The LiftMaster 71-1550B40LGH Sprocket Kit is a drive sprocket assembly for chain-driven LiftMaster operators. Built around a 50B40 sprocket, it features a 1 inch keyed bore with a 1/4 inch keyway, making it a direct, like-for-like replacement where a 40-tooth ANSI #50 chain sprocket is specified. In a typical overhead door or slide gate operator, this component mounts on the shaft and engages the #50 roller chain to transmit motor torque, restoring smooth, dependable operation when a worn or damaged sprocket needs replacement. It’s a practical service part for commercial and industrial LiftMaster door and gate systems that utilize #50 chain drives and a 1 inch shaft with a 1/4 inch key.
For correct application, confirm the tooth count (40), chain standard (#50), bore (1 inch), and keyway (1/4 inch) match your existing drive configuration. Installation should be performed by a qualified technician following the LiftMaster service manual: de-energize and lock out the operator, remove the old sprocket, fit the new sprocket with the proper key, align it with the mating sprocket, set chain tension, tighten the setscrews as specified, and reinstall all guards before testing. Using the proper sprocket geometry helps maintain chain alignment and reduces premature wear, supporting reliable operation in replacement, repair, or upgrade scenarios where a 50B40, 1 inch bore, 1/4 inch key sprocket is required.