# FSA crank keeps coming loose



## STLRoady (Mar 29, 2006)

Any help with the follow is greatly appreciated.

Built a new bike a few weeks ago and the Full Speed Ahead SL-K Compact MegaExo keeps coming loose. I notice the pedals start to wobble and when I get home I torque it down to 450 in/lbs per FSA's installation guide. Despite this in about 60-100 miles it comes loose again. The only thing I can think of to try is some locktite.

Thoughts?


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## skepticman (Dec 25, 2005)

If you clean the threads, put some Loctite on, torque it to spec and let it sit overnight without riding it while it cures, it should stay tight. If not, then try talking directly to FSA.


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## sabrops (Sep 25, 2005)

My thought is that FSA cranks suck. I can hardly tell you how much I wish I had bought Dura Ace instead of K-Force.


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## VaughnA (Jun 3, 2003)

I've had no problems with mine. But if the BB shell isn't faced and absolutely parallel I've heard it can come loose with the external cups. Did you get the BB faced before assembly?


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## JimP (Dec 18, 2001)

There seems to be a little slop in the fit of the spline between the left crank arm and the bottom bracket. The fixing bolt doesn't come loose but the left crank arm does have a little rotational movement after a while. I have emailed my issue to FSA a couple of days ago but haven't received an acknowledgement yet. I will post FSA's response, if I ever receive one.


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## bikeboy389 (May 4, 2004)

My understanding (you should probably do a search here on this) is that once a splined crank comes loose and gets some use on it--like would happen if it loosened during a ride and you needed to get home--the splines (either on the crank or BB or both) are kind of farked, and it will never go together properly after.

I don't know if this is true, but I've seen it mentioned around here before.


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## b987654 (Aug 18, 2005)

is the bb shell cracked or are the threads damaged ? i hope not, but it hasn't been mentioned yet.


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## ericm979 (Jun 26, 2005)

It's hosed. I've heard of a lot of SLK cranks having this. Once they come loose they are gone. Mine are still with FSA for a possible warranty replacement. The shop sent them in around july 1st. I bought a replacement set of cranks rather than wait, and I have not been pressuring the shop or FSA to send my warranty replacement cranks back.


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## STLRoady (Mar 29, 2006)

*Locktite saved the day.*

I cleaned the threads, put on some locktite and waited 24 hours. After about 90 miles they are still solid as a rock. I'll post another update if they come loose again.

Thanks!


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## nwfanatic (Feb 5, 2005)

Loctite did the trick for me too. I have 1500 miles on the FSA SRM crankset w/ no loosening problems....


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## JimP (Dec 18, 2001)

My issue is either an engineering design or manufacturing defect. FSA has designed the straight cut splines to have a little play in them. This slop was there on day one. Other designs have a slight taper in the splines that prevent this kind of movement. The blue outer seal presses between the bearing and the crank arm which is supposed to keep the crank arm from moving. The blue rubber like substance doesn't completely stop the movement and thus wears and comes out. The crank fixing bolt is torqued to 500 kg cm and does not come loose, but the crank develops the rotational movement because of the slop in the splines. I suppose loctite could be used on the splines but that would defeat the purpose of having a splined shaft and would require something more than the crank removal part to take it apart.


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## dominique (Aug 17, 2006)

*Is there anyone happy with that Crank?!*

Is there anyone happy with that crankset (k-force megaxo) ? Is it possible that the problem of the crank becoming loose was solved with the second (or third) generation ? I would like to know if among those who have problem with the crank there is someone who has a second generation ? There is a 5 or 6 digits code engraved on the back of the second generation crank. I just want to know if I should trust the guy at FSA who told me that the problem was solved on more recent models.
Many thanks.
d.


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## rcnute (Dec 21, 2004)

I've had two bikes with that crankset. Same problem. Very strange since the rest of FSA's stuff is pretty top-notch.


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## nenad (May 5, 2004)

dominique said:


> Is there anyone happy with that crankset (k-force megaxo) ? Is it possible that the problem of the crank becoming loose was solved with the second (or third) generation ? I would like to know if among those who have problem with the crank there is someone who has a second generation ? There is a 5 or 6 digits code engraved on the back of the second generation crank. I just want to know if I should trust the guy at FSA who told me that the problem was solved on more recent models.
> Many thanks.
> d.


I have SL-K and I've had no issues so far. Close to 1000 miles on them. I bought them in november last year.


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## VaughnA (Jun 3, 2003)

SLK with about 3000 miles so far. No problems. Never tightened since the initial installation.


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## jeff262 (Dec 19, 2005)

I have two of these cranks. The first one is about 2 years old with about 5k miles on it with no problems. The second is about 6 months old with about 2k miles on it with no problems.


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## dominique (Aug 17, 2006)

Sorry, I just realized that we were talking about the SLK crankset, and not about the K-Force Carbon Crankset w/MegaExo BB. Does the same problem happen with the k-force as well ? Is anyone would recommend the K-Force Carbon Crankset w/MegaExo BB for someone who looks for performance as well as durability ? Or should I simply try to find a 2005 Pro team Isssue, about which all seem very happy ?
Thank you.
d.


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## Insight Driver (Jan 27, 2006)

I have the FSA Gossamer crankset and have the same problem with the left crankarm coming loose. Apparently this is a problem for there are a lot of folks talking about it. I've been checking mine regularly. If I hear a creak from my bike when I am standing on the pedals and pushing hard I check the tightness. I will eventually change over to Shimano at some point when I am totally disgusted with the FSA design.


