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Spark Plug Threads Damaged or Stripped – Repair Kits FAQ’s

Spark Plug Threads Damaged or Stripped – Repair Kits FAQ’s

DennisB © Summary: This auto repair article is on commonly asked questions about spark plug thread repair on Ford, Dodge, Mazda, motorcycles and really just about any application. We talk about competitive brands as well. We’ve sold millions of dollars worth of kits that have saved our customers hundreds of millions of dollars by fixing their stripped or otherwise damaged spark plug threads rather than scrapping expensive engine parts. Replacing a head could be a couple of thousand dollars compared to repairing threads with a quality kit runs $200 to 500. We cover the most asked questions below.

Parts Store Kits

Question – Can a spark plug hole be repaired after it’s had a part’s store thread repair kit fail already? The hole is bigger than it was before.

Answer – Yes. We help Ford owners and repair shops all the time fix previously repaired spark plug holes. Based on the calls we get, the little kits from parts stores don’t have a very good success rate. We offer several great options depending on the exact engine we’re dealing with. We sell a lot of Time Sert Big Sert kits, Calvan kits and we even sell Time Sert triple over size kits that put an insert inside another insert making it the largest outside diameter kit available on the market anywhere. And it still takes the original size spark plug, which is the M14x1.25.

Question – I have a 2002 Ford F150 and I need to know if the Calvan 38900 kit will work for my spark plug hole that was previously repaired with a Save A Thread kit?

Answer – The Calvan insert is .73 inches measuring on the outside of the threads. The kit comes with an 11/16″ reamer which is like a drill bit. So if you have an 11/16″ drill bit try it for size in the hole. If the hole is smaller than the drill bit, the 38900 kit will work.

Question – I’ve got a 2000 Ford Expedition and had an insert from Napa fail. The spark plug hole when checked with a drill bit, is larger than 11/16″. Is there another kit that will work to repair this or do I need a new cylinder head?

Answer – We have a larger kit available. The Time Sert 5600 has an insert with the outside measurement of .77 making it the largest one available.

Question – I have a 1999 Ford F250 with a 6.8 V-10. I bought a Dorman thread repair kit and it is too small for the hole. Do you have a kit that will work?

Answer – We’ve had a lot of customers say the Dorman thread repair kit, that uses the long 3V spark plug, didn’t work or only held for a short time. Our kits are a permanent repair not just a temporary fix. We have three kits that could be used for your application. The Time Sert 5553 and the Calvan 38900 are both oversize thread repair kits. The Time Sert 5553 kit works for many applications so a lot of repair shops purchase it because of the wider range of engines it can be used on. The Calvan kit will work for your truck and it has a has a little bigger outside diameter on those inserts and uses an 11/16″ reamer/drill bit before you tap threads. So checking the hole with an 11/16″ bit to make sure the hole is not too big can be done before ordering. If the hole is bigger than 11/16″ then we have the Time Sert 5600 which has an insert with outer diameter measuring on the outside of the threads of .77″.

Different Applications

Question – I have a Ford Explorer with a 5.0. Will the Calvan 38900 kit work for my engine?

Answer – No, the Calvan 38900 kit is for 4.6, 5.4 and 6.8 liter 2 valve SOHC (Single Over Head Cam) engines from around 1998 to most of 2004. The line up piece included in the kit is made to go down in the spark plug well. The 5.0 doesn’t have this design, the spark plug hole is near the surface. The Time Sert 5553 will work, because the tooling is different. The Time Sert 5553 has a smaller end on the tooling which is a stepped design that guides the tooling instead of a line-up adapter being used.

Question – I see a lot of spark plug thread repair kits for Ford 8 cylinders. How about a spark plug thread repair kit for my 2002 Dodge Caravan with a 3.3 Liter engine?

