Steve,
The others who gave advice on cautiously working the plug out with
penetrating oil are good advice. By the way, an excellent penetrating oil
(if you can find it) that doesn't risk other problems is oil of wintergreen.
We used to use this when trying to free corroded/stuck fasteners on the
external hull of nuclear submarines. You had to keep it "soaked" (by adding
more as it soaks in) and the wait for a while (the longer the better,
sometimes like a day or two). An added benefit is that it smells really nice
(like peppermint).
After you get the old plug out, chase the threads with a proper size tap.
("Chase" means you carefully work the tap in/out/in/out etc. until you have
cleaned up the messed up thread(s) and use plenty of thread cutting lube).
This usually works quite well if the threads are in reasonably good shape
when you start out.
In the event you end up stripping the threads in the head, or they were
already stripped, there is a thread repair product called by the tradename
of "heli-coil". There are other manufacturers too. Basically, you drill out
the old bad threads and cut a new, larger diameter thread with a special
tool (comes in the kit) then thread in the insert and lock it in place. The
insert has an outer thread that fastens it into the head and an inner thread
that is of the proper spark plug size so you end up with a "practically good
as new" threaded hole.
Good luck.
Roy
'60 TR3a TS63103LO (in restoration)
techman@metrolink.net
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