Take the plastic housing and firmly press in the 3/8" bearing. If needed, press in with a hammer and block of wood.
Slide the end of the output shaft into the 3/8" bearing.
Slide on the 56 tooth gear, aligning the hex of the gear and the shaft.
Generously grease the gear, fully surrounding it with lubricant.
(Note: the gearboxes come with a small packet of grease, but it is a worthwhile investment to get more.)
Press the 1/2" bearing into the aluminum plate, making sure the bearing's flange is on the same side as the aluminum plate's flange.
Slide the aluminum plate and 1/2" bearing onto the output shaft, with the flange towards the plastic housing.
Align the plastic housing's 4 nubs with the 4 holes on aluminum plate.
Install 10-32 nylock nuts with the nut holes in the back of the plastic housing, and screw in 5/8" 10-32 socket head screws.
To apply the 12 tooth pinion gear to the CIM motors shaft, insert the 2mm machine key into the CIM motor keyway. Then slide the pinion over top, and then press on the 8mm retaining ring to hold the pinion in place. A 3/8" nut driver can be used to push the ring into place.
Insert the CIM motors into the back of the plastic housing and fasten them in place using 5/8" 10-32 socket head screws with nylon patches (two per motor).
Place a .595" spacer on the gearbox output shaft, then inserting a 1/8" machine key into the output shafts keyway. Slide a #35 12 tooth double sprocket of the key, and then place a 3/16" spacer on the shaft.
Place a 1/4" washer on a 1/4-20 button head screw and apply a small amount of thread locking fluid to the screw. Fasten the screw in the end of the output shaft to secure the sprocket and spacers on the shaft.