Our spark plug repair kits are considered "Over the fender" meaning you do not have
to remove the head for spark plug thread repair.

stripped spark plug threads repair, spark plug thread repair, stripped threads spark plug.
The following instructions for kit part numbers 4412 and 4412E.


1. Wrench
2. Step-Tap
3. Insert Driver
4. Seat Cutter

Inserts sold separately

Cutting tools may shatter if broken. The wearing of safety glasses is required in the vicinity of their use.

  1. Start the step tap into the hole to be repaired keeping as straight as possible.
  1. Use the wrench provided, place wrench over tap and tap new threads. Continue to tap through until the cutting edges are approximately 1/4 inch below surface.

    Leaving the tap 1/4 inch below the surface ensures that the seat cutter will not hit the back of the tap flutes.
  1. Leave the step tap in the hole. Place the seat cutter over the shank.

    The seat cutter does two operations. First the seat cutter will cut the countersink for the flange of the insert, then it cuts a new seat for the sparkplug washer.

    This operation is the same for the taper seat inserts.

4. Using the wrench rotate the seat cutter. After a few turns lift the seat cutter to inspect the seat. Repeat operation until the seat is completely cleaned up. Remove the step tap from the hole. Detailed note:
Good Seat Complete
Bad Seat
1/2 incomplete
  1. Make sure the hole is clean and dry. Lubricate the driver tool with Time-Sert driver oil. Screw the insert onto the prepared hole.

    If doing deep hole repairs:
    Lubricate the driver tool with Time-Sert driver oil or 30wt Oil. Screw the insert onto the driver then into the prepared hole.
  1. Using the wrench provided rotate the driver into the insert. When the insert is seated the driver will tighten up. With increased pressure continue to rotate the driver through the insert until it loosens up. Then back the driver tool out of the insert.

    Note: Taper seat inserts
    These inserts are silver plated and require sealer p/n 6020 on the outside of the insert.
- Section View -
  1. Repair is complete. Solid steel threads are square to the reconditioned seat, insuring a good spark plug seal.