This is the spline repair hub for the final drive on Airheads from 1970 to 1984. This part is made by Germany's leading manufacturer of aftermarket parts for BMW Airheads. This item is not available from BMW and will save you time and money when repairing worn splines.
This item is actually machined out of a solid piece of the correct material which ensures good spline strength, wear characteristics, and long life. These splines have been machined to the exact profile required to mesh with the drive coupling in the hub giving it the exact clearance required and minimum backlash; excess backlash accelerates wear. The repair process involves mounting the ring gear in a lathe and machining out the worn splined hub. The hole where the hub was removed is centered exactly with the ring gear center and is dimensioned to accept the repair hub. This ensures that when the hub is finally welded in place it is in true alignment with the ring gear center. The combination of the correct material and precise machining along with accurate positioning ensures a quality repair with maximum life.
The alternative method of final drive repair is to send off your unit and have someone weld in new material and then machine the splines out of that material. This can be a serviceable solution but the weld material will be variable in strength hand hardness. Reproducing the spline profile accurately is not impossible but more difficult than shaping a new one. It is often more expensive and time consuming than straight replacement with a repair hub.