Assembly; Attach The Rail To The Motor Unit; Set The Belt Tension - Chamberlain 3280CM 1/2 HP Owner's Manual

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.
• 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 fi nger 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 fi rmly 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.
Nut Ring
Trolley
BEFORE
1" (2.5 cm)
Figure 3
Nut Ring
Trolley
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
Washered Bolt
5/16"-18x12"
Sprocket
Rail
Hole
Rail Hole
Trolley Threaded Shaft
Spring/Trolley Nut
Nut
Ring
Square End
Trolley
Threaded
Shaft
Nut Ring Slots