Chamberlain B1381C Owner's Manual page 7

Assembly
STEP 2 Fasten the Rail to the Motor Unit
To avoid SERIOUS damage to garage door opener, use ONLY those bolts/fasteners mounted in the top of the
opener.
1. Insert a 1/4"-20 x 1-3/4" bolt into the cover protection bolt hole on the back end of the rail as shown. Tighten
securely with a 1/4"-20 lock nut. DO NOT overtighten.
2. Remove the bolts from the top of the motor unit.
3. Use the carton to support the front end of the rail.
4. Place the "U" bracket, flat side down onto the motor unit and align the bracket holes with the bolt holes.
5. Fasten the "U" bracket with the previously removed bolts; DO NOT use any power tools. The use of power
tools may permanently damage the garage door opener.
Bolt
"U" Bracket
Cover
Protection
Bolt Hole
Lock Nut
HARDWARE
Bolt
1/4"-20x1-3/4"
Bolts (Mounted in the garage door opener)
STEP 3 Install the Idler Pulley
1. Lay the belt beside the rail, as shown. Grasp the end with the hooked trolley connector and pass
approximately 12" (30 cm) of belt through the window. Keep the ribbed side toward the rail, and allow it to
hang until Assembly Step 4.
2. Remove the tape from the idler pulley. The inside center should be pre-greased. If dry, regrease to ensure
proper operation.
3. Place the idler pulley into the window as shown.
4. 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.
5. Rotate the pulley to be sure it spins freely.
6. Locate the rail tab. The rail tab is between the idler bolt and the trolley in the front rail section. Use a
flathead screwdriver and lift the rail tab until the tab is vertical (90º).
Lock Nut
1/4"-20
Lock Washer
7
HARDWARE
Nut 3/8"
Bolt
Rail Tab
Belt
Bolt
Nut Trolley Connector
Lock Washer 3/8"
Rail
Grease Inside Pulley
Idler Pulley