Chamberlain 3850 - Manual (Page 6)

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.
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 Unit
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
WARNING
CAUTION WARNING
WARNING