Damn, how big was the nut?
Yeah, that was my first thought.
Co-worker of mine many years ago dropped a valve cover bolt into the intake port of a SBC while reassembling after a cam replacement. This was before he installed the intake. Instead of stopping and finding the bolt, he just got another bolt and finished up. Ran for a couple minutes before the bolt entered the chamber and --screech--, the engine came to an abrupt stop. Lucky for this kid it was an older pickup, he had that thing torn back apart in no time. In the end he tried to convince the boss he had dropped the bolt into the top of the head and it had gotten sucked through the PCV valve.:supp: Boss wasn't buying any of that fairy tale......... The only damage was a dent in the piston. Machine shop next door had a replacement in stock. Job was still finished by closing time.