Crank arm fatigue

Tamir

Speeding Up
Aug 19, 2011
56
0
26
35
Tokyo
www.facebook.com
#1
Recently I've noticed that one of my pedals has been feeling loose. When I went to tighten the bolt that attaches it to the crank arm, I found that no matter how much I tightened the bolt, there was still too much play in the pedal. It looks like the hole in the crank arm which the pedal attaches into is now too big and there seem to be small hairline cracks running from the hole. It's a carbon fiber crank arm (FSA Octalink, carbon fiber) so I imagine that the CF has become fatigued (if that's possible) and the crank arm need to be replaced.

I currently have a 9 speed Dura Ace groupset. I'd prefer to avoid up/downgrading the whole groupset to 10 speed (probably Tiagra due to budget limitations). From looking around, it seems that using a "10-speed" crankset with a 9-speed cassette is okay, and using a 9-speed chain is also okay.

Any opinions or comments?
 

kpykc

Speeding Up
Jun 13, 2007
804
4
38
39
Tokyo
#2
Did you check your pedals themselves? - They tend to develop a small play after a long use especially in the rain, bearings could be loose or rusty. You might have to clean, re-grease or re-tighten them.

I think there is no cure for cracked cranks - keep using them (at your own risk) or buy new ones.

BTW, pictures might help. I am not a carbon specialist, but some people here have knowledge and experience to comment on that.
 

Gunjira

Maximum Pace
Oct 2, 2009
1,003
176
83
Tokyo
#5
While I suspect the real culprit to be the pedal as well, if there is a chance you damaged the crank in the process I wouldn't recommend riding.
Did you try out some other pedals? If the problem persists in that case, change the crank ASAP.

I broke a crankarm before and because this usually happens under load, it is very dangerous.
 
Sep 2, 2009
5
0
0
#6
Yeah, having snapped cranks catastrophically before, I seriously recommend you don't ride them until you get them properly checked.
 

AlanW

Maximum Pace
Jan 30, 2007
1,214
436
103
Tokyo
#7
I had an FSA crank fail exactly the way you describe. The pedals screwed into aluminium inserts that were bonded to the carbon. The bond failed and the pedals were loose.
Any 10 speed crank will work with 9 speed no problem.
 

Tamir

Speeding Up
Aug 19, 2011
56
0
26
35
Tokyo
www.facebook.com
#8
Thanks for your warnings, guys.
I'm aware of the dangers and will get new cranks asap.

The attached pics show the play in the pedal-crank interface as well as possible cracking. Sorry for the low resolution (iphone pics).
 

FarEast

Maximum Pace
May 25, 2009
5,528
538
193
Yokohama
#9
Yep thats come away - exactly as Alan said. Iwould stop riding on it immediately the likelihood of that coming away completely is very high and you'll it will put you in the road.
 
Sep 2, 2009
5
0
0
#11
Yikes. One hard push on that could pull that right out, and leave you in a whole world of pain and injury, or worse.

The stuff of nightmares!
 

andywood

Maximum Pace
Apr 8, 2008
1,719
1,366
133
Niigata
#12
I had an FSA crank fail exactly the way you describe. The pedals screwed into aluminium inserts that were bonded to the carbon. The bond failed and the pedals were loose.
Any 10 speed crank will work with 9 speed no problem.
I had exactly the same thing. I've posted on here before about it but I find FSA to be terrible quality. The bottom brackets are very poor.

I'd choose Shimano for durability and customer service.

Andy

www.jyonnobitime.com/time
 

Tamir

Speeding Up
Aug 19, 2011
56
0
26
35
Tokyo
www.facebook.com
#14
Thanks for the advice, guys.
I'm happy to report that I've had no serious accidents due to this problem.
I had an old set of Shimano cranks that I managed to get on (with some trouble due to my own ineptitude and the need to move the front derailleur around, etc.) as a temporary fix. Will be ordering/buying new cranks and maybe BB soon.