Spark Plug Came Out

[RNajarian]

Hello Gang

Yesterday on a leisurely drive my 1983 SC turned into a VW. All of a sudden the normal growl of the 3.0 liter engine at 3000 RPM turned into the 4500 scream of an older VW Bug. It sounded like the muffler was removed. The car lost some power but for the most part ran normally. All indications from the gauges seemed normal except for a slightly higher RPM at idle.

When I got her home and let the engine cool I noticed that the Number Two Cylinder spark plug had completely worked itself out. There did not appear to be any damage to the plug.

Has this happened to anyone else? Any thoughts or concerns?

Thanks

RG Najarian

[stlrj]

Happened to my 67 VW bus.

[Mo_Gearhead]

I have seen it happen on other (domestic) engines, but it can happen on any gasoline engine.

If you (or your mechanic) failed to properly tighten the spark plug, vibration and cylinder pressures can make the plug walk/back out.

If the threads appear ok, just replace and properly tighten.

[Gunter]

I suggest to change oil now because while you were driving, the fuel was still injected in that cylinder without being ignited meaning: It washed down the cylinder walls and thinned out the oil.
Check the other plugs for being tight.

[3.2 CAB]

Another thing to check in addition to the possibility of your oil being fuel thinned, is there could also be damage to the last couple or so rings of the spark plug hole threads. The spark plug is under massive pressures at combustion, which seems to be the time that most spark plugs seem to get blown out the head. It might have damaged the threads inside the head. I have seen many plugs either back out of a head, and get blown out the rest of the way, and I have also seen spark plug failures, where the metal base, is tight inside the head, but all of the interior of the plug has been blown out of the base. There was just the lower threaded shell left in the engine. On a steel/iron head engine, generally just a new plug is all that is required for the repair, but on an aluminum head, there can be damage to the plug hole threads, that need to be repaired, BEFORE attempting to install a new spark plug, and possibly having threading problems, cross-threaded, stripped threads, etc.
Almost every time that I have been in or around an engine that has blown out a spark plug, it sometimes sounds like a shotgun going off, and scares the hell out of you, then it sounds like an air compressor gone wild, after that, till the engine is shut down. Good luck!! Tony.