Chamberlain 3850 Garage Door Opener User Manual


 
6
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 on top of
motor unit.
Align rail and styrofoam over belt pulley. Cut tape from
rail, chain 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 belt pulley.
To avoid SERIOUS damage to opener, ONLY use bolts
mounted in top of motor unit.
WARNING
CAUTION
WARNING
WARNING
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.
Washered Bolt
5/16"-18x1/2"
Rail Hole
Motor U
nit
Belt Pulley
Rail Hole
USE ONLY THIS
TYPE AND SIZE
BOLT
Trolley
Threaded
Shaft
Spring/Trolley Nut
The Chamberlain Group, Inc.
Liftmaster Synchro Drive
Spring Trolley Nut Assembly
3/5/92 - 5/16 /92 - 5/21/92 - 6/2/92
6/11/92
Nut
Ring
Trolley
Threaded
Shaft
Nut Ring
Slots
Square
End
Nut Ring Trolley
Nut Ring
Trolley
1" (2.5 cm) 1-1/4" (3.18 cm)
BEFORE AFTER RELEASE
Figure 1
Figure 2
Figure 3