Answer – Yes we have kits that work for just about any make including 4, 6, 8 and 10 cylinder motors and some for motorcycles too. Your 2002 Dodge Caravan 3.3 6cyl. uses an M14x1.25 spark plug with a taper seat. The Calvan 38900 is NOT recommended because of the line-up tool will not work on your model, so you may end up drilling crooked. But the Time Sert 4412 or a 5553 uses tooling that has a smaller end which acts like a pilot centering and straightening the reamer. So the kit I recommend for your application is the 5553 if you’ve had a parts store brand fail and this is a second repair or the Time Sert 4412 if there’s never been a repair insert of any kind used previously.

Question – Which kit do I use for a first time repair for stripped threads on a 2000 Mazda Miata? I’m not sure what thread pitch.

Answer – The spark plug is an M14 with a 1.25 thread pitch and it has a washer seat. The kit is a Time Sert 4412. And there’s a 4412E which has longer tooling. The E stands for extended reach and this kit is easier to use when the spark lug is down in a well and not near the surface. These kits work on taper or washer seats but the inserts are different. We have shops that purchase washer and taper seat inserts to have on hand so they can do quick repairs when either come in their service bay. M14 is a the most common size used for automotive spark plugs. And the most common reach (or length) is 3/4″. The M14x1.25 with a washer seat that can be used on the Miata is the 44111. The M14x1.25 taper seat that we commonly sell is the 44187 and can be used on a lot of applications.

Access in the Vehicle

Question – There’s not much room to get to the back cylinder on my 2003 Ford F150 with a 5.4. Does the head have to come off to do the spark plug thread repair?

Answer – No. Using the Calvan or the Time Sert kit is an over the fender repair. It’s just a little more work than changing the spark plugs. So if you’ve ever changed the spark plugs, you know what’s required to gain access. When I work on these models I use bungee cords to help hold hoses and wiring out of the way. Sometimes the injector rail needs to be loosened so it can be moved slightly.

Valves Open or Closed

Question – Why is it important to make sure the valves are closed when doing a spark plug thread repair?

Answer – Tooling can sometimes hit the valves if they are not closed. Metal debris may also go throughout the engine as well, when blowing the cylinder out. Closing the valves isolates the cylinder and prevents the drill bit or reamer and the thread tap from hitting and bending or otherwise damaging the valves.

Question: How do you check to see if the valves are open or closed before doing a spark plug hole thread repair?

Answer: One method is having someone turn the engine over by hand with a ratchet and socket on the crank bolt and using your thumb to feel the pressure from the compression stroke when the piston goes up. Turning the engine a little past the end of the compression stroke the valves should be closed and the piston will be down. But, it’s not too easy to put your thumb over the spark plug hole if it’s 4-6 inches down in the spark plug well. So, one of the easiest ways is with our cylinder leak tester which is the 389-4000. See that video for more details. Another way is checking the valve position with the valve cover off. On OHV engines make sure valves on the cylinder being worked on is on the low part of the cam lobe and the valves are not being pushed open. I like the method that uses the 389-4000 the best because it’s easier and doesn’t required the removal of the valve cover.

Prevent Piston Damage

Question: How can I be sure that the piston is down far enough that drilling won’t damage it?

Answer: By following the previous step with the 389-4000, the piston should be down out of the way. You could also take a long screwdriver or long 1/4″ extension and stick it down the spark plug hole and feel the piston. I used this method to find top dead center on #1 when doing timing belts on some engines. If you can’t touch the piston it’s down out of the way. If you can touch it, you can take a measurement and compare the length to the tooling as a reference. You could even make a mark on the tooling with a sharpie if you want, just to be sure.

Repeat Spark Plug Blowout

Question: On my 2000 Ford F150 with a 5.4 Triton, I’ve had a repair shop install an insert and it failed and blew out a short time later. They say it’s time for a $2,000 head replacement. Do you have a thread repair kit that is oversize that I can use?

