Sounds like the threads are stripped out.
Uncle Stan say have a steel incert installed.
I've seen them in many heads and they appear to be a good fix.

Stan Wilder

On Wed, 2 Jul 2003 08:07:22 -0700 Melissa Mourkas <westywoman@MAC.COM>
writes:
> I had to cut short a road trip yesterday because my 81 Vanagon has
> ejected
> the #3 spark plug twice during my travels, which I replaced by the
> side of
> the road with a new one each time.  I was able to tighten it down,
> or at
> least so I thought.  I called my mechanic from the road after the
> second
> occurrence and he assured me I could make it home safely and I did.
>
> Now that I am home, I am looking for wisdom from the list.  My
> mechanic says
> either I have stripped threads or a cracked head (horrors!), which
> is
> heating up, expanding and letting go of the spark plug.  I won't be
> taking
> the bus in until Monday, so any other thoughts, wisdom, advice and
> anything
> you all think I can check out on my own will be appreciated.  I have
> a few
> days off and time to tinker since I am no longer camping under the
> watchful
> eye of Mt. Shasta :-(
>
> Thanks!
> --
> Melissa Mourkas
> 81 Westy Basic Camper
>
>

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