Craftsman 1/2 HP GARAGE DOOR OPENER 139.53978SRT - Manual (Page 9)

Assembly Step 2
Fasten the Rail to the Opener
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.
Remove the two screws from the top of the
opener.
Place the U bracket, fiat side down, on the opener
and align the bracket holes with the screw holes.
Fasten with the previously removed screws.
Attach spreaders to the U bracket by snapping
them into piace.
Aiign the rail assembly with the top of the opener.
Slide the rail end onto the U-bracket, all the way
to the stops that protrude on the top and sides of
the bracket
Hardware Shown Actual Size
mm
BaltlM’-20x1-3M
Lock Nut
1/4‘-Z0
To fasten rail, use only those screws mounted
in the top of the opener. Any other screws will
cause serious damage to the opener.
Screws Opener
Sprocket
Hook Spreader
into Back Slots,
then Snap Tab
Into Front Slot
Lock Nut
Assembly Step 3
install the Idler Pulley
Lay the chain/cable beside the raii, as shown.
Grasp the end with the cable loop and pass
approximately 12" 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.
Piace 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.
Chain and
Cabte
3/8" Lock
Washer
Hardware Shown Actual Size
V7 Idler Bolt
Bolt l/4"-20x 1-3/4 Lock Nut l/4"-20 Nut 3/8' Lock W asher 3/8"