How do you repair the spark plug thread on a 1990 Nissan pickup?

Answer 1

One of the most common DIY repairs for stripped cylinder head spark plug threads is a Heli-Coil or Perma-Coil spark plug thread repair kit. For the Nissan, it requires a size M14x1.25. These kits are available at most auto part stores and cost around $30. The kit comes with a tap, an insert tool, and several inserts. No drilling is required. You basically tap out the hole (lubricate the tap, hand start it, then use a socket wrench to tap hole full depth, clean chips from the hole). Then you select the correct insert to match the length of the spark plug threads. Coat the outside threads of the insert with hi-temp RTV silicone. Install the insert until it's flush with the top of spark plug threaded holes. You complete the installation by placing the swage tool into the insert and hitting it many times until the knurl expands. Finally, you install a new spark plug to the recommended torque. Wait till the sealant has set before running the engine.