I have a bike here fitted by OEM with:
- FSA Omega Adventure MegaExo crank
- FSA BB-4000
No maintenance or mods done around BB area on this bike. If you are curious it is Pinnacle Neon 5 2019-version. Only around 5000 km on it from new.
The crank never really spinned well from the start on that bike. Without the chain in place it does at most 1/4 of a turn before coming to a stop. I have been asked to look into it recently. I initially thought to write it off as FSA lower-end cranks being garbage in general... But eventually took it apart to take a look. The findings are interesting...
The NDS crank arm has a self extracting mechanism (like most FSA Crank arms do) and against the expectations it worked pretty well. I was able to pull of the NDS crank arm and then take the DS arm out with the axle (no mallet needed). I checked the BB in the shell without axle and it appears to be silky smooth. I did the usual TLC on the BB and crankset:
- Removed BB from the shell
- Cleaned the threads on BB, shell, self extractor nut, spindle and retaining bolt.
- Greased the threads
- Greazed the axle
- Put everything back together
The crank spins silky smooth until the point when I tighten the NDS crank arm retaining bolt. FSA spec says 40-50 Nm. The crank stops spinning properly around 10Nm which is way too low to be secure in my view.
There is a wave washer between NDS crank arm and the BB face which is supposed to preload the bearings. This wave washer is fully compressed and looks flat at 10Nm. Anything above that and I am compressing the bearings. By the time I reach ~40Nm the cranks is back to the same state as pre-maintenance - it does about 1/4 turn without chain in place.
From the situation described above I am very confiden that the issue is simply with the NDS crank arm sitting too close to to the axle centre when tightened to correct torque setting. Bearings are overloaded and cannot spin free. Could be a manufacturing tolerance issue. There is definitely no alignment problem as the crank arms spin well when the retaining bolt is at 10Nm...
I am really surprised as to how bearings did not get damaged after riding ~5000km in this state but this is off topic.
Any ideas on how to cure this problem? Anyone has experience with FSA cranks?
If there were any spacers, I would start by removing them to allow more room for that crank arm and wave washer, but there are none... Either none came with the crank, or not fitted by whoever was assembling it. And rightly so - spacers would have made it tighter.
Measured the frame with vernier caliper. It's 67.93mm so pretty close to expected 68 (allowing for the tool and measurement accuracy).