Assembly; Set The Belt Tension - Chamberlain LiftMaster Security+ 2500DC Owner's 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 both 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).
Figure 1
Spring/Trolley Nut
• 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
Threaded
Shaft
WARNING
CAUTION
To avoid SERIOUS damage to garage door opener,
use ONLY those bolts/fasteners mounted in the top of
the opener.
Washered Bolts
5/16"-18x1/2"
Figure 2
Figure 3
Trolley Nut Ring
BEFORE
1" (2.5 cm)
6
Motor Unit
Sprocket
Foam Packaging
Trolley
Threaded
Shaft
Nut
Ring
Square
End
Nut Ring
Slots
Trolley
Nut Ring
AFTER RELEASE
1-1/4" (3.18 cm)