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Discussion Starter · #1 ·
I have a new bike with FSA Mega Exo crank set. I noticed that the crank is slightly loose. If I keep the pedal arms horizontal, and push/pull away from the frame, the pedal arm moves a bit. Not much, less than one millimeter. But it's still enough for me to notice when cycling.

Is it harmful to use the bike in this condition? Should I let it stay put until I get it back to the store? Or will a couple of days of use be ok?

What is likely to be the problem with the crankset?

Thanks!
 

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DO not ride it like that. The splines will wear out. Try torquing the bolt down to the value printed on the bolt. (it translates to 35 ft-lbs.). That's what FSA told me when I emailed them about my FSA mega-exo crank.

Mine kept coming loose. Check yours once a week. If it comes loose and you ride on it you'll ruin the splines. Mine is off to FSA for warranty. When I get the replacement back I'm going to sell it. It's a nice stiff crank but the older FSA carbon pro I put on to replace the SLK is lighter and is going to stay on.

There are two problems with this crank-- the left bolt comes loose, and some of the axles have been manufacturered with splines that were too small (according to my LBS).
 

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Discussion Starter · #4 ·
Thanks for your comments.

BTW, just to be sure that I explain the situation well enough. I think that I was not precise enough in the first post.

The bottom brackets are not loose. And both pedal arms are well connected to each other. If I push/pull one pedal arm, the other will also move, as will the chain rings.

Sorry I was not precise enough in the beginning.
 

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fredriglo said:
Thanks for your comments.

BTW, just to be sure that I explain the situation well enough. I think that I was not precise enough in the first post.

The bottom brackets are not loose. And both pedal arms are well connected to each other. If I push/pull one pedal arm, the other will also move, as will the chain rings.

Sorry I was not precise enough in the beginning.
Sorry to be harsh, but if you can't diagnose the problem, you should take it into a shop and have it looked at. My suspicion is that the non-drive side crankarm bolt is loose. FSA is notorious for this, but to their credit their customer service will send you a replacement one, made in steel, for free.

The Carbon Compact Pro models have this issue, although the mechanism is a little different. But the other posters are correct that it will eventually wear out the splines, which is bad news.
 

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fredriglo said:
The bottom brackets are not loose. And both pedal arms are well connected to each other. If I push/pull one pedal arm, the other will also move, as will the chain rings.
That's exactly the symptom I had the first couple times my left crank arm came loose. Check the bolt. The tightness of the bolt (or rather of the left crank arm) determines the free play of the axle through the bearings.
 

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I have the same issue. The left crank is bolted on and there are two screws that clamp the arm to the splines. I had my crank arm bolt actually come off on me while riding. I had tightened a couple of weeks earlier. My bike shop said there have been multiple reports of the left crank arm coming loose. I'm checking my new one over other ride or so now. It seems to be a good design but I wonder if the torque specs or the order of tightening have to be clarified by the manufacturer. At any rate if my arm tends to keep coming loose I'm going to get the crankset replaced by a Shimano Ultegra one that doesn't have any issue with loosening up as the FSA MegaExo design seems to do.
 

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Discussion Starter · #9 ·
ericm979 said:
The tightness of the bolt (or rather of the left crank arm) determines the free play of the axle through the bearings.
Thanks for your comment. I did take it back, and they did fix the problem. Too bad it's a "super market" kind of shop, so I couldn't talk to the mechanic who actually did the work.

Does the tightness of the left arm also determine the tightness of the bearings? A bit like how the Aheadset bearings work? If so, it seems that I could have fixed the problem by adjusting the tightness of the left pedal arm.
 

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fredriglo said:
Does the tightness of the left arm also determine the tightness of the bearings? A bit like how the Aheadset bearings work? If so, it seems that I could have fixed the problem by adjusting the tightness of the left pedal arm.
Yes. My post must not have been clear, since that's exactly what I was trying to tell you.

Check it frequently, and use a torque wrench on it.
 

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Discussion Starter · #11 ·
Your post was useful. I just wanted to be 100% sure that I had understood correctly.

There's and endcap on the left pedal arm as well, which should help keep the arm tight, I suppose.

Seems like I need a torque wrench, if this problem continues. Let's hope it's a one-off issue, though.
 
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