1949 B31 timing cam pinion

[DEDGE]

Hi All
Does anyone know if it's possible to change the timing cam pinion spindle (on a 1949 b31) without taking the engine out and splitting the crankcase.
I have a slight knock as the pressure is coming of the exhaust valve. Checked the valve push rods etc all ok, the timing cam pinon bushes seem to be the same size as the book say the new ones are so can only assume that the spindle itself is worn, No better with the inlet cam and all the drive teeth etc look ok. Any advice would be much appreciated.
All the best
Dedge