I sheared off the crank arm bolt
10-27-12, 04:50 PM
#1
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I sheared off the crank arm bolt
I have an older FSA SLK crankset, and the bolt has always been a problem. No matter how hard I try it just wouldn't stay tight. Well today on my way home from a fifty mile ride it had come loose for the second time today, and I had tightened it before I left too. This time though when I tightened it it suddenly started turning free, but what had actually happened was that the flange sheared off, making the bolt useless. I took the long silver sag wagon the rest of the way home.
My question is whether I did any damage beyond the bolt? I already ordered a new bolt and extractor set from FSA but will I still have problems?
My question is whether I did any damage beyond the bolt? I already ordered a new bolt and extractor set from FSA but will I still have problems?
10-27-12, 05:12 PM
#2
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I'd say no to the other damage. Essentially what has probably been happening is the flange has been cracked or yielded for some time and that could explain why it was coming loose continually. Also you could try blue loctite.
10-27-12, 07:13 PM
#3
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What torque are you tightening the bolt to? I believe the spec is 40nm +-. I suppose Loctite might help, but the assembly instructions don't call for its use.
10-27-12, 08:33 PM
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Is this an older 'square taper' crank? check the taper hole on the arm it maybe rounding out, cranks that repeatedlt come loose is sure sign cause of the hole rounding out.
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“One morning you wake up, the girl is gone, the bikes are gone, all that's left behind is a pair of old tires and a tube of tubular glue, all squeezed out"
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10-27-12, 08:33 PM
#5
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Unfortunately I don't carry a torque wrench with me on the road, but the bolt does have the recommended torque on it, 350-500 kgf cm (which I guess is 35-50nm, so yes 40+-). I do have a torque wrench but I never used it, in fact I think I bought it when first assembling this bike. I'll learn how to use it once the new bolt comes. With a hurricane bearing down on us, and then my travel to Memphis, I won't need the bike this week anyway, and besides, that's what the 3 other bikes are for.
The manual also says to not flatten the wave washer, but I don't know how I would know I'm doing that.
The manual also says to not flatten the wave washer, but I don't know how I would know I'm doing that.
Last edited by zacster; 10-27-12 at 08:43 PM.
10-27-12, 08:35 PM
#6
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And the rounding makes the crank come loose, which causes the rounding, and so on...
10-28-12, 12:06 AM
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Unfortunately the single bolt design is very poor design. To work properly the wavy washer needs to be semi- compressed to hold the bolt tight. If you have overtightened the bolt then the washer probably has been over compressed and can't do it's job any more. Further, the design requires a pretty tight fit on the splines. If it was come loose and rattled around at all the arm is probably toast.
Edit: you might want to see if you can purchase an updated FSA left crank arm. I don't know if it will fit (it should) but it has a clamp style that pretty much guarantees it will not come loose.
Edit: you might want to see if you can purchase an updated FSA left crank arm. I don't know if it will fit (it should) but it has a clamp style that pretty much guarantees it will not come loose.
Last edited by onespeedbiker; 10-28-12 at 10:59 AM.
10-28-12, 10:10 AM
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No, not a square taper. This is a mega-exo 2 piece crank, a more modern design. I vaguely recall the spindle being splined to take the left arm, and permanently attached to the right arm.
And the rounding makes the crank come loose, which causes the rounding, and so on...
And the rounding makes the crank come loose, which causes the rounding, and so on...
Oh OK that is way to new for me.
__________________
“One morning you wake up, the girl is gone, the bikes are gone, all that's left behind is a pair of old tires and a tube of tubular glue, all squeezed out"
Sugar "Kane" Kowalczyk
“One morning you wake up, the girl is gone, the bikes are gone, all that's left behind is a pair of old tires and a tube of tubular glue, all squeezed out"
Sugar "Kane" Kowalczyk
10-29-12, 08:32 AM
#11
Senior Member
I have an older FSA SLK crankset, and the bolt has always been a problem. No matter how hard I try it just wouldn't stay tight. Well today on my way home from a fifty mile ride it had come loose for the second time today, and I had tightened it before I left too. This time though when I tightened it it suddenly started turning free, but what had actually happened was that the flange sheared off, making the bolt useless. I took the long silver sag wagon the rest of the way home. My question is whether I did any damage beyond the bolt? I already ordered a new bolt and extractor set from FSA but will I still have problems?
