I have been very impressed by this thread and have found it helpful,
a k1F and a k2f. For years I have been setting the timing by removing the center bolt that holds the points plate, and using a continuity light. ... While the method has always worked for me, the fact that I do not see it referenced anywhere makes me wonder if there is some reason, theoretical or otherwise, why I should not be using it.
Thanks very much for your comment. I'm happy to hear you're finding it helpful.
The center bolt performs two functions. One function is as an electrical conductor to connect the points to one side of the primary. That's why removing it lets you use a continuity light. Otherwise the ~0.5 Ohms of the primary would effectively "short out" the light, so it would be lit whether or not the points were open. The other function is to mechanically lock to points plate to the armature. What this means is that if
the points plate doesn't twist or move sideways by even 0.001" when the tension on the bolt is removed, the orientation of the armature when your light tells you the points open will be the same as when the bolt is retightened. Otherwise, it won't be, and the timing will be off.