Seems to me the spanner v hammer and punch debate falls into two camps. So I’d like to conclude my input with the following observations.
Firstly, the brevity of my comment about disagreeing with SRM may have seemed a little pompous. Those who know me will vouch that of my many vices, arrogance or pomposity do not feature. Maybe I was a bit short because I get irritated when people take the view that because a company is well-known or big, it is automatically right.
I have known the Ford motor company to be wrong when it advised a certain piston / liner pairing that were actually a mismatch. I could give many similar examples - no-one has a monopoly on wisdom. It happens I am an engineer, and I do disagree with a 65ftlb torqueing of the mainshaft nut but, having said that, I also appreciate there are people on this forum who know more than I. Here’s why I disagree with using a spanner:
1. Accepted wisdom from those who built them originally is that a hammer and punch is superior to a spanner. Why go against that advice?
2. When using a punch there is no need to lock the engine. With a spanner there is, but how? Remember, if restraining the shaft with the sprocket, the cush-drive cam will be forcing against the nut you are trying to tighten.
3. If using a spanner, what torque do you apply? We know that nut has to be TIGHT, so why choose a figure that is only around half that of the industry-recommended torque for a nut of that size?
Would be interesting to know whether those who are experiencing failures are using a spanner or a punch. I will continue using the latter, as in over fifty years of fettling BSA’s I’ve never had a mainshaft nut come loose.