First remove the chain from the opener, but put make a mark somehow on
the chain to put it back on the sprocket in the same place. Remove the
fork piece that holds the small limit gear at the bottom of the shaft &
remove the limit gear. Remove the three screws that holds the shaft
plate to the top of the motor head. Pull the whole shaft assembly out
thru the top. Put the shaft onto some blocks of wood & drive out the
roll pin in the bottom of the worn out gear. Change the gear &
re-assemble in the opposite order. You may have to make small
adjustments to the limits to get the door to open or close fully.

Doordoc
www.DoorsAndOpeners.com