<VV> spark plug insert / cylinder pressure

[Andy Kinzelman]

Guys,A friend has a car that hadn't been run for several years.  After having gotten it running - after some miles it blew out a spark plug (I had been told earlier those threads were weak).  I put in a spark plug insert; then checked the cylinder pressures - that cylinder has zero compression.I don't think that the zero compression is due to the blown out plug, nor the thread insert.  Nor do I think there had been a ring issue or holed piston beforehand (no oil burning or on the plug).
Is it possible one of the valves had been stuck only slightly open - so the engine would run without the piston hitting the valve - or is it more likely a bigger problem?
Please reply to this e-mail; my normal one (and VV-digest) is currently inaccessible.
Thanks,Andy KWisconsin