The coil is a little bit bigger than the threads, which will keep it in place when you're finished. 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. Now you can thread the appropriate-length coil over the installation mandrel. Mostly, you don't want any chips to find their way out the exhaust port and wind up in the catalytic converter. Street engines with a more normal compression ratio should be fine if you are careful, and blow the chips out with compressed air. I've also filled the cylinder (before tapping the hole) with oil-soaked clothesline to catch any chips - but that was in a racing engine with a squish band only a few thousandths of an inch deep.

Back out the chip-laden tap, and clean up any remaining chips. The chips will stick to the grease and come back out with the tap. To avoid getting aluminum chips in the cylinder when retapping the threads, you should coat the tap with grease. Continue threading the tap in to cut the new, oversize threads. This is to ensure the new threads are concentric and parallel with the originals. Start by threading the special Helicoil tap into the remaining threads in the head. Any readers out there who wish to attempt it might want to practice a couple of times on scrap parts. Warning: Installing a Helicoil or other threaded insert looks simple - but it's not. And that includes cast-iron, steel and aluminum parts. This type of repair can be used for almost any threaded fastener, by the way. (I pull and inspect plugs every couple of years and reinstall them with a small dab of antiseize compound, but that's another column.)Ī proper thread repair should last as long as the life of the car. 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'd give your mechanic a shot at fixing the threads before I held his feet to the fire. There are several types of repair inserts, but we prefer Helicoils. Or, as illustrated, you can insert a Helicoil. In fact, it may be possible to simply chase the old threads with a tap and clean them up. Thoughts?Ī: There are a number of ways to repair stripped threads. The mechanic said he could repair the threads, but my uncle says the cylinder head is ruined and the mechanic should replace it at his expense. The car was towed to the shop where I'd had a tuneup the day before - which included changing the spark plugs. Q: Yesterday I was driving home and a spark plug blew right out of the cylinder head.

Fortunately, it's possible to repair damaged threads instead of scrapping the head. Thank you for all the input guys its nice the see the community is so willing to help.Spark plugs that haven't been changed for a long time can become one with the cylinder head. I screwed in the new plug and reconnected the coil, etc and she was up and running again. My dad and i used a magnet to remove a couple of small metal shavings produced by the easy-out. But after all that i finally removed the rest of the plug from the engine. The easy-out was no picnic though, i had to ghetto-rig it up to some socket extensions and then use an adjustable wrench to turn it. Then, with a big pop i finally loosened it up and removed it from the engine. So i proceeded to use an easy-out to remove the threaded section, and at first it wasnt budging. What ended up happening was that it bonded to the rest of the porcelin/ceramic insulator and pulled it out. Nelsito65's idea actually came to my mind so i ran to the store, grabbed some epoxy and tried my best to get the spark plug to fit in where it originally was and hope the epoxy would make a strong enough bond so i could take out the threaded section. I would have just used an easy-out first but a piece of the insulator was still sitting in there (and wouldnt come out) and i didnt feel like drilling into that and getting it into the cylinder.

Ok sorry i havent updated in a few days, been quite busy.

Square easy out spark plug