A couple of weeks ago I started noticing a hitch in the pedals when I stopped pedalling. I could pedal forward or backward and feel what I can only describe as a bump in the drivetrain. Thought maybe the chain was off, but no. Didn't feel anything when I was pedalling normally, only when I slowed my pedalstroke and let my left foot rest at bottom dead center. When I backpedal and then pedal, it's much more apparent. I thought I'd pull the crank yesterday to check it out and see what's up. I put a hand on each pedal to see if I could feel it that way and it feels as if the splines are worn and the crankarm is rotating back and forth a bit on the spindle. This explains why it's noticeable when I backpedal and pedal forward again slowly.
CN: put hands one either pedal and the left crankarm shifts a bit. Rotate cranks 180 degrees and repeat to get same effect. What the heck?
Yeah, the shell was faced. LBS called FSA and they think that it could be the aluminum spline in the left crankarm working its way loose, not anything with the splines or the bearings. It's not the easiest thing to try to explain, but FSA initial idea makes more sense than wearing splines. The crankarm hasn't ever worked its way loose or anything.