Karl, if you get it really hot, the metal swells up and it doesn't want to rotate. This is very bad. The temp gauge won't show the overheat because steam, not water, is touching the sensor, and steam is a cruddy conductor of heat. It was a LOT hotter than it showed.

At a minimum, I would retorque the head bolts NOW, before I ran it again, and I bet several are loose..

It's not a lot of work, just frustrating to get at around the carb and brake booster and MC, and the stock clamps are the spring type and often just at the wrong orientation to get the pliers on them.