Removing sachs clutch nut
This is outlined in the manuals, but just in case you missed it. Removing and tightening the nut on the Sachs clutch is not straightforward as it moves the drive shaft. What you need to do is hold the shaft steady by holding the flat nut under the clutch nut with either a special tool or a wrench then torquing the clutch nut on top.
This is the tool made to hold the drive shaft in place.
This tool is available on a couple of the moped websites.
A cheaper solution is to simply use a 24 mm wrench to hold the flat nut in place while screwing on the nut.