Chamberlain 248735 3/4 HP - Manual (Page 9)

9
To avoid SERIOUS damage to garage door opener, use ONLY
those bolts/fasteners mounted in the top of the opener.
ASSEMBLY STEP 2
Fasten the Rail to the Motor Unit
• Insert a 1/4"-20x2-1/2 bolt, washer and spacer into the
cover protection bolt hole on the back end of the rail as
shown. Install lower spacer and washer then tighten
securely with a 1/4"-20 lock nut. Do NOT overtighten.
• Remove the bolt and lock nut from the top of the motor
unit.
• Attach spreader to the motor unit with two screws.
• Place the “U” bracket, flat side down onto the bolt
mounted on the motor unit and align the bracket hole
with the bolt holes. Fasten with the previously removed
bolt and lock nut.
• Align the rail assembly with the top of the motor unit.
Slide the rail end onto the “U” bracket, all the way to the
stops that protrude on the top and sides of the bracket.
ASSEMBLY STEP 3
Install the Idler Pulley
• Lay the chain/cable beside the rail, as shown. Grasp the
end with the cable loop and pass approximately 12"
(30 cm) of cable through the window. Allow it to hang
until Assembly Step 5.
• Remove the tape from the idler pulley. The inside center
should be pre-greased. If dry, regrease to ensure proper
operation.
• Place the idler pulley into the window as shown.
• Insert the idler bolt from the top through the rail and
pulley. Tighten with a 3/8" lock washer and nut
underneath the rail until the lock washer is compressed.
• Rotate the pulley to be sure it spins freely.
• Insert a 1/4"-20x1-3/4 bolt into the trolley stop hole in
the front of the rail as shown. Tighten securely with a
1/4"-20 lock nut.
Bolt
Hex Screws
8-32x7/16
Chain
Spreader
Motor Unit
Sprocket
"U" Bracket
Lock Nut
Lock Nut
SLIDE RAIL TO STOPS
ON TOP AND SIDES
OF BRACKET
Cover
Protection
Bolt Hole
Bolt
Spacer
Spacer
Washer
Washer
Lock
Washer
3/8"
Nut 3/8"
Cable Link
Idler
Bolt
Chain and
Cable
Pulley Rail
Bolt
Nut
Washer
Trolley
Idler
Pulley
Idler
Pulley
Grease
Inside Pulley
Screwdriver
Trolley
Stop Hole
Bolt
Lock
Nut
Bolt 1/4"-20x2-1/2
Spacer Washer 5/8" Lock Nut 1/4"-20
HARDWARE SHOWN ACTUAL SIZE
Nut 3/8" Lock Washer 3/8" Idler Bolt Lock Nut 1/4"-20 Bolt 1/4"-20x1-3/4"
HARDWARE SHOWN ACTUAL SIZE