# My crankarm is brushing against the chain...



## semaj (Aug 30, 2007)

...is this considered out of the ordinary? My other road bike with Campy 10s cranks have about a 2mm clearance when in the same gear combination, but the Lightning cranks have no room at all.


















Do you guys think this could be a manufacturing error as the crankarms seem to be moulded by hand.


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## frdfandc (Nov 27, 2007)

That is definitely a bad thing. Nothing should be rubbing the crank. I'd call the manufacturer and send them those pictures.

But on 2nd thought, what chainrings are you using? And are they installed correctly?


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## semaj (Aug 30, 2007)

frdfandc said:


> That is definitely a bad thing. Nothing should be rubbing the crank. I'd call the manufacturer and send them those pictures.
> 
> But on 2nd thought, what chainrings are you using? And are they installed correctly?


The chainrings are Stronglight CT2. To my knowledge they were installed correctly. I'm guessing it's a manufacturing issue as the spindle on that crankset was 1mm to short and I had to send that in to get it fixed after destroying two sets of BB30 bearings due the short spindle. I'm guessing I got to send this in again to get this new issue fixed.

To be frank, I'm not too happy with this situation.


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## rx-79g (Sep 14, 2010)

It seems likely to be the crank and/or spindle, but it would be instructive to know what's going on. Read Sheldon Brown's article on chainline and measure that, seeing if it is a crank location problem (like spindle length) or if the arm is off compared to the rings (a defect in the crank itself).

Other less likely problems could be frame rear end alignment, which would require an out of dish wheel to look right, or a BB shell which is not square to the rest of the frame, where the BB spindle is tilted toward the rear wheel on the drive side. 

While some of these seem less likely at first glance, if it was purely the crank arm I would doubt the arm would be able to clear the FD. The fact that it can clear the FD yet strike the chain makes more of a case for a chainline or alignment problem that is putting the chain at a greater angle than it should.


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## bikerjulio (Jan 19, 2010)

on their website saw this:



> Removable, interchangeable aluminum spyders
> Compatible with Quarq CinQo power spider (www.quarq.us/Spiders/CinQo.html)
> and Specialized spyders.
> Available Lightning Spyder sizes: 110, 130, and 94 MTB double;
> ...


perhaps spider wrong or wrongly assembled?


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## Dave Hickey (Jan 27, 2002)

If the chain is rubbing the arm, it has to be the distance between the outer ring and the arm is too short.... Chainline and spindle length won't affect chain rub on the arm...

1. The spyder was installed wrong
2. The rings were installed wrong

Check with the manufacturer


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## Dave Hickey (Jan 27, 2002)

bikerjulio said:


> on their website saw this:
> 
> 
> 
> perhaps spider wrong or wrongly assembled?



I just noticed you beat my too it...that is my guess too...Spider


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## rx-79g (Sep 14, 2010)

Dave Hickey said:


> If the chain is rubbing the arm, it has to be the distance between the outer ring and the arm is too short.... *Chainline and spindle length won't affect chain rub on the arm*...
> 
> 1. The spyder was installed wrong
> 2. The rings were installed wrong


Sure it can, Dave. If the chainline is bad (too short spindle) the chain will come off the crank with enough additional angle to hit the arm.

If it was just the arm itself, it would be hard for the FD to not be rubbing as well.


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## Dave Hickey (Jan 27, 2002)

rx-79g said:


> Sure it can, Dave. If the chainline is bad (too short spindle) the chain will come off the crank with enough additional angle to hit the arm.
> 
> If it was just the arm itself, it would be hard for the FD to not be rubbing as well.



I guess it's possible but that would have to be one seriously short spindle

I just threw one of my bikes on the work stand( big ring, small cog)... In order to get the chain to rub the arm, the drive side spindle would have to be 5mm too short. I guess it's possible


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## rx-79g (Sep 14, 2010)

Dave Hickey said:


> I guess it's possible but that would have to be one seriously short spindle
> 
> I just threw one of my bikes on the work stand( big ring, small cog)... In order to get the chain to rub the arm, the drive side spindle would have to be 5mm too short. If that was the case, the inner ring would hit the chainstay... I guess it's possible


I don't know what the problem is - I also mentioned a cocked BB shell would also do it. I have about 5mm as well, but that's with 170 crank arms. Increase the angle and have longer arms and you'll eat the space up.


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## cxwrench (Nov 9, 2004)

gotta be something like you're thinking...if it was just the spider wouldn't the crank arm be hitting the front derailleur like you mentioned?


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## bikerjulio (Jan 19, 2010)

Dave Hickey said:


> I guess it's possible but that would have to be one seriously short spindle
> 
> I just threw one of my bikes on the work stand( big ring, small cog)... In order to get the chain to rub the arm, the drive side spindle would have to be 5mm too short. I guess it's possible


If the spindle is too short you might notice a lack of clearance from the chainstay to the inner ring on one photo - there's lots of clearance


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## FBinNY (Jan 24, 2009)

Curious, how does the crank arm touch the chain yet clear the frond derailleur cage which is outboard of the chain?

