Drilling

Step 1 – Clear damaged threads

Insert the correct size drill bit into a drill and clear the damaged threads. Some specialised spark plug coiled insert kits will include a specialised tap which does not require drilling beforehand.

Tapping

Step 2 – Rotate STI tap into hole

Rotate the STI tap into the hole using either a tap wrench, suitable installation tool or spanner. It is often recommended to use a suitable lubricant during this process.

The tap is rotated clockwise, but may occasionally require a quarter turn backwards to free the debris and ensure a smooth completion.

Step 3 – Choose option

For slot-on installation tools…

….the insert should be placed on to the tool (tang upwards) and then the tang should be rotated so it falls into the slot. If available, an adjustable loop can be moved to line up the insert.

For thread-on installation tools….

…the insert should be wound onto the tool (tang upwards). There is often a catch at the end of thread-on installation tools which catches the tang and secures the insert in place for threading.

Installation

Step 4 – Install insert

To install the insert, place the installation tool with insert at the mouth of the newly tapped hole. Rotate the tool in a clockwise direction until the insert begins to take, then continue the rotation with a slight pressure until the insert is half a turn below the surface.

Step 5 – Choose option

Option 1:

To remove the slot-on installation tool…simply pull out. Do not rotate the tool anti-clockwise as this may cause the tang to break off prematurely.

Option 2:

To remove the thread-on installation tool, rotate anti-clockwise until the tool is free. The insert remains in the hole because the spring shape means that the insert can expand into the hole once the tang is free of the catch.

Tang removal

Step 6 – Remove tang

Use the tang removal tool, a screwdriver, or a similar long, thin object to snap off the tang. Simply place in the hole and apply a short burst of pressure until it snaps.