Eccentric / Timing Chain Adjustment
Loosen the set screws under the bottom bracket shell. There are two of them, and 1 full turn should be plenty. If you are already confused, this would be a good time to visit your bike shop and watch them do it.
The eccentric should be rotated so the spindle is above the bottom bracket shell centerline (see drawing below).
You can use either a pin spanner wrench or a 36mm headset wrench to rotate the eccentric.
Rotate the eccentric according to the drawing to tighten or loosen the timing chain. The timing chain should be loose enough to prevent binding and tight enough to keep from falling off.
The chain should move about 1/2" for the front and 1/4" for the rear without using force.
When you think the eccentric is adjusted, snug up the set screws (do not tighten yet) and rotate the cranks to see if there is a tight spot.
CAUTION: Take care to not catch your fingers between the chain and chainring. IT CAN CUT YOUR FINGER OFF.
If the chain is tight in one spot, readjust the eccentric and check again. Once it is adjusted, tighten the set screws and check one more time. Adjust again if necessary.