Be very careful taking it off, not to disturb the valve timing.
From the Paul Friday files:
"Clutch, camshaft, oil pump, primary gears
This too was written by the omniscient Mike Whyte-Venables
Remove the clutch cable, and pull the connector off the oil pressure sensor. Remove the oil
filler/dipstick. Take the points cover off and remove all the bits, leaving just the bare shaft.
This shaft has a 22mm nut that is peened down into a slot in the shaft to lock it against rotation. Use
a very small chisel or narrow screwdriver to prise the dimpled bit up out of the groove.
Take a 22mm EXTENDED socket and a fairly long handle. Give the end a sharp whack or tug to
loosen the nut against the engine compression. The metal disk behind it may also come out if you
use your fingernails carefully.
Pull on the clutch arm to break the seal of the cover. Take a piece of wood, and tap the end of the
points shaft while pulling on the cover. You are persuading the bearing to slide off the shaft and
stay inside the cover. If you do not do this, the points shaft gear will come out of engagement with
the crankshaft gear, and you will have to re-time the engine. This is a good thing to avoid as it
involves much relaxation and at least a Sunday morning to re-time."