Barrie
You are absolutely right, i had completely forgotten about that retaining pin for the Weller spring, as you say it is good that it has good life, as you describe access is very difficult, whilst it has a 1/4 BSW thread , it has a taper to locate it which acts like a Morse taper which locks it in.
I remember removing it from my 1936 16/80 which had been dismantled for some time, it needed a bit more than a screwdriver to loosen & unscrew it as it was also corroded in!
I am afraid i had to move its position on my engines due to the larger main bearings also the flywheel boss diameter, in the process i redesigned it to a straight pin which has a 4BA female thread to enable it to be removed, then a 5/16 Grub screw to retain it!It is unlikely to be corroded in like the original!
You will appreciate i have the benefit of new parts for my engines & do not get involved in repair of the engines!
I wonder how many repaired engines have new Weller springs fitted?
Robin