Hi Rob, its been quite a while since I have had that part of my machine apart, but I think I remember the procedure...Here goes:
(1) Remove the 3 nuts and screws from the cutter clutch.This will split the clutch in two.
(2) Remove the 4 bolts that secure the engine to the frame and slide it off the machine to the right, with the right hand segment of the cutter clutch in situ.
(3) Slide the clutch outer complete with the clutch cone off the engine shaft.
(4) Slide off the cactus thrust pad and discard.
(5)slide on the new thrust pad.
(6) Check the cork clutch lining in the clutch outer and if badly worn, replace.
Reassembly is the reverse procedure.
(7) re-adjust the cutter clutch by use of the locking set screw at the bottom of the clutch fork, so that the clutch lever dis-engages the clutch correctly and the cylinder reel does not move.

Please let us know how you get on, Rob.