Answer – Yes. We have several options. The Time Sert 5553 is a Big Sert kit that uses oversize inserts kit that may work. The Calvan 38900 thread repair kit has the next largest size outside diameter insert. And finally, we have the Time Sert 5600 which is a triple oversize kit with the absolute largest outside diameter of any kit. ALL of these kits are the same inside diameter that takes the original size spark plug that the vehicle came with.

Extreme Mobile Repair

Question – I’ve read about a guy online that charges 800 dollars plus expenses to fly in and do the spark plug repairs. Is this really all that complicated of a repair?

Answer – No. We have very easy to use thread repair kits available. There’s absolutely no way I’d suggest to anyone that they should spend their hard earned money to fly someone in, all expenses paid, to install a spark plug thread insert. Since 2005, when we first started, we’ve sold our thread repair kits to many professional shops as well as do it yourself-ers that have performed permanent repairs quickly and dependably saving thousands of dollars compared to replacing the cylinder heads. With the money saved, I’m sure a lot of them used it for their own travel expenses… like maybe taking a family vacation.

Ford Specific Dealer Kit

Question – I’ve seen online that Ford uses a kit called Lock-N-Stitch. What do you think about this repair system?

Answer – Lock-N-Stitch kits are over priced in my opinion. They use aluminum for their repair insert for aluminum heads. Our spark plug thread repair kits come with steel alloy inserts which are much stronger than the aluminum threads in the head that the vehicle came with originally. Our inserts share enough of the same characteristics as the aluminum so there’s no issue with thermal expansion or heat transfer problems. The Lock-N-Stitch kit is also more difficult to use because of the extra step of installing a steel pin along side the insert to lock it in place. The Calvan insert has a shoulder at the top which allows it to tighten like a bolt does. The Big Sert thread repair kit we sell made by Time Sert uses a tiny locking pin that is embedded in the side of the insert. It requires no extra steps to install but provides extra “locking” power. The installation driver also expands the bottom of the insert locking it in place. Since Ford doesn’t warranty the Lock-N-Stitch repairs there’s really no advantage or need to spend extra money and go through the extra steps only to end up with the same weak aluminum threads. In fact many Ford Dealerships obviously agree because they purchase our thread repair kits and are repeat customers for more thread repair inserts. This includes both the Calvan brand and Time Sert brand.

Snap On Thread Repair Kit

Question – I have a FRT10 Snap On thread repair kit. Will the Calvan replacement inserts work? How about the Time Sert inserts?

Answer – The 389-100 inserts will work for the Snap On (Blue Point) kit because the Snap On and the Calvan kits are made by the same manufacturer, which is Horizon Tools. We have the inserts for a much lower price than if you bought them off the Snap On truck. The Time Sert inserts are a different brand and have a different outside diameter so they definitely will NOT work. We have replacement inserts for both Time Sert and Calvan kits but you have to stick with the correct brand.

The Best Brand

Question – Which is better the Calvan or Time Sert?

Answer – Calvan and Time Sert are two different brands, just like HP and Apple are different brands of computers. Each of them are good but do things differently. Calvan is limited as far as the application, whereas Time Sert has a very comprehensive application list which shows from the large number of kits and inserts that are offered.

Question – I have a 2006 Ford 3V engine that has damaged aluminum spark threads after removing broken plugs. Do you have a kit for my application?

Answer – Yes. We sell the Time Sert 3221 and the Calvan 39300. Both are designed to install inserts that replace the damaged spark plug threads for these engines. We’ve had Ford dealers purchase both brands.

Extra “How to” Tips

Question – I read in an article at DenLors Tools that free tips are provided when the Calvan 38900 is purchased. Does Wise Auto Tools provide these tips also?

Answer – Yes. We email the tips upon request when the Calvan 38900 is purchased. At either of our websites, just write the word “tips” in the comments when checking out and we will email so you have time to review them before the kit arrives.

Any questions not covered? Feel free to call Dennis at 800-734-8665.

19th Jul 2021 DennisB

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