<VV> Flying Sparkplug

[mvjacobi at comcast.net]

Well, my 63 Monza keeps showing me new and interesting tricks.  Last Monday night coming home, engine running smooth and quiet, suddenly sounded like an M-80 firecracker going off in the engine bay followed by a horrible racket sounding like a lost muffler or worse.  Arriving home in the garage, light revealed that the number one spark plug had departed it's hole and wound up in the battery tray.  A helicoil later and the plug was reinstalled and the sparkplug wire which had been caught up in the fan belt, replaced.  I can't for the life of me figure how that plug came loose.  Its been in there for at least three years.  Now suddenly it goes flying out!  Question:  Does the Vair have a reputation for spitting out sparkplugs spontaneously?  In the more than 55 years of driving various cars, this is the first time I have encountered flying sparkplugs from any of them.   With the plug back in its place, the engine is back to running smoothly, as if nothing untoward had ever happened.  Anyone have experience with this type problem?