Chamberlain LiftMaster Security + 3270 1/2 HP Manuel D'instructions page 6

ASSEMBLY STEP 1
Attach the Rail to the Motor Unit
To avoid installation diffi culties, do not run the garage
door opener until instructed to do so.
1. Remove the two washered bolts mounted in top of
motor unit.
2. Align rail and styrofoam over sprocket. Cut tape from
rail, belt and styrofoam. REMOVE STYROFOAM.
3. Insert washered bolts through the rail into the motor
unit. Tighten bolts securely.
Use only these bolts! Use of any other bolts will cause
serious damage to door opener.
4. Position belt over the motor unit sprocket.
ASSEMBLY STEP 2
Set the Belt Tension
1. By hand, thread the spring trolley nut on the threaded
shaft until it is fi nger tight against the trolley (Figure 1).
Do not use any tools.
2. Insert a screwdriver tip into one of the nut ring slots
and brace it fi rmly against the trolley (Figure 2).
3. Place a 7/16" open end wrench on the square
end. Rotate about 1/4 turn until the spring releases and
snaps the nut ring against the trolley (Figure 3).
This extends the spring for optimum belt tension.
Trolley
Nut Ring
BEFORE 1"
(2.5 cm)
Figure 3
Trolley
Nut Ring
AFTER RELEASE
1-1/4" (3.18 cm)
To avoid SERIOUS damage to opener, ONLY use
bolts/fasteners mounted in top of motor unit.
USE ONLY THIS
TYPE AND SIZE
BOLT
Figure 1
Figure 2
6
Trolley
Threaded
Shaft
Spring/Trolley Nut
Trolley
Threaded
Shaft
Nut
Ring
Square
End
Nut Ring
Slots