The LiftMaster 71-1550B40LGH is the standard door sprocket kit for LiftMaster J (Logic 5.0) jackshaft and H (Logic 5.0) hoist operators on rolling steel doors. It's a 50B40 sprocket (for #50 roller chain, 40 teeth) with a 1 in. bore, 1/4 in. keyway and set screws. It mounts on the door's shaft and the operator's drive chain turns it.
Rolling steel or sectional?
LiftMaster uses a different tooth count for each door type on the J and H: 71-1550B40 sprockets (40 teeth) are for rolling steel doors and 71-1550B18 sprockets (18 teeth) are for sectional doors. This one is for rolling steel doors; for sectional doors use the 71-1550B18LGH.
Before ordering
- Measure the door shaft: this kit has a 1 in. bore with a 1/4 in. keyway.
- Replace a worn chain at the same time as a worn sprocket.
Turn off and lock out power before service, and support the door so it can't move.
Align the new sprocket with the operator's output sprocket, set chain tension per the operator manual and tighten the set screws on the key. Parts diagrams: J operator, H operator.
Specifications
| Sprocket | 50B40 (#50 chain, 40 teeth) |
| Bore | 1 in. |
| Keyway | 1/4 in. |
| Includes | Set screws |
| For | LiftMaster J and H (Logic 5.0) operators, rolling steel doors |
Compatible operators
| Operator | Door |
|---|---|
| LiftMaster J (Logic 5.0) industrial jackshaft | Rolling steel |
| LiftMaster H (Logic 5.0) hoist | Rolling steel |