Spark Plug Repair: How to Repair Stripped Spark Plug Threads

Spark plug repair can be done a number of ways. One reason a spark plug needs repair is because it is stripped and perhaps the reason for this is due to wear and tear. Spark plugs are parts of an internal combustion system that helps in firing up an air-gas combo to be able to start a vehicle. Repairing it may seem easy but if you are a novice with these things, you need to practice repairing scrap parts first before attempting it on your own vehicle. Better yet, if you have no experience in automotives it is best to leave it to the experts to avoid further damaging your vehicle.


Spark plug thread life when repair should last as long as the car is running and well. Some problems can be remedied by simply chasing the old threads with a tap and cleaning them. A Helicoil can be inserted as well. A number of repair inserts are available in the market today but most prefer the Helicoil. This is a type of thread insert fastener inserted into the cylinder to add an additional threaded hole.

Threading the Helicoil Tap

Mechanics would usually start by threading the Helicoil tap to the remainder of the spark plug threads. This is will make the new threads parallel to the old ones. They would continue to thread the tap to cut in to the new and oversized threads. They usually grease the tap to avoid aluminum chips to get into the cylinder as the process of re-tapping is taking place.

Threading the Installation Mandrel

After this procedure, the installation mandrel can now be threaded the right sized coil. The mandrel has an elevated flat that will snap on the tang in the coil that will allow the mechanic to thread the coil into newer threads. The coil will have a much bigger diameter than the threads. The tang will also function to pull the coil to its place from the end that is located inward. The mandrel can be removed as soon as the coil in placed in its position.

Tanging the Pliers

Lastly, a pair of needle nose pliers will be used to break the tang off. Usually they are already easily breakable. Avoid dropping the excess tang into the cylinder. Although, it won’t damage anything if aluminum chips fell into the engine but a piece longer than about ½ an inch can do so.

Test your engine as soon as the threading is done. This would usually fix the problem and if it doesn’t it simply means the problem could be deeper that a stripped spark plug. Always have a professional mechanic check car problems to avoid further damaging your car. This information is intended to be used as a reference only. Spark plugs are deep within the car’s engine and coincide with processes such as internal combustion so always take extra precaution when repairing spark plugs.