DennisB WiseAutoTools.com © Summary: Part of our ongoing effort to help make spark plug threads great again. Seriously, we specialize in thread repairs and this is a brief article on do's and don'ts in regard to spark plug thread repair. Spark plug threads in an engine can deteriorate when they’re loose due to vibration, resulting in a sparkplug blowout. Aluminum threads in the cylinder head can also be damaged if cross threaded or “seize” due to dislike metals. Ford 2V engines typically have the “spark plug blowout problem” and Ford 3V engines are notorious for having stuck spark plugs that can often break when removing them. Cylinder heads can sustain thread damage to the threads, even when following TSB procedures which call for working the plugs back and forth. Whatever the reason for repairing damaged spark plug threads, the following do’s and don’ts may just help complete the job with a long lasting repair. Don’t do this.
Do this.
TIME SERT 5553 - O.D. (Outside Diameter) of the Big Sert is .70 and this kit does repairs up to .66". TIME-SERT 5600 O.D. (Outside Diameter) of largest insert is .77". Time Sert 5600 has been used when Calvan failed due most likely because a thread adhesive was not used. Or was incorrectly applied. The largest the hole that this repairs is around .73. CAL-VAN 38900 This is a less expensive kit that can be used in many 4.6, 5.4 and 6.8 Liter engines. Insert measures .73". The lip measures .85" which can help seal in some cases. The largest hole that this is recommended for is around .68". Question - How do I use a spark plug thread repair kit I bought at Autozone? Answer - Short answer is don't. The thread repair kits purchased at Autozone and other parts stores are a temporary type repair. The tooling is too short and requires hitting the top of the insert in attempt to expand the top of the insert. When expansion and contracting occurs these inevitably loosen up and get ejected. Then a larger repair is needed. Question - How much does a spark plug thread repair cost? Answer - Spark plug thread repair costs vary lot depending on if a temporary type repair kit is used and if the work is done "DIY" or if a shop is paid to do the repair. It can run from $20 to $1,000. The average price of the permanent type kits that we sell for Ford 4.6, 5.4 and 6.8 engines range from a couple of hundred dollars to around five hundred. We have had many do it yourselfer's buy our permanent type repair kits and make repairs themselves successfully. They end up with a quality repair and save money by doing the work themselves. Question - How do I repair spark plug threads in a motorcycle? Answer - The procedure for repairing motorcycle spark plug threads is the same as on a truck or car. Basically ream, tap threads and install a bushing type insert. Then use a threaded installer to expand the bottom threads of the insert. Usually the size is either 10mm or 12mm and sometimes 14mm. Avoid the temporary kits and use a permanent type. More details on this on our Harley Davidson Spark Plug Thread Repair article. Question - How do I use a Helicoil thread repair kit? Answer - Usually Helicoil brand thread repair kits entail tapping threads, installing a wire coil or insert. If installing an insert the last step is striking the swedge type tool on top of the insert with a hammer! Read more in our Helicoil VS Time Sert article. Question - Do you have an over-size insert to fix the threads? Answer - Yes, we have options for bigger repairs that accept the original size spark plug. See the kits listed above for more info or give us a call for assistance in choosing the correct kit at 800-734-8665. Question - Is there a recall on Ford blowing out spark plugs? Answer - No. We've been selling repair kits since 2005 and there has never been a recall. Ford seems to have the worst problem with spark plug threads even though, all manufacturers use aluminum heads. Ford has revised the torque specification, increasing it to around 20 ft pounds, which may help reduce thread failures. However, there is no recall. The best fix is to use one of our proven thread repair kits which are considered permanent and have a great track record. The threads are upgraded to steel alloy which is much stronger than aluminum. More info can be found by visiting our main page on thread repair advice called Thread Repair Advice - Automotive Repair Articles by a Master Auto Tech. We've been selling specialty automotive tools including spark plug thread repair kits since 2005. Call for assistance in finding the best spark plug thread repair kit at 800-734-8665 x251 or provide us your details by using our Contact Form. Media Platforms Design TeamSpark plugs that haven't been changed for a long time can become one with the cylinder head. Fortunately, it's possible to repair damaged threads instead of scrapping the head. (Photograph by Chris Eckert / Studio D) Q: Yesterday I was driving home and a spark plug blew right out of the cylinder head. The car was towed to the shop where I'd had a tuneup the day before -- which included changing the spark plugs. 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 has about 100,000 miles. Thoughts? 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.) 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 From Popular MechanicsStart 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. 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. Street engines with a more normal compression ratio should be fine if you are careful, and blow the chips out with compressed air. Mostly, you don't want any chips to find their way out the exhaust port and wind up in the catalytic converter. 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. Now, use a pair of needle-nose pliers to break the tang off. It's prescored to break off cleanly and easily. Do NOT drop the tang into the cylinder! A few aluminum chips will not damage your engine, but a 1/2-in.-long piece of sharp stainless steel wire will tattoo the top of your piston and the combustion chamber before it finally gets out past the exhaust valve. |