The fact that it does makes me think of three likely possibilities, none of which are good signs.

1- crank is bent or warped so the tip is inboard of the middle
2- rear triangle is offset toward the right, bringing the chain out too far when in high gear.
3- BB shell is not truly square to the frames centerline, so the crank is more in at the back than the front.

Pin down the cause tighter, by laying an 18" straightedge on a secant against the outer chainring and carry the line back to the cassette to see where it lines up. Also eyeball the crank arm for straightness.


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## rx-79g (Sep 14, 2010)

Looking over the installation instructions, I can see a number of points that could go wrong. Reversible spiders, BB spacers for 68mm shells, etc. It seem just as likely that something is put together wrong as an actual defect.
http://www.lightningbikes.com/LIGHTNING CARBON CRANKS INSTALLATION PROCEDURE 6.pdf

I suggest using a ruler and the frame tube centerline to check both chainline AND the Q factor of both crank arms. Uneven Q spacing would indicated a BB installation problem (whole crank slid to the left), and even Q with small chainline would indicate improper spider installation. Again, I don't know what's going on here, but here's two things to rule out without taking anything apart.


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## bikerjulio (Jan 19, 2010)

Just look at the distance from the chainstay to the inner ring in the 2nd photo.

This has to be a spider issue.


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## FBinNY (Jan 24, 2009)

bikerjulio said:


> Just look at the distance from the chainstay to the inner ring in the 2nd photo.
> 
> This has to be a spider issue.


I doubt it. The tip of the crank arm touches the chain, yet the arm clears the FD cage which is of necessety outboard of the chain. That means the crank arm and chainline are angled toward each other in the back. Either the arm is bent, the entire BB isn't square to the frame plane, the rear triangle is offset to the right (or the crank too far to the left) causing the chain to come forward from the outside more than the typical10-15mm that happens in high gear.

The photo that would be most revealing is one shot from directly above, lined up with the chainring and with the crank just below where it brushes the chain. But you can make a quick sketch showing the angles needed for the chain to move from about 1/4" inboard of the arm at the half way point to touching the arm at the tip.

A quick diagnostic for the OP, lay a straightedge on a secant against the chainring face and see if the arm is parallel, or bent inboard at the end.


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## AJL (Jul 9, 2009)

> I may have missed something here, but does this happen only with one arm or both?


OMG, I don't believe I said that :blush2: 

What I was trying to figure out was if there was a manufacturing defect in the layup of the crank by comparing it to the other...nvm. Just do what FBinNY suggested.


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## olr1 (Apr 2, 2005)

Crank looks bent to me.


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## rx-79g (Sep 14, 2010)

AJL said:


> Good point. The crank-arm does seem to be a bit bulbous at the pedal end.
> 
> I may have missed something here, but does this happen only with one arm or both?


Yes, you've missed something. The left side arm does not touch the left side chain.


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## RJP Diver (Jul 2, 2010)

AJL said:


> I may have missed something here, but does this happen only with one arm or both?


If the LEFT crank arm is hitting the chain... something is _*REALLY*_ out of whack!

:aureola:


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## FBinNY (Jan 24, 2009)

AJL said:


> Good point. The crank-arm does seem to be a bit bulbous at the pedal end.
> 
> I may have missed something here, but does this happen only with one arm or both?


Forget about the left side, and don't worry about the shape of the crank arm, except to see if it's bent inward toward the chainring.

You are missing something. 

*To see it, draw a sketch* showing the chainring, crank, FD and chain looking down from the top. 

You'll see that the chain comes in on an angle from outside of the line of the chainring when on the smaller rear sprockets. In order to keep Q factors to a minimum, crank arms are kept close and low clearance when the chain comes from the outermost rear sprocket is normal.

The fact that it touches the arm means the crank's tip is in more than it should be, or the angle is too great, because the crank is too far in, or the cassette too far out.

So you have three possibilities, and with some careful measurements and maybe comparisons to other bikes you'll pin down the problem and know how to fix it.


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## rx-79g (Sep 14, 2010)

Let's keep in mind here that the crank arm doesn't just have to clear the chain, but on most racing bikes it runs pretty close to the chainstay as well. If the problem is the arm angle or position, the arm would be just about brushing the chainstay on the right side. So that's something else to put an eyeball on.


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## AJL (Jul 9, 2009)

Weird, I just posted, but it says the post was 3 hours ago, and that I just edited it?! I guess I need to suspend my experiments in time travel


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## FBinNY (Jan 24, 2009)

AJL said:


> Weird, I just posted, but it says the post was 3 hours ago, and that I just edited it?! I guess I need to suspend my experiments in time travel


Is it possible that you're in the East and the forum clock is in the pacific time zone?


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## AJL (Jul 9, 2009)

FBinNY said:


> Is it possible that you're in the East and the forum clock is in the pacific time zone?


Yes, but I have my timezone set correctly in my account so this usually doesn't happen - a ghost in the machine for a few moments I suppose.


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## kbwh (May 28, 2010)

I suggest the OP to put on cranks of the same make as he has on the other bike.


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