Chamberlain C870 Owner's Manual page 9

Assembly
STEP 5 Tighten the chain
1. Spin the inner nut and lock washer down the trolley threaded shaft, away from the trolley.
2. To tighten the chain, turn the outer nut in the direction shown.
3. When the chain is approximately 1/4" (6 mm) above the base of the rail at it's midpoint,
retighten the inner nut to secure the adjustment.
Sprocket noise can result if the chain is too loose. When installation is complete, you may notice some
chain droop with the door closed. This is normal. If the chain returns to the position shown when the
door is open, do not re-adjust the chain.
NOTE: During future maintenance, ALWAYS pull the emergency release handle to disconnect the
trolley before adjusting the chain.
To Tighten Outer Nut
Chain
Base of Rail
Trolley
Lock
Outer
Threaded
Washer
Nut
Shaft
Inner Nut
To Tighten
Inner Nut
1/4" (6 mm)
Mid length of Rail
STEP 6 Install the sprocket cover
To avoid possible SERIOUS INJURY to finger from moving garage door opener:
ALWAYS keep hand clear of sprocket while operating opener.
l
Securely attach sprocket cover BEFORE operating.
l
1. Position the sprocket cover over the sprocket as shown and fasten to the mounting plate with
8x3/8" hex screws provided.
You have now finished assembling your garage door opener. Please read the following warnings
before proceeding to the installation section.
9
HARDWARE
Hex Screw #8x3/8"
(Packed with the sprocket cover)
Hex Screw
Sprocket Cover