Belt-Drive Opener Repair: what the visit covers

After a belt has been off the sprocket, the operator can end up out of phase: the motor thinks the door is somewhere the trolley is not. The symptom is a door that stops short at the top or the bottom no matter how the limits are adjusted, or a trolley that bangs into its stop bolt. The correction is part of every belt repair. With the belt lifted off the sprocket, the operator is run until the sprocket settles at its closed position; the belt is refitted with the trolley at the closed end; then travel and force are relearned so motor and trolley agree again.

How tight is tight enough

Belt tension is measured, not guessed. At the inner trolley a threaded shaft carries a coil spring and a square nut; turning the nut draws the belt tighter and compresses the spring, and the maker states the spring length that means the belt is right, roughly the width of a thumb. The technician checks that length, presses the belt at mid-span for a little give, and watches it run. A belt hanging below the rail is loose and will skip teeth. A belt pulled drum-tight makes sprocket noise, loads the motor bearings and wears the idler pulley. Both are corrected on the spot, and an adjuster wound to its end tells the technician the belt has stretched past saving.

Gear and sprocket at the motor head

When the shavings on the housing say the drive gear has stripped, the head unit's cover comes off and the gear-and-sprocket kit is replaced as a set. The belt is lifted off the sprocket, the old sprocket shaft and worm gear are withdrawn from the housing, the new gear is greased with the light grease the maker names and fitted with its bushings, and the sprocket is set back on top. The technician checks the motor shaft's end play, since too much play is often why the gear stripped in the first place. The belt is refitted, tensioned and phased, and the operator is run to confirm the sprocket turns true and quiet.

How to check the belt by eye

You leave knowing what a healthy belt looks like from the garage floor. It runs level, just above or inside the rail, with no visible sag between the motor head and the header. Its teeth are even along the whole length and its edges are square, not fuzzy. Every few months, with the door closed, glance up and along the rail; then open the door and look again, since sag shows on the return run. If the belt begins to hang below the rail, slap on the way up or click at the same point each cycle, that is the moment to call, while it is a tension adjustment rather than a stalled door.