Auto Service World
Feature   January 1, 2008   by Andrew Ross

CounterTalk – Knowledge Building: Ford Triton Spark Plug Thread Repair

You would think that with all the resources that automakers have at their disposal, the products they build would be immune from peculiar failures. That this is not the case is no news to anyone in the automotive aftermarket (or among automakers, for that matter).

Whether it is as the result of unforeseen field conditions, a decision to let a small failure probability go to production, or an honest-to-goodness oversight, things do happen.

Who can forget the Ford 3.8 head gasket fiasco that saw the eventual replacement of thousands upon thousands of gaskets, a great many of them at the consumer’s cost?

So it was with that Ford legacy in mind that reports of the Triton spark plug failures trickled across my desk.

Here, in short, is the problem: every now and then, the owner of a vehicle equipped with one of the Ford Triton 4.6, 5.4, or 6.8 litre engines hears a bit of a ticking or tapping noise. Shortly thereafter, a spark plug tears itself out of its hole–in some cases leaving behind a broken ignition coil, and almost always leaving behind a steaming customer.

While there seems to be little agreement on the exact cause–suggestions range from failure to lubricate the threads periodically to the use of non-Motorcraft or Autolite plugs–most supposition has settled on a combination of a low torque specification (only 12 lbs.-ft.) and the fact that only four threads are used to secure the plugs.

Repairs have been in the works for some time, and a number of kits and companies are out there focusing on the repair. In addition to the Lock-NStitch system approved by Ford for repairs on 5.4L and 6.8L Triton engines, other types of systems include one by Time-Sert (which has its procedure on video at; a Fix-A-Thread/Recoil brand by Alcoa kit, fitting due to the need for aluminum; the Calvan 38900 kit; and companies that specialize in providing the required service. (Possibly the one with the best name is the California-based Blownoutsparkplug company.)

Lock-N-Stitch president Gary Reed says that the problems surrounding the fix are twofold. Both relate to the fact that the Triton uses aluminum cylinder heads. As a result of the different thermal expansion rates between the aluminum cylinder heads and their steel inserts, the inserts have been known to come loose, Reed says, causing a repeat performance of the incredible flying spark plug show.

Less dramatic, but just as troubling, is the fact that the different thermal transfer properties of steel affect the heat range of the spark plug. Since the steel transfers heat more slowly than aluminum–a situation that can be exacerbated if the steel insert loses contact with the aluminum due to incompatible thermal expansion rates, as explained above–the plug runs hotter than prescribed, and does not cool properly between firing sequences. This can lead to detonation and preignition problems.

The installation of the proper insert will retain the heat transfer properties of the aluminum and allow for a greater torque value to be used.

In any case, here are the highlights of the fix. It helps if you are familiar with spark plug thread repair procedures; I won’t cover every single step in the procedure. I have included points that should serve to illustrate why you shouldn’t wing it, however.

The repairs can be performed “in frame,” but if they are, special care has to be taken to ensure that the valves are closed in the cylinder being worked on, and thread areas are lubricated to keep metal chips from falling into the cylinder. It is also advised, by all sources I could find on the Web, to use a vacuum to clean out any cutting debris.

Probably the key point, and one that the folks at Lock-NStitch are quite proud of, is a special gauge the firm created to precisely determine which of the three cylinder head types is being worked on. The three types are distinguished by the profile of the spark plug seat.

Cylinder Head Types

( General Guide Only. Some Production Variations Exist)

Model Years Engine Size # of Valves

Type 1

‘ 93 to ‘ 00 4.6L 2V

‘ 93 to ‘ 96 4.6L 4V

‘ 94 to ‘ 00 5.4L 2V

‘ 94 to ‘ 00 6.8L 2V

Type 2

‘ 96 to ‘ 05 4.6L 4V

‘ 97 to ‘ 05 4.6L 2V

‘ 98 to ‘ 05 5.4L 4V

Type 3

‘ 02 to ‘ 05 4.6L 2V

‘ 00 to ‘ 05 5.4L 2V

‘ 00 to ‘ 05 6.8L 2V

The Lock-N-Stitch procedure also asks you to clean and measure the depth of the damaged spark plug hole using the gauge. (The gauge, locked to this depth, will be used again after the thread insert has been installed.)

After having determined the cylinder head types, machining of the damaged thread areas must be conducted.

To prepare the hole, slide the counterbore cutter into the well and use a 5/8″ socket with a long extension to turn the cutter. Apply cutting fluid. The cutter will cut a small amount of aluminum around the spark plug hole to allow the thread insert to be installed to the correct depth. The cutter cannot cut too deeply. Keep turning until it stops cutting. Repeat the process two times to make sure it stops cutting.

Note: If procedure is being done in frame, pack the flutes with bearing grease as a lubricant and to capture most of the chips.

Lock-N-Stitch has a drill bore alignment tool as part of its kit. The plug well on these engines is too deep to see into, so it is important to pay special attention to alignment in all procedures.

There are slightly different procedures for two-valve and four-valve heads due to the depth of the four-valve plug hole, but other than the need for extensions, the drilling-out and tapping procedures of the spark plug hole are generally similar to standard methods of spark plug thread inserts.

Anti-seize compound should be used on the threads of the installation tool to prevent the thread locker used on the thread insert from getting between the tool and the insert. The one-piece, hard-anodized thread inserts require a continuous installation motion to prevent the thread-locking compound from setting up before the inserts are completely seated. The insert is then tightened to 27 lbs.-ft.

(These thread inserts use a locking pin; a hole must be drilled in the thread area to locate this pin. A special provision is made for this in the insert installation tool.)

The last procedure is to retrieve the spark plug hole gauge used at the beginning of the procedure to determine that the insert is installed at the correct depth.

If the insert depth doesn’t check out, the locking pin can be drilled out, heat applied to the insert, and the insert removed prior to re-tapping the hole to the proper depth.

Once the insert is installed properly and to the proper depth, the spark plug can be installed. The company advises the use of only a “full-threaded” spark plug, and torquing it to 25 lbs.-ft.

For more information on repair procedures for Triton thread inserts, contact your supplier. Complete Lock-N-Stitch procedures are available at, or e-mail me at and I will e-mail you the manual and the Ford technical service bulletin.

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