Garage door opener chain slaps the rail loudly during starting and stopping.

Safety first: Disconnect power before adjusting chain tension. Do not overtighten the chain; it can damage the opener.

Steps to adjust chain slack:

• 1. Locate tensioner: On Stanley chain-drive models, find the adjustment nut on the trolley or at the end of the rail.
• 2. Adjust tension: Tighten the nut gradually until the chain has about 1/4 inch of sag at the midpoint between the sprocket and trolley when the door is closed.
• 3. Inspect sprocket: Check the drive sprocket for wear or wobble. Replace if teeth are sharp or uneven.
• 4. Test operation: Restore power and run the opener. Listen for reduced slapping. Readjust slightly if needed.