Mountain Biking - FSA mego exo BB
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05-14-09, 04:01 PM
I just installed this BB on my single speed MTB. The cranks turn ok I guess, but they don't exactly spin great. I feel like if the chain is not on I should be able to just give it a nudge and get them spinning, and that's just not happening. I'm wondering if I screwed something up of if FSA bearings are just crap.
^^ You just cinched things down too tight. It's not the bearings' fault: ball bearings can only take so much side-load pressure.
The bearing pressure on an FSA Mega-EXO is similar to how pressure is applied in tightening a headset. The BB spindle stays with the drive-side crank arm and is passed through the bearing, as you did. NOW, when you put the non-drive-side crank arm on, you leave the pinch-bolts loose and tighten the cap (much like a headset top cap) to take up the side-play slack, then tighten the pinch bolts.
That was where you errored: ONLY snug the cap enough to eliminate the side-play. If you tighten the cap enough to where the BB does not spin freely, back the cap bolt off some until it does. Once you're sure you have the right balance of free-spinning and no side-play (runout), then tighten the pinch bolts on the crank. As an added measure, take another snug on the cap bolt afterward just to ensure it won't back out (it can't change anything once the pinch bolts are tight).
05-14-09, 04:21 PM
Thanks, I'm going to loosen them up some. I think I pushed the opposite crank arm in and tightened the pinch bolts first. Everything has been really easy except for the BB.
For your further edification (and in case you didn't get the instructions with your BB/crankset), here is the PDF of the installation instructions:
Top of page 3, steps 10/11 & 11.
05-14-09, 05:08 PM
Alright, I've loosened the cranks up and there is a little improvement. I'm still not pleased with the smoothness though. There is still a decent amount of resistance with no chain installed. It feels nothing like the super smooth FSA headset I installed.
^^ I'm presuming this is a brand new set, correct? Do you have the o-rings on each end of the spindle behind the crank arm (unless yours did not come with them)?
The only other thing I can imagine (provided you've backed off the pressure enough) is the inherent drag from the plastic dust caps. That is a strange FSA design that, although I like most of their stuff, I just cannot get on board with. The dust cap has a sleeve that actually goes inside the inner bearing race with the spindle - - the spindle is 19mm OD and the inner bearing race is 20mm ID, so there is actually 1mm of plastic taking up the 'slop' between the spindle OD and the bearing ID. This means that the whole dust cap disc spins around on the face of the outer BB cup. That's just plain screwy . . . it causes extra drag and premature dust cap wear from it constantly grinding against the BB cup.
I am rebuilding a Mega-EXO right now to eliminate that stupid interface. A good bearing doesn't need the dust cap anyway and I'm not going to pay upwards of $20 with shipping for two pieces of plastic that are destined to eventually self-destruct. Trouble is, I'm going to have to fabricate a 19/20 shim because none that thin-walled exist :notamused:
05-14-09, 06:16 PM
I was wondering what was up with the dust cap. Although I didn't realize it wrapped all the way around the bearing. Anyway, I took it apart again and put it back together. It is spinning well now, not amazing but hey its a pretty cheap BB. Let me know how you improve on the dust cap design. Thanks for the help.
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