Never make changes right before an event.
Last weekend I swapped a modern compact crank for a period-correct Sugino Mighty on my Nishiki Pro. I took it out on a 40 mile ride and all was well. Yesterday I went out again, and after a while I started hearing a creaking noise from the drivetrain. I looked down and the left crank arm is loose, and when I stopped, the bolt was gone. Bad, for sure, but worse if it had come off. I was stopped at the entrance to a gravel quarry & found a smooth baseball sized river rock, picked up a piece of cardboard from roadside trash (thanks, local rednecks) to use as a cushion, and tapped the crank arm in place. I one-legged it 8 miles back to the second-closest LBS (my favorite), got a new bolt, and used their shop wrench to tighten it. About 2 miles from home it had loosened again and I one-legged it home.
I've been riding and servicing square taper cranks since 1975, including a couple of years during college working at the LBS, have never used a torque wrench on a vintage bike and never had a crank come loose like this. I understand the science of why it's nearly always the left arm that loosens, but the torque wrench in my elbow that says "that's about right" has served me well up to now.
This crankset is one of the most-used square taper ones I own and I'm sure it was removed and reinstalled several times to service the bottom bracket or move to a different bike, but has been unused for about 20 years. The crank arm doesn't appear to be galled or deformed. I have a micrometer/click-type torque wrench that I use for my modern bike and other things. Park Tool says torque the crank bolt to 300-450 in-lbs. I've reinstalled the crank and torqued both sides to the Park Tool spec, and that's noticeably more than my seat-of-the pants torque value. Lesson learned, I guess.
Now I'm concerned about taking the Nishiki to to Cambria, even for the short Piedras Blancas route I'm planning to ride, so I'm going to take a ride on it today and check the left arm every few miles. Any doubts and I'll change to another bike that would only need pedals changed.
gugie , I hope nothing like this never happened on your Super Course!