We played an outdoor gig this afternoon. Everything was sounding great up to the end, then the sun started beating down on my NS...

3rd tune before the end, I start hearing really "tinny" string noise...and my sustain starts to disappear.

2nd to the last tune we played, I start playing, and there's nothing--I pluck, and the strings are instantly dead. I don't figure out what's happened until I push on the back of the neck with the palm of my hand, and suddenly I've got notes, volume, sustain back.

The neck changed just enough in the heat to bottom out the strings on the fretboard!

I got a hold of my truss rod wrench and loosened the rod a bit...and was able to play the last tune of the gig just fine.

Is my action *too* low? Anybody else have this happen?

Yeah,

Direct sun+low action = no sound.

But your action wasn't too low, the problem was the direct sun, it's hard on any instrument, but the difference in contrast will make anything go out of tune as least, and expand too.

Try playing a black plastic clarinet in direct sun (I used to in marching band back in school days). ouch!

I won't do an outdoor gig unless I'm going to be covered.

Greg,
covered as in "covered by a guarantee to play"?
Dave

ps some acts require money upfront and put the promoter in the hole before the concert,
hoping his/her ticket sales will cover the guarantee and also a profit.