Chamberlain B1381C Owner's Manual page 9

Assembly
STEP 5 Tighten the Belt
1. By hand, thread the spring trolley nut on the threaded shaft until it is finger tight against the trolley. Do not
use any tools. Remove the screwdriver.
2. Insert a flathead screwdriver tip into one of the nut ring slots and brace it firmly against the trolley.
3. Tighten the spring trolley nut with an adjustable wrench or a 7/16" open end wrench about a quarter turn
until the spring releases and snaps the nut ring against the trolley. This sets the spring to optimum belt
tension.
Nut Ring
BEFORE
1" (2.5 cm)
Nut Ring Slot
Spring
Trolley Nut
Nut Ring
AFTER
1-1/4" (3.18 cm)
STEP 6 Install the Sprocket Cover
To avoid possible SERIOUS INJURY to finger from moving garage door opener:
ALWAYS keep hand clear of sprocket while operating opener.
l
Securely attach sprocket cover BEFORE operating.
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1. Position the sprocket cover over the sprocket as shown and fasten to the mounting plate with #8x3/8" hex
screws provided.
You have now finished assembling your garage door opener. Please read the following warnings before
proceeding to the installation section.
9
HARDWARE
Hex Screw #8x3/8"
(Packed with the sprocket cover)
Hex Screw
Sprocket Cover