First off you need to remember that the nut uses a reverse thread and second make sure you use a torque wrench when you reassemble it to insure its not over tightened.
If you look at the top portion of the shaft you'll see the nut on top followed the gear then the shaft. You want to grasp the shaft just below the gear (where the gear sits against the shaft ) with a pair of pliers, small locking pliers etc etc.
If you disassemble the KIPS system remember that some manuals identify the sub-port valves incorrectly. There is a correction on the JustKDX web page in the Tech Tips section.