See full version: How to Rethread a Spark Plug Hole
Run a commercially-available spark plug "thread chaser" tap of the correct size into the existing damaged spark plug threads and try to clean them up. If the damage isn't too extensive, maybe you'll get lucky and additional options will not be required.
Thread the tap into what remains of the existing spark plug threads, cutting new, oversize threads as you turn the tap increasingly tighter. Back the tap out after you have threaded to a depth equivalent to the threads on your spark plug. here
Install the spark plug into the threaded insert and tighten.
Purchase a threaded insert kit and install the insert into the spark plug hole if the threads are too damaged for repair with a thread chaser. A typical commercially-available threaded insert kit includes an oversized threaded tap, a threaded insert, and an installation mandrel. more
A: There are a number of ways to repair stripped threads. In fact, it may be possible to simply chase the old threads with a tap and clean them up. Or, as illustrated, you can insert a Helicoil. There are several types of repair inserts, but we prefer Helicoils. I'd give your mechanic a shot at fixing the threads before I held his feet to the fire. When a spark plug has had a chance to marry a cylinder head for 100,000 miles, it's not uncommon for the aluminum threads to come out of the head with the plug. (I pull and inspect plugs every couple of years and reinstall them with a small dab of antiseize compound, but that's another column.)
Start by threading the special Helicoil tap into the remaining threads in the head. This is to ensure the new threads are concentric and parallel with the originals. Continue threading the tap in to cut the new, oversize threads. To avoid getting aluminum chips in the cylinder when retapping the threads, you should coat the tap with grease. The chips will stick to the grease and come back out with the tap. Back out the chip-laden tap, and clean up any remaining chips. here
Now you can thread the appropriate-length coil over the installation mandrel. There's a raised flat on the mandrel that will catch on the tang in the coil, allowing you to thread the coil into your new threads. The coil is a little bit bigger than the threads, which will keep it in place when you're finished. The tang will pull the coil into place from the inner end. Once the coil is in place, remove the mandrel.
A proper thread repair should last as long as the life of the car. This type of repair can be used for almost any threaded fastener, by the way. And that includes cast-iron, steel and aluminum parts. Warning: Installing a Helicoil or other threaded insert looks simple -- but it's not. Any readers out there who wish to attempt it might want to practice a couple of times on scrap parts. more
Q: Will a wire type (Helicoil) insert work?
A: NO. The tip on the end of the wire insert is designed to break off after installation. The tip can lodge itself next to the piston rings and destroy the cylinder wall. We have also seen the wire insert melt down and then start leaking. There is also no reliable way for the seating surface of the spark plug to seal against the cylinder head.
Q: Can I drive with a blown plug to bring my vehicle in for repair?
A: Of course I do not recommend it. But I have had many customers remove the damaged coil, spark plug, and disconnect the fuel injector to drive the vehicle in for repairs. One customer drove his V8 over 700 miles to our location for repairs. Note! If you plan on following this process, VERIFY that you disconnected the correct injector.
Q: Is there a way to prevent this from happening in the first place?
A: Yes, we have developed a process that includes an inspection of the spark plug holes and a customized process for replacement of the spark plugs. Click here for more information more
The main improvement to spark plugs over the years has been the use of more durable metals in the contacts. A standard spark plug uses an ordinary nickel alloy steel for it’s contacts, and is typically good for 30,000 to 50,000 miles. Newer plugs use platinum inserts on one or both of the contacts, or iridium, or ruthenium, and can be good for more than 100,000 miles. The main advantage of the newer types is that they last longer; there is usually no difference to engine performance or miles per gallon. more
If the vehicle uses a cap and rotor those are usually replaced on the same schedule as the spark plugs, and then they’re all replaced together as a “tune-up”, usually with a bundled price. Very few vehicles use a cap and rotor these days though. here
It’s also very common for spark plugs to be done at a service interval where other things need done as well, such as intake system cleaning, transmission services and so forth. At a dealership there is often a bundled-cost service, while other service facilities will separate out the costs. For the most part there isn’t a cost savings to one way over the other, and the more important thing is just to stick to a regular maintenance schedule regardless of who does the work. here
Possibly, but it could also run worse. Many engines are very particular about what plugs they require, and can have misfires or run rough if they don’t have the recommended plugs. Most shops will prefer to install only OE plugs, or plugs as close to OE as possible for that reason.