Chain-Drive Opener Repair: getting ready

The chain hangs in a loop under the rail and slaps against it on every cycle. It used to sit snug. Now the whole house hears the door leave, and the sound has a metallic clatter it never had before.

Worth answering before the call

Is the trolley stuck at the very end of the rail, near the motor or near the door? Has anyone adjusted the limit or force screws, or run the opener with the chain off? Do the photo-eye sensors near the floor show steady lights?

Should I oil the chain?

Follow the opener's manual, and lean toward less. Many makers ask for the chain to be left dry or given only a very light treatment, because a heavily oiled chain collects grit that grinds the sprocket and drips onto the car. The grease that matters is white lithium on the rail where the trolley runs, renewed every two or three years, and on the gears inside the head, which the technician packs during a repair. Penetrating sprays are kept away from the whole drive.

Why does the door open only partway and stop?

Three causes account for most cases. The up travel limit has drifted short and needs turning out. The door has become heavy or stiff somewhere in its travel, so the operator senses resistance and stops, which points to the springs, rollers or track. Or the chain has slipped out of phase with the motor, in which case the limit screws have no effect and the chain must be re-set on the sprocket with the trolley at the closed position.