PRO-LEVEL SPARK PLUG THREAD REPAIR (Part 2)

Thank you very much. The DOHC 2.4L head in this 2001 PT Cruiser spit the No. 1 spark plug without warning, taking the threads along for the ride. We suspect this resulted from poor thread quality coupled with a relatively low spark plug torque value. It appears that cylinder pressure worked its magic on the threads, finally causing the threads to fail.

Due to the over-chamber design, it's a long reach from the valve cover down to the plug threads. Removal of the valve cover allows better access.

Even with the cover removed (which requires removal of the intake manifold and coil pack), the plug threads are really buried down at the bottom of deep plug bores, so long tooling is needed to perform the job.

Goodson to the rescue. The spark plug repair kit (P/N FT-514LTK) includes everything needed to perform the fix. The kit is universal for a variety of heads, requiring only the proper-length inserts for any specific application. Inserts of all popular lengths are readily available.

In order to bore out the existing spark plug hole, the kit includes a long two-step reamer. The small nose indexes into the existing hole, while the larger-diameter cutters will increase hole diameter in preparation for tapping new threads.

The reamer is a healthy 9.017" long, which means that you won't struggle to clean out the entire depth of the plug hole. The pilot end diameter is 0.493" and the final reamer diameter is 0.640".

A handy centering adapter is slipped onto the reamer shank. This adapter is shouldered, allowing the lower portion to enter the top of the hole, while the adapter's larger diameter shoulder rests on top of the head. This allows centering alignment of the reamer to prevent the reamer from working at an off-angle.

While not needed in every situation, the kit's seat boring tool can be affixed to the reamer to cut a new seat to ensure that the thread insert's installation tool bottoms out, ensuring proper installation depth of the new insert.

Closeup of the reamer centering bushing.

Closeup of the seat cutter.

The inserts required for this job (P/N FFT-514125LA) feature a 14mm x 1.25 internal thread and an overall length of 1.00". The inserts are made of hard anodized aluminum instead of steel. This makes the inserts compatible with an aluminum head. The external threads feature a unique pitched thread made by Lock ‘n Stitch that creates a strong, no-back-out installation. The inserts include 1/16" locking pins, as well as added insurance against future insert back-out during any future spark plug service.

The aluminum thread inserts feature a built-in spark plug seat.

Once the damaged plug hole has been reamed out to size, a special Full-Torque cutting tap creates the threads that will accept the insert.

The insert installation tool features a small offset hole that allows drilling into the edge of the insert and its adjacent cylinder head wall material for installation of a locking dowel pin.

A guide tube provided in the kit inserts into the installation tool's offset hole. This allows use of the kit's 1/16" drill without fear of drill bit flexing and breakage.

This closeup shows the drill passing through the guide tube and tool, entering the top of the threaded insert.

The kit's anaerobic locking compound is applied to the external threads of the insert and to the 1/16" locking pin.

A special tapping fluid is also thoughtfully provided in the kit.

Even though we applied grease to the reamer to help prevent chips from entering the chamber, after reaming and tapping, we vacuumed any remaining aluminum chips using a shop vacuum, necked down to a 1/2" rubber hose that we inserted into the cylinder. We inspected the bore using a bore scope, assuring ourselves that all debris had been removed.

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