Spark Plug Thread Repair Do’s and Don'ts

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.

1. Don’t resort to using a parts store repair. Yeah, parts stores have repairs readily available but in our experience they are just temporary repairs that end up making holes bigger. Then an oversize repair is needed to clean up the mess. Parts store kits that commonly fail are Dorman, Helicoil and Save- Thread. Any that include “self tapping” or striking from the top are likely to fail sooner rather than later. If you’ve already used one of the temporary kits we most likely can still help.
2. Don’t work on the spark plug hole without first making sure the valves are closed. Open valves can be damaged by tooling and when blowing shavings out, open valves can allow debris further into the engine.
3. Don’t use anti-seize on the spark plug. Using anti seize will affect the torque specs because the plug will turn much easier.
4. Don’t accept an opinion from a shop that the cylinder head must be changed without checking with us. We’ve been selling these kits that have worked to repair rather large holes successfully. Occasionally holes will be too big because a Dorman repair has leaked compression out along the side of the repair eroding an oblong shape that’s too big. But this is usually not the case. Our repair options are available in oversize and are considered a permanent repair which have stronger threads than the original.
5. Don’t just try using a thread chaser when a spark plug blows out. There has to be enough material to chase (or tap) and the simple fact that the spark plug blew out indicates there’s damage already done and material missing. After a plug blows out, chasing the threads and re-installing almost always ends up in a repeat blowout.
6. Don’t drive the vehicle with a spark plug blowout or with leaking compression from a parts store insert. More damage can possibly be done. In emergency situations we have heard of driving short distances without a plug if the coil and injector for that cylinder is unplugged. This should be avoided if at all possible.

Do this.

1. Check with us before throwing in the towel. We have different options depending on the application and what’s been done previously. We have oversize repairs available that can fix rather large holes.
2. Read instructions carefully before doing the job. We also include extra tips upon request when purchasing certain kits from us.
3. Have all tools needed before starting the job. An air compressor, an air ratchet, an air blower and the usual mechanics tools. Also have a good light handy. Brake clean is helpful in carrying out shavings. Remember to change the oil afterwards in case some brake clean goes past the rings and into the crankcase. We have more suggestions included in our exclusive tips provided when you write “Tips” at checkout, or on the phone mention that you’d like to receive our free tips. See the kits below if working on a 2V 4.6, 5.4 or 6.8 Ford.
4. Contact us for choosing the correct kit if you're unsure.

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.