Safety: Disconnect power before adjusting chain or belt tension.

Locate tensioner: Find the adjustment bolt or nut at the end of the BFT rail (near the door or operator head).
Adjust tension: Tighten the tensioner gradually until the chain/belt has about 6–12 mm of deflection at the midpoint when pressed lightly.
Do not overtighten: Excessive tension can damage the motor and rail. Follow BFT's specified tension values.
Test run: Reconnect power and run the door through a full cycle, listening for smooth operation.

Garage door opener chain or belt is sagging and slaps against the rail during operation.

Possible Causes