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Stripped Spark Plug Thread

new 07/26/2004, updated 8/10/04

see also Stripped Spark Plug Hole

I sold my '99 BS to a friends son and replaced it with the car I welded with the blown #8 spark plug thread so now I have another challenge. As I recall someone on the list had done a helicoil on a V8, any advice?


I just had a though about this - since the plugs are 100K miles; perhaps, If there's enough thread left, I'll just bond the plug into the hole and worry about it at 218K.


To say that the platy plugs are 100k plugs is a pipedream. IMHO the factory plugs are MAYBE a 40k plug, the Super Double Platy's are maybe a 60 - 70k plug. Don't fool yourself and lose your motor. You WILL want those plugs out before 218k comes along.
I've had luck in tapping aluminum heads by rotating the engine until the piston is as high in the bore as possible with the exhaust valve still open. Then do your drilling - slow speed and good pressure on the bit to keep the chipcut in a continuous spiral that comes UP the drill bit. The drill will center itself in the pre-existing hole, just try to keep the chip from breaking. Next, get out the tap and pack it with grease. Cut about 2 turns and back out the tap. Clean out the chips and grease, repack the grease and continue. After cutting your threads - VACUUM out the combustion chamber. I use a small piece of clear hose attached to a crevice tool so I can SEE what I'm cleaning out. After Vacuuming, I blow air into the plughole at about 100 psi to clear anything else I can get to go out the open Exhaust valve. A bit of Aluminum in the catalytic converter is better than a bit in your rings. This procedure has worked for me a few times W/O biting me in the Arse.
Obviously, the BEST course of action is to take off the head....

Eric Lehmann
97 Ebony - welded
97 Toreador Red # 285 - welded
96 Willow Green # 326 - FUBAR No More! :-) welded
91 Jade Plus SHO-fa

IIRC on some of the early V8s it was an issue that one of the plugs was stripped. Seems to me it was the #5 plug.

Paul Nimz


AZ have a tool for $30.00 - combination piloted drill and tap uses solid inserts - comes with 3 different depths inserts. They also have helicoil but doesn't look as good.


I have checked out both types. The Helicoil and Insert type from Auto Zone. The helicoil is out of the question for the spark plug application. Because you have to break off a insert tab after install. The tab will end up inside the cylinder.

The insert type is not the right type of insert for our cars. The SHO uses The Ford Triton/Escort Style insert. http://www.timesert.com/FORD%20TRITON%20SPARK%20PLUG%20REPAIR.htm  If you did use the the fully threaded Auto Zone type insert. Even tho it does fit the Platinum plugs that most use. When installing the insert you can't tell how far into the cylinder the insert is. Because the insert does not have a bevel or seat on top IE will not bottom out. I want a permanent repair just shy of having the head reconditioned or replaced.



It was only a musing.

U are correct, better to do the job right. That's the way I was thinking it would go. Do I need to remove the cam cover to get closer to the plug well base? Someone also told me that there are helicoils that have built in vertical pegs these are used to drive in the coil and the insertion tool is used reversed to drive the pegs down locking the coil in, stopping it from rotating out. Anyone have experience of these?

Those are called Keen-serts.

Doug Lewis
Ford Performance Specialists Inc.

here is the kit I used. comes with the tap use the middle length one for our plugs. valve cover has to come off to get clearance for tap and socket. grease the tap lightly to pick up metal shavings. the get carried up and out by the tap. mine was done in June 2001.

Clare Allenby
 96 TR
London, ON


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