I am replacing the shock absorber rubbers in my clutch but have not been able to put enough force/leverage on the clutch to compress the large rubbers. I was wondering if it is normal to need to put a lot of leverage to compress them or if sometimes the rubbers can be too big or stiff and I need to try a different supplier or cut them down.
You do need a tool with sufficient leverage to compress the big rubbers.
I can imagine that if you have old rubbers they may be harder than usual.
"NOS" rubbers are not very useable anymore after 70 years unless they have been stored correctly over the years which is not in the boxes of the usual autojumble seller but in a controlled atmosphere without sunlight.
It can be done by a single person but you really need the leverage.
Always use new rubbers.Set up the clutch hub on an old main shaft inserted in a vice.Use a large "C" wrench ( a big pipe wrench will work too) to put pressure on the hub to insert the rubbers.If you don't have an old main shaft, it will be very difficult to get those rubbers in.An old main-shaft for any Norton from the mid Thirties up to the Commando will work, so there's a lot to chose from. Good luck!