In an effort to allay fears about applying excessive torque, I tried to find my list of bolt torques for given diameters / steels. Couldn't find it, but did come across the following:
If I recall correctly, the diameter of the thread concerned is 3/4" and the torque for a nut of that diameter (fine thread) varies (depending on the quality of the steel) between 101 ftlbs for grade 1 to 480 ftlbs for grade 8.
I seem to racall those mainshafts were EN32 case-hardened, which has a tensile strength of 71,000 lbs / sq.in. That would put the torque required in midrange, well over 130.
In conclusion, the words of Bruce Main-Smith (from his Gold Star book) may be relevant, as the singles have a similar mainshaft.
"The precaution is to keep the nut really tight. And the penalty for neglect can be disentregation of the mainshaft. It is more effective to jar the nut tight with a hammer and brass punch than to heave on a spanner".