I am parting out a 1990 white miata, and spark plug #3 is badly stripped
at the part where the spark plug attaches to the socket, not the thread
that the spark plug itself goes into. The spark plug is completely
stripped, and the part of the plug that the spark plug wire boot
attaches to is broken off. The remaining part of the plug is too far
down in the narrow well to grab with any tools that I know of, and I am
afraid that a tap and die would just send pieces down into the engine.
I have never seen this before. Has anyone else had this occur and did
you find a solution? From what I can see, I am going to have to take off
the head and use vise grips to get the plug out.
It's not possible to grasp that plug with any vise grips I'm familiar with;
head on or off.
Stripping the hex on the spark plug isn't unheard of. The remedy is to grind
a bevel or chamfer around the end of the spark plug socket so that it can
reach lower in the spark plug well and grip what ever is left of the hex. If
the hex is truly and completely gone, a 20mm 12 point deep socket driven
over the remains of the plug might work.
Last resort, you could sacrifice a socket... Apply some JB Weld and let it
set over the plug until it dries. Never tried it, but it sounds reasonable
as long as you're careful not to "weld" the socket to the camshaft cover.
Guess I would try this as a last resort.
There is a type of socket that has a bunch of needles inside. These will
form around the damaged plug, and allow it to be removed. A big if is to get
the correct size that will fit in the well and around the plug. Otherwise,
the steel filled epoxy method sounds good. Since sockets are almost always
slightly oily driving the mess out afterwards should be reasonable.
Thanks for the responses, I will look for this needle socket and see if
it looks likely to do the job, otherwise I will go with the JB Weld
method. My main concern is that JB Weld is very drippy and takes a long
time to set up, so I would really need to protect the spark plug from
becoming permanenty attached to the engine, as was mentioned before by
Bryan. I will also try the 20mm socket first, but the hex on the spark
plug looks like it is truly gone, someone has tried to remove this
before I got to it.
There is a quick-set version of JB Weld, I'll probably try it first and
see if it holds on enough to break the spark plug free. I am thinking
about stuffing the area below the socket contact point with plastic wrap
or some other non-absorbent material. Any other suggestions on keeping
the bonding agent out of the spark plug threads/manifold area would be
Sacrificing a socket is no big deal, as I think that this is a good,
recently serviced engine that I can use in another miata or sell it if I
can get that plug out.
Thanks again and I will let you know if it works.
I think that what he is saying is to use oil (or wax) to keep the JB
Weld from bonding to the engine and spark plug threads. The instructions
on JB Weld say to apply to a clean, non-oily surface. That is probably
what he was referring to, not the condition of the tools themselves.
Wax, I never thought of that. It should be easy enough to drip some in
around the edge of the plug contact point with a candle and let it dry
before trying to bond the socket to the plug. I'll give it a shot this
But - the goal here is not to bond to the surface, the goal
is to create a form-to-fit socket around it. So wax/oil
that prevents the epoxy from permanently bonding to the
plug and/or socket (or even head casting) doesn't seem
to be problem at all, as long as the epoxy cures and
P.S. Good luck, Pat, hope you get it out...
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