Camshaft timing when the sprockets are ONE tooth off from straight up.
I was 16 and not very well experienced in automotive yet when my 1968 Ford Fairlane 500's 289 cube V8 engine started to run really hot one Friday night, and it was way down on power too. I had no clue what was wrong and continued to drive it through the evening, eventually I ended up at a buddy’s house partying.
Forgot about the car until the next morning when it wouldn't start. Got a hold of my brother and he came down to check it out, told me that the timing chain had jumped. "What the hell does that mean?" I asked, and he gave me a brief explanation of what I had to do to get it running again. I had a small 3/8 drive socket set and a few wrenches, plus my buddy had a few tools, and I bought a puller for under $20 bucks, which I still have 45 years later. Between the two of us we had it running again that afternoon. Not bad for a couple of young dumbass punks.
The nylon coating had cracked to pieces and allowed the chain to slip, but as long as the engine was still hot it would restart, likely from heat in the cylinders. That was the first of many experiences with nylon coated timing chain gears for me.