Assembly; Attach The Rail To The Motor Unit; Set The Belt Tension - Chamberlain 3280-390 1/2 HP User Manual

ASSEMBLY STEP 1

Attach the Rail to the Motor Unit

To avoid installation difficulties, do not run the garage
door opener until instructed to do so.
• Remove the two washered bolts mounted in top of
motor unit.
• Align rail and styrofoam over sprocket. Cut tape from
rail, belt and styrofoam.
• REMOVE STYROFOAM.
• 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.
• Position belt over the motor unit sprocket.
ASSEMBLY STEP 2

Set the Belt Tension

• By hand, thread the spring trolley nut on the threaded
shaft until it is finger tight against the trolley (Figure 1).
Do not use any tools.
• Insert a screwdriver tip into one of the nut ring slots and
brace it firmly against the trolley (Figure 2).
• 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