Chamberlain LiftMaster Professional Security+ 2580C 1/2 HP Manuel D'instructions page 6

ASSEMBLY STEP 1
Attach the T-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 T-rail and styrofoam over sprocket. Cut tape
from T-rail, chain and styrofoam.
• REMOVE STYROFOAM.
• Insert both washered bolt through the T-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"
Figure 3
Trolley
Nut Ring
AFTER RELEASE
1-1/4"
WARNING
CAUTION
To avoid SERIOUS damage to opener, ONLY use bolts
mounted in top of motor unit.
USE ONLY THIS
TYPE AND SIZE
BOLT
Spring/Trolley Nut
Figure 1
Figure 2
6
Trolley
Threaded
Shaft
Trolley
Threaded
Shaft
Nut
Ring
Square
End
Nut Ring
Slots