posts: 414
Location: California's country side
I just installed a new SRAM Red crank and found the small chain ring not running as straight as I like, I can see the chain move in and out a little.
I think this happens in my cranks to some degree? But doesn't seem as noticable back then.
Do they have some ramping to them the cassette does?

It's only noticable in the small chain ring.
2 minor issues
- setting the FD low limit is a bit looser to clear the part that rubs.
- in the small chainring and the smallest 2 cogs in the back the chain rubs the LARGE chainring. Even though the derailleur cage is trimmed out of the way. But I think maybe this bike has shorter chainstays too and doesn't help.

Has anyone seen this before and is there a way to fix?


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Posted: Wed Mar 21, 2012 7:51 am 


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PostPosted: Wed Mar 21, 2012 5:23 pm 
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Joined: Sat Jul 29, 2006 2:36 am
Posts: 1184
Location: UK
I don't know about ramps but sometimes chainsets don't run 100% true but will function fine.
Have you checked the chainring bolts and stripped it to see if anything is untoward?

Re. chainline, ignore the small / small combo as that shouldn't be used.
Make sure the chain is under tension when you check the small / 2nd combo.
If it still rubs check the chainset is centred correctly. If all seems well it's just something you're going to have to accept.


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PostPosted: Wed Mar 21, 2012 6:07 pm 
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Joined: Wed Dec 07, 2011 1:26 am
Posts: 414
Location: California's country side
5 8 5 wrote:
I don't know about ramps but sometimes chainsets don't run 100% true but will function fine.
Have you checked the chainring bolts and stripped it to see if anything is untoward?

Re. chainline, ignore the small / small combo as that shouldn't be used.
Make sure the chain is under tension when you check the small / 2nd combo.
If it still rubs check the chainset is centred correctly. If all seems well it's just something you're going to have to accept.


I visually checked the spider and everything is on without gaps, but didn't mess with the chainring bolts

I did have to add 1.5mm of spacer on the NDS for this crankset + frame combination (BB30), normally I get away with .5mm spacer.
I was wondering if the driveside is too far inwards, but I have never heard of adding spacers on the drive side.

I backed the B tension screw out enough to set the smallest cog clearance, but yes it could be on the loose side.
Anyway, I do not use the small + 2nd smalles cog either so it doesn't really matter to me.


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PostPosted: Fri Mar 30, 2012 7:13 pm 
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Joined: Fri Mar 30, 2012 6:43 pm
Posts: 2
I have the same problem (the chain starts to rub the 53 while on the 39 in the front when I shift to the two smallest cogs - T13, T12). I can ride in the low-low combo, but its not seamless as it used to be.

This all started after rebuilding up on a new 54cm frame (came down from a 55cm). I'm running an older Shimano 6500 series 9x2 gear setup (everything except the cassette and chain). The cassette is a SRAM 950, T12-T26, and the chain, WAS a KMC.

During the rebuild I kept all the original components - except for the chain which needed to be replace - I replaced it with a DA 7801 which I had stock piled.

I'm suspecting the chain as a culprit since it appears to contain links not as well machined or "rounded" as on the KMC.

If its not that, then its probably differences in the frame that cause the Crankset to be closer to the BB on the drive side. I won't know for sure since I didn't measure the old build.

I'm hoping its the chain, which I'll eventually replace. Until then I'll just have to avoid the affected gear combinations. The only one I'll really miss is the T13/39 which I used rather often.


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PostPosted: Sat Mar 31, 2012 4:26 am 
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Joined: Fri Mar 30, 2012 6:43 pm
Posts: 2
I compared the chains again side-by-side and was completely off. It turns out the DA is ever so slightly narrower then the KMC (I should have expected this considering its a 10 speed chain replacing a 9).

Still searching for alternatives, I took off the cassette hoping to find a spacer/shim; no luck. If I had one, removing it might have done the trick.

Next I'm going to see if I can find a thin shim/washer to put in between the frame and the drive-side of the BB bearings.


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