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## dominique (Aug 17, 2006)

Well, I guess I'll give up this idea to get one of those. I'll rather go with an old FSA Pro team issue, with which everone seems very pleased.
Thank you.
d.


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## gmcastil (Jan 8, 2006)

I spoke with the head of QC and FSA at length about the crankset issue that I've been hearing about time and again. Here's the thrust of the conversation:

- Splined interfaces cannot be machined perfectly. Moreover, if they could, it would be nearly impossible to separate them (eg, machinist blocks).

- Invariably, what ultimately happens, since there is some variance in the manufacturing process, is that a few of the splines and keys carry all the load, while a few of the others aren't touching. Eventually, through normal usage under these conditions, the crankarm tends to walk off the spindle.

- These types of joints are quite common in the automotive industry where they are exposed to much higher RPMs

- The correct approach that automotive engineers take to addressing this problem is, as many have said, to use Loctite 640 to fill the gaps between the splined interface and the crankarm.

- As most of us know, Loctite 640 is somewhat permanent, requiring heat to remove.

- According to the QC guy, FSA has been working with Loctite to come up with a similar flavor Loctite 641, that accomplishes the same task, but doesn't require heat to work with.

- Apparently, the designers weren't happy with this approach. They, like many, suppose Loctite to be an adhesive and a hack-job, rather than a sound design implementation. In order to prove the point, he intentionally machined a crankarm out of tolerances, installed it correctly with Loctite 641, and commuted 15 miles each way *without crankbolts*.

Needless to say, I was impressed that the guy on the other end of the phone actually knew what he was talking about. I came from a welding/machining background, so I typically know more about whats going on than these guys do. I'm pretty used to being snow-jobbed when I talk to manufacturers. Not so at all. I've seen a lot of these crankarms and haven't seen the problem a ton. He sent me a thing of Loctite 641 to use on a couple of these things and there has been mention that it'll be standard supply to shops and vendors which spec these cranks. All in all, I think that the final say on this has come down to what he said. The correct approach here is to apply Loctite and then torque the crankbolt correctly.


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## nenad (May 5, 2004)

*What about grease ?*



gmcastil said:


> I spoke with the head of QC and FSA at length about the crankset issue that I've been hearing about time and again. Here's the thrust of the conversation:
> 
> - Splined interfaces cannot be machined perfectly. Moreover, if they could, it would be nearly impossible to separate them (eg, machinist blocks).
> 
> - Invariably, what ultimately happens, since there is some variance in the manufacturing process, is that a few of the splines and keys carry all the load, while a few of the others aren't touching. Eventually, through normal usage under these conditions, the crankarm tends to walk off the spindle..


OK, this last paragraph is a very intersting point. I mentioned previously I had no issues with my cranks. However, right from the start I greased the threads and then tightened the screw quite hard. I've been riding my bike since January till now and not once have I had any issue with crank going loose. I am no expert, but perhaps all we need is a bit of grease ? Looking at the paragraph above, it makes sense that in my case it would be grease that would ensure proper fit of splines.


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## dominique (Aug 17, 2006)

So, does it mean that it is likely that the same problem will happen with the new Campy Ultra-torque 2007 ? As far as I understand, the Campy Ultra-torque crankset is quite similar to FSA megaexo... I am right ?


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## nenad (May 5, 2004)

dominique said:


> So, does it mean that it is likely that the same problem will happen with the new Campy Ultra-torque 2007 ? As far as I understand, the Campy Ultra-torque crankset is quite similar to FSA megaexo... I am right ?


You are wrong. The design is different in that the spindle is shared among two cranks (each crank has one half of the spindle attached to it and these two are then tightened by the screw in the middle of bottom bracket) as opposed to FSA which has the whole spindle attached to drive side crank and to which you attach the non-drive crank at the end. This non-drive side crank is what's problematic on FSA MegaExo cranksets.

I hope the explanation was clear enough.

Nenad


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## dominique (Aug 17, 2006)

nenad said:


> You are wrong. The design is different in that the spindle is shared among two cranks (each crank has one half of the spindle attached to it and these two are then tightened by the screw in the middle of bottom bracket) as opposed to FSA which has the whole spindle attached to drive side crank and to which you attach the non-drive crank at the end. This non-drive side crank is what's problematic on FSA MegaExo cranksets.
> 
> I hope the explanation was clear enough.
> 
> Nenad


Thanks Nenad.
That's good news. I am pleased to be wrong. 
d.


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## SDizzle (May 1, 2004)

Everything FSA is junk. ...I heard they're considering making a full gruppo for 2008?


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## gmcastil (Jan 8, 2006)

> OK, this last paragraph is a very intersting point. I mentioned previously I had no issues with my cranks. However, right from the start I greased the threads and then tightened the screw quite hard. I've been riding my bike since January till now and not once have I had any issue with crank going loose. I am no expert, but perhaps all we need is a bit of grease ? Looking at the paragraph above, it makes sense that in my case it would be grease that would ensure proper fit of splines.


I'd imagine that what is more likely is that your particular crank is closer to the ideal fit than others. You've likely overtightened the bolt, as well - not all that uncommon.


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## nenad (May 5, 2004)

gmcastil said:


> I'd imagine that what is more likely is that your particular crank is closer to the ideal fit than others. You've likely overtightened the bolt, as well - not all that uncommon.


Well, not any harder than I tighten bolts on my Campy Record cranks, and I've had those for 3 years...You got me worried....I just tried untightening to bolt on the FSA, no problems...


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