[DelawareDager]

I'm a newb :aureola: so be easy and don't rip me a new one if the solution is something simple. Got my 1st road bike (K2 mod 6.0) the crankset is a FSA S-LK. So i bring it home from the LBS and within a few days of riding, nothing serious, just the left side crank arm is noticeably loose :mad2: . So i tighten it, not too tight as I don't have a torque wrench yet and don't want to mess anything up but I'm sure it was tight enough and I got out for a few miles and its loose again. Any pointers at all as to what i should do?

 

[Dr_John]

This unfortunately is a common occurrence with FSA MegaExo-based cranks. Do a search and you'll find plenty of threads on the topic:

http://forums.roadbikereview.com/showthread.php?t=135068&highlight=FSA+crank+arm+loosening

http://forums.roadbikereview.com/showthread.php?t=137571&highlight=FSA+crank+arm+loosening

http://forums.roadbikereview.com/showthread.php?t=127002&highlight=FSA+crank+arm+loosening

http://forums.roadbikereview.com/showthread.php?t=91806&highlight=FSA+crank+arm+loosening

 

[JimP]

I sounds like the splines on the shaft and crankarm do not fit closely enough. If this is the case, you will never be able to keep the crankarm from loosening. FSA may say to use blue loctite on the splines but the real issue is poor machining and poor quality control. You may have to send the crankset back to FSA for replacemnent.

 

[ericm979]

The crank is probably toast- once loose the splines will wear quickly. But you can try- follow FSA's assembly instructions which include both low-strength loc-tite on the splines and torquing to a specific value (either 32 or 36 ft-lbs, I forget). You can find the instructions on FSA's web site.

But since it's a new bike I'd just take it to the shop you bought it from and have them deal with it.

 

[ms6073]

The crank is probably toast- once loose the splines will wear quickly.

Going to respectfully disagree. Not going to defend the design as obviously with so many posts about loose crankarms, FSA missed the mark but I will say that those with SLK light and K-Force light that includes a redesigned BB-8200 bottom bracket are not reporting this issue. As for following FSA's assembly instructions - that is probably what got the orginal poster to this point in the first place and it seems obvious that it is time to think outside the box in order to get the cranks properly installed. To that end I will offer the same advice I gave to another forum member from this thread - https://forums.roadbikereview.com/showthread.php?t=135068&highlight=FSA+crank+arm+loosening - linked above.

Based on my experience with my FSA SRM Pro, K-Force, SLK and K-Force Light - all orginally with BB-8000 bottom brackets except for the K-Force Light crankset which comes with the new BB-8200 - reference the diagram below in which the splines on the spindle are circuled for emphasis:

Regardless of which bottom bracket is being used - original BB-8000 or BB-8200 - when the spindle is inserted into the bearing cups of the bottom bracket, look at the splines as they protrude from the non-drive side bearing cover. If you cannot see the splines as well as 3-5mm of smooth/non-splined spindle protruding from the plastic bearing shield, then proper torque of the non-drive side crankarm will not be possible as the crankarm will start binding against the face of the bearings long before the crankarm is able to fully seat on the splined end of the spindle!

In my experience, when I tighten the crank bolt, the crankarm seats completely afterwhich the crankarm bolt bottoms at which point any additional torque will do nothing but fatigue the bolt and most likely result in a cracked crankarm bolt (yes I have done this)! For the orginal poster, read the linked thread and the OP does not feel comfortable removing the crankarm to inspect the splines, take the bike back to the LBS and ask to look over the techs shoulder when the crankarm is removed because inadequate spindle clearance on the non-drive side will prevent proper installation. finally, FSA has a 2-year warranty on these cranks and while they prefer dealing with bike shops, there is no reason that a consumer cannot call to get a warranty issue resolved.

 

[danl1]

In my opinion, it's also necessary to place the blame on the SL-K design rather than Mega-Exo. Gossamer cranksets, for example, use Mega-Exo and a Shimano-like pinch-bolt design on the left crank that doesn't have this problem.

A lot of folks (shop rats and consumers alike) are afraid or don't have the proper tools to drive the crank into the driveside bearing, and instead try to use the torque of the screw to bring things together. IMO, that's the cause of a lot of the trouble this design sees. Gotta admit it's daunting to take a mallet to a carbon spider, but getting it seated properly is important.

 

[DelawareDager]

Thanks for all the replies, I talked via email to person at FSA and she told me "It sounds like it may not have been installed using the most updated (fall 2006) installation instructions or installed properly. The best thing would be for the shop to give the FSA tech department a ring and those folks can walk the mechanic through the installation and checking of the crank to make sure it is not damaged from being ridden loose.

So I think thats what I will most likely do, as I'm not that knowledgable when it comes to the inner workings of cranks.

 

[ms6073]

Thanks for all the replies, I talked via email to person at FSA and she told me "It sounds like it may not have been installed using the most updated (fall 2006) installation instructions or installed properly.

Well thats certainly an interesting take on the situation considering the latest revision for the Carbon MegaExo crank installation file is dated February 2007 (you can download the latest installation giude here http://road.fullspeedahead.com/downloadfly.aspx?download=downloads/Install_MegaExoCarbon.pdf). More importantly, as already stated following the FSA intructions verbatim will simply verify the current problem as most likely your bottom bracket shell is narrower than what FSA expects. The solution will probably require that you either (A) have the mechanic inspect the insertion of the spindle to assure proper spindle insertion (splines +3-5mm smooth spindle surface) which in my experience requires omitting the inner (and pssibly outter alloy sleeves) or (B) take the advice of others and switch to another manufacturers crankset!

Gotta admit it's daunting to take a mallet to a carbon spider, but getting it seated properly is important.

Um - what? Maybe I misundertand but it seems to me that applying blunt force to the face of the crankarm in an attempt to completely 'seat' the bearing in the bearing cup will only result in damaged bearings! Furthermore, having used a bearing press designed specifically for an external bearing bottom bracket to check that the bearing is properly seated, I have not found this to be the probelm.

 

[function]

In my opinion, it's also necessary to place the blame on the SL-K design rather than Mega-Exo. Gossamer cranksets, for example, use Mega-Exo and a Shimano-like pinch-bolt design on the left crank that doesn't have this problem.

The Gossamer have the same issues (i have one).

 

[DelawareDager]

I've recently took my bike to the LBS to talk about the crank and everything I've learned from you guys and he had the idea to add a spacer and he said just see how it goes and if not we'll try the other options and so far so good, its been working fine. Ridden about 100+ miles and no problem.