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Fasten the rail to the motor unit, Install the idler pulley, Assembly step 2 – Chamberlain WHISPER DRIVE 248754 User Manual

Page 9: Assembly step 3

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9

ASSEMBLY STEP 2

Fasten the Rail to the Motor Unit

• Insert a 1/4"-20x1-3/4" 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.

• Remove the two bolts from the top of the motor unit.

• Place the “U” bracket, fl at side down, on the motor unit

and align the bracket holes with the bolt holes. Fasten
with the previously removed bolts.

• 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 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 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.

To avoid SERIOUS damage to garage door opener,
use ONLY those bolts/fasteners mounted in the top of
the opener.

Bolt 1/4"-20x1-3/4"

Lock Nut
1/4"-20

“U” Bracket

SLIDE RAIL TO
STOPS ON TOP
AND SIDES
OF BRACKET

Cover
Protection
Bolt Hole

Lock Nut

Motor Unit
Belt Pulley

Bolt

Bolts

Lock
Nut

Screwdriver

Bolt

Bolt

Idler
Bolt

Idler
Pulley

Idler
Pulley

Pulley

Lock
Washer
3/8"

Washer

Grease
Inside
Pulley

Nut
3/8"

Nut

Trolley
Stop
Hole

Trolley
Connector

Rail

HARDWARE SHOWN ACTUAL SIZE

HARDWARE SHOWN ACTUAL SIZE

Bolt 1/4"-20x1-3/4"

Lock Nut 1/4"-20

Lock Washer 3/8"

Nut 3/8"

Idler Bolt