Chamberlain HD420EVP Owner's Manual page 10

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.
You have now finished assembling your garage door opener. Please read the following warnings
before proceeding to the installation section.
To Tighten Outer Nut
Chain
Base of Rail
9
Trolley
Outer Lock
Threaded
Nut Washer
Shaft
Inner Nut
To Tighten
Inner Nut
1/4" (6 mm)
Mid length of Rail