Problems with gears after re-attaching front chainring
I had the same issue (taking cranks off, pulling / cleaning bottom bracket, replacing it only to find that the front derailleur didn't match up no matter how much I adjusted it in and out) - it turns out that the cranks weren't tightened fully, allowing / causing the chain ring to stick out slightly farther than tolerances allowed for. The solution was to crank it down using a torque wrench - find the torque specification for the crank bolts (mine was 40 ft/lbs amazingly) and crank them down. You'll be surprised at how much difference this can make.