You'd think BMW would have learned a lesson about the small diameter shaft with a threaded stud instead of a tapped hole after the great airhead cam nose debacle. A whole lot of those poor things have been reefed on and snapped clean off.
For what it's worth, I just did this job and learned a lesson. Although my pump has the later style shaft with a tapped hole, the procedure is the same either way. I used the new seal which is common to all brick K bikes and I found it very easy to install flush using a large socket. Installing the shaft was also easy by drawing it through the seal with bolt and washer. But I somehow missed the fact that the old style cast impeller is not suitable for use with the new seal. Installing it will compress and ruin the seal and you have to start all over. The impeller is not the correct depth for the new style seal, and after you tighten the bolt/nut, you will find that the shaft is now locked up tight.
So, make sure you have the newer style stamped steel impeller and its required spacer to use with the current water seal.
Don't forget the oil seal behind the water seal, and the small o-ring for the drive gear shaft end, the bigger red o-ring for the coolant passage, and I thought it was worthwhile to renew the crush washers on the relief valve and temp/pressure senders or plugs while I was in there. No more leaks!
