Chamberlain 87504-267 Manual page 13

Assembly
3 Tighten the Chain
1. Loosen the inner nut and lock washer on the trolley threaded shaft.
2. Tighten the outer nut until the chain is a 1/2" above the base of the rail at the midpoint of the rail.
3. Re-tighten the inner nut.
Slack in the chain is normal when the door is closed. No readjustment is necessary.
1/2" (13 mm)
13