Inner chainring grinding chainstay?

[phcollard]

Hi folks,

So I am building a new bike and I started with the BB. I assembled the crankset on the DS and next thing I know the inner chainring is rubbing against the chainstay. Muh.

This is an Octalink BB with corresponding crankset and the inner ring is already the smallest I can get (48T).

What's the solution to this? Is there one such thing as BB spacers? How much mm in clearance is needed?

Thanks a lot for your help.

Philippe.

[gdw]

What model frame, crankset, and bottom bracket are you working with?

[miguel]

is the frame straight?

[phcollard]

What model frame, crankset, and bottom bracket are you working with?

It's this frame (http://forums.thepaceline.net/showthread.php?t=94942).

BB is a Shimano Octalink BB-5500 (English thread).
Crankset is a Shimano Ultegra 6500 with TA chainrings 48/38.

[Mark McM]

Hmmm... Something funny is going on here.

In answer to your question, yes, there are bottom bracket spacers available that can be fitted under the (right) fixed cup, which can shift the BB/crank/chainrings outward. BUT ...

You are using a very standard combination of BB/cranks, which should produce a standard chainline, and you are using a slightly smaller than standard inner ring (38), so a properly designed frame should provide adequate chainring clearance.

I'd take the advice of looking something that is out alignment. Could the rear triangle/chainstays been bent to the right? Could the chainstay have gotten damaged/distorted?

Also, it would probably behoove you to find out if the BB/crank really is aligned to the correct offset. Here's a good article by Sheldon Brown about chainline measurement and alignment (http://www.sheldonbrown.com/chainline.html)

[phcollard]

To my untrained eye the frame looks properly aligned. The rear wheel is perfectly centered at the brake bridge and between the stays. I know it should be properly measured by a framebuilder but I'm thinking it would have to be so way off if it was an alignment issue that everything would be out of whack.

And I trust the seller as well. I'm sure he would have told me. And the box was not damaged. So I'm confused :confused:

I measured the chainline as it was and it's up to Sheldon's standards.

I have found a 2.5mm spacer from a SRAM bottom bracket. It's not a perfect fit but now the chainring is at 2.5mm of the chainstay.

Sounds good enough?? I don't know. I'll have the frame checked by a framebuilder but I assume I can ride it with this temporary solution in the meantime??

[gdw]

Is the crankset a triple without the small ring?

[phcollard]

No it's a double...

Double confused.

[Richard]

is the inner ring on backwards or inside out?

[phcollard]

is the inner ring on backwards or inside out?

Here's a pic of the current situation... thanks for your help folks!

http://dl.dropbox.com/u/3032014/cranks.JPG

[miguel]

take to LBS
ask for frame alignment guage
check

[gdw]

I hope the spacer solves your problem. That's a really pretty frame.

[Fixed]

I hope the spacer solves your problem. That's a really pretty frame.
+1
cheers

[phcollard]

I hope the spacer solves your problem. That's a really pretty frame.

Thanks a lot!

I double checked with the string between dropouts and headtube and it looks like the frame is dead straight.

The spacer works. There is now about 3mm between the chainring and chainstay.

My chainline is off by 1mm only. But now my DS crankarm is 5mm further to the right and my NDS crankarm is 5mm closer to the left.

Last questions and then I'll pay you a drink :D

- Is a clearance of 3mm enough?
- Is it gonna be annoying to have the crankarms slightly off?

[palincss]

It worked when Douglas had it, didn't it? That argues for something off with the crank/bottom bracket installation rather than the frame.

[phcollard]

It worked when Douglas had it, didn't it? That argues for something off with the crank/bottom bracket installation rather than the frame.

Yes I'm guessing it was working for the previous owners.

I have tried two cranks/BB... all Shimano Octalink... 105, Ultegra, Dura Ace and it's all the same thing.

I've got the same combo on the girlfriend's bike and previously that what I had on my Serotta. Zero issue.

[gdw]

3mm should be ok since chainsuck isn't an issue with road bikes. You probably won't notice the 5mm move to the right either.

[Peter P.]

Measure your BB width to verify it's actually 68mm wide. Maybe you actually NEEDED the spacer to bring everything into spec.

The fact you claim you measured you're currently 1mm off the standard chainline tells me that should you encounter any front shifting difficulties, suspect this 1mm to be the source.

Today's shifting systems are more particular about things like chainring position and how the front derailleur cage integrates with the less than optimum position.

[phcollard]

Measure your BB width to verify it's actually 68mm wide. Maybe you actually NEEDED the spacer to bring everything into spec.


Good call I did not think about this one. I just checked and the BB shell width is exactly 68mm.

What a mystery!

[victoryfactory]

wait a second.
Aren't there two or three different spindle lengths
available on octalink BB's?
Maybe you have a 109.5 and you need the 116?
Would this solve the problem?

VF

[phcollard]

wait a second.
Aren't there two or three different spindle lengths
available on octalink BB's?
Maybe you have a 109.5 and you need the 116?
Would this solve the problem?

VF

Good call as well!

The current BB is an Octalink V1.

http://www.sheldonbrown.com/bbsize.html#shimano

I think they only come in 68/109.5

I can see on the bay several cheap V2 with more length but are these compatible with my cranks?

[gdw]

They, v1 bb's, also come in 112.5 (XTR M952) and 118.5mm. The XTR was for a 73mm shell but came with a spacer for 68mm shells. I bet the chainstays on your bike have a rounder profile than other designs and there wouldn't be a problem if the driveside stay had been crimped near the rings.

[phcollard]

They, v1 bb's, also come in 112.5 (XTR M952) and 118.5mm. The XTR was for a 73mm shell but came with a spacer for 68mm shells. I bet the chainstays on your bike have a rounder profile than other designs and there wouldn't be a problem if the driveside stay had been crimped near the rings.

Hey thanks I'm gonna look for one of those. Thanks a lot.

You're absolutely right: the chainstays are very round and no crimp.

Now beer for everyone! :beer:

[old_fat_and_slow]

I'm no expert on Octalink BB, since I'm a Campy guy, but if the longer spindle idea doesn't pan out, check to see if there are square taper spindles available to resolve the issue with a corresponding set of square taper cranks.

I know that probably more jack to resolve the issue than you wanted, but if all else fails you may have to look into that.

[phcollard]

I'm no expert on Octalink BB, since I'm a Campy guy, but if the longer spindle idea doesn't pan out, check to see if there are square taper spindles available to resolve the issue with a corresponding set of square taper cranks.

I know that probably more jack to resolve the issue than you wanted, but if all else fails you may have to look into that.

Thanks I'll look into that if I cannot find an XTR BB (looks like it's impossible).

More jack? I'm so anal about my bikes that I'll do anything to get things right :D

[victoryfactory]

It's possible that your frame was built to accommodate
slightly wider tires than the usual 23-25mm too
That would call for a longer BB spindle to clear the chain
stays.

I would say try it with the shim first. It might be fine.

Good luck

VF

[Lifelover]

I recall a similar thread to this and the final answer was to have the frame crimped a bit.

Don't recall how it was done but I'm pretty sure it did not even mess up the paint.

I would contact the builder directly or maybe PM one of the builders here or across the hall.