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Last Fall, I was winterising my equipment and I accidentally stripped the spark plug hole on my yard vacuum. Its a 31 year old machine and I didn't turn that hard, so its probably a failure that has been inching its way to happening for a while.

But no worries, this is a great opportunity for me to make a video about repairing stripped spark plug holes with helicoil type repairs. I used one of those to fix the brake rotor mount on my mountain bike and it worked great.

So the question is, does anyone have any specific suggestions for a specific kit (with links) that is good and that has everything you need in one kit. Including the drill bit UNLESS its a standard size bit. But I don't think it it, its probably bigger than 1/2" right? So the bit, the coil, the install tool, the thread tap etc.

I know I could also repair this by just replacing the head. But I'm making a video out of it so I really want to use a repair kit rather than a replacement head.

Here are two suggestions I have in my toolbox. Depending on how bad the thread are botched, will dictate which tool you need. If you purchase a kit, make sure it contains the proper length insert.


You can google search “spark plug thread repair kit” to find a kit which best meets your needs. Drill size I use is .500”.

What are the numbers on the engine.

I recommend removing the cylinder head.

You need to make sure you install the appropriate length insert to match the plug used in the engine.

Here is a good video:

l008com said:

Last Fall, I was winterising my equipment and I accidentally stripped the spark plug hole on my yard vacuum. Its a 31 year old machine and I didn't turn that hard, so its probably a failure that has been inching its way to happening for a while.

But no worries, this is a great opportunity for me to make a video about repairing stripped spark plug holes with helicoil type repairs. I used one of those to fix the brake rotor mount on my mountain bike and it worked great.

So the question is, does anyone have any specific suggestions for a specific kit (with links) that is good and that has everything you need in one kit. Including the drill bit UNLESS its a standard size bit. But I don't think it it, its probably bigger than 1/2" right? So the bit, the coil, the install tool, the thread tap etc.

I know I could also repair this by just replacing the head. But I'm making a video out of it so I really want to use a repair kit rather than a replacement head.

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Many times when removing spark plugs from customer engines, I find the plugs to be too loose. I think they are afraid of stripping it. Anyway, I have two engines with stripped spark plug threads and one engine with stripped carburetor bolt threads I will work on this winter. Occasionally people call about spark plug thread repair, but I don’t offer this option. Helicoil is a popular brand and holds up.

I've only used a helicoil once on an MTB brake caliper and it works really good. The only issue was that it was really hard to keep the tap perpendicular to the hole I was trying to thread. But I did get it eventually, thankfully. These carbon fiber frames are not cheap! But the way spark plug taps work, it should be even easier to do it right.

Now necessary is the thread sealer though? Wouldn't the kits come with it if it was really necessary?

I always use Lotite blue on any threadsert I install,

Isn't loctite just going to burn off after a few minutes of running the motor?

I’ve never had an insert come loose in my 50 years of experience.

spark plug helicoil repair kit

Honest Abe said:

spark plug helicoil repair kit

Home Page - Runnings

www.runnings.com

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Well those are hard to get started and causes a loose fitting. They are supposed to self feed but don't. I recently tried one on the Poulan with a strip plug hole. Almost never got it started and then kept wobbling around.

It is best to use a regular Heli Coil but those kits are expensive. And mainly only shops can justify the costs.

When we had our VW aircooled shop we used tons of helicoils for spark plugs/exhaust studs. Always a success. Used red loctite when installing. As a shop, we would buy starter kits for what was required and then just ordered extra inserts kits as required. Slowly built up to having all the common thread sizes. A few seldom used sizes we would buy a longer insert refills and just cut them to length instead of buying different lenghth refill kits.

That is the problem that cheap kit is not a Heli-coil version but is a threaded insert. Plus they are reaming the hole and then tapping it for the insert all in one operation. Next time I try the kit I brought I am going just drill the hole and they tapping it. But I am looking for regular Heli-coil tool sets for the 10, 12, and 14mm plugs. I know three different kits so that is around $400 to start with.

Have you seen this kit, had one in the last shop I worked in, before i retired. For M14 I used spark plug tool. https://www.vevor.com/home-tool-kit...MIpbm_3Y_6kAMV7lR_AB0u8Ra5EAQYCSABEgKZavD_BwE

Not even the right thread pitch.

I need M10-1.00, M12-1.25 and M14-1.25.

thread cert is more common in the air cooled world. The best fix is to make a video on replacing the head, or show someone how to properly remove the head, weld it, surface, and drill / tap a new plug hole. I would only use a heli-coil or thread cert on a head that was NLA used or new, or very expensive. Lots of the old mower engines from the 1990's are out there in masse as to used parts. Both thread certs and heli-coils can fail or be problematic when the plugs comes the next time the it is removed. So ask yourself why go thru all the hoops to remove and then repair it, then put the old one back when you could have a replacement ready to go.

What about these individual kits?

sgkent said:

thread cert is more common in the air cooled world. The best fix is to make a video on replacing the head, or show someone how to properly remove the head, weld it, surface, and drill / tap a new plug hole. I would only use a heli-coil or thread cert on a head that was NLA used or new, or very expensive. Lots of the old mower engines from the 1990's are out there in masse as to used parts. Both thread certs and heli-coils can fail or be problematic when the plugs comes the next time the it is removed. So ask yourself why go thru all the hoops to remove and then repair it, then put the old one back when you could have a replacement ready to go.

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Helicoils are normally very reliable long term if installed correctly. Who would go to the trouble of removing the cylinder head, welding it, tapping a new hole, probably have to replace head gasket, and reinstalling cylinder head? That sounds like something they would do in Pakistan.

At 3/8" that is only 9.5mm reach and I need something closer to 12.7mm reach on the 10mm plugs and both the 12mm and 14mm are way too short at 12.7mm (12mm) and 9.5mm (14mm). Both the 12mm and 14mm plugs I use here have a 19mm thread reach.

I found what I was looking for. By sure accident McMasters vendor sent me the wrong tap for a current project. Just a mix up on packaging but this time it is beneficial to me. There was enough info on the tap to lead me to a master Helicoil chart with kits, individual sets of Helicoils, and all the various installation tools. It even gave me the drill bit size for each. Even at $79 for a full installation tool kit is a heck a lot better than the one at McMasters for $354.

I believe the problem with the current kit on hand is simply that the holes needs to be pre-drilled instead of the tapping tool doing it. I should know later today provided don't start raining. My neighbor may have the bit I need. If I still come up with a loose fit then I only those inserts on tapered plugs. I rarely see tapered plugs here.

Either way I need a tax write-off so I be getting the regular Heli-coil kits. I can always trim the 1.5D coils to 1.25D size for the 10mm and 14mm and the 1.5D coils are fine for the 12mm plugs. That would give me 12.5 , 18, and 17.5mm coils for the 10, 12, and 14mm plugs respectively. Now the shorter 14mm plugs used in the old L heads (ie RJ19LM for example) does have a 9.5mm reach so that kit listed above would work fine as they are .68D coils.

Tiger Small Engine said:

Helicoils are normally very reliable long term if installed correctly. Who would go to the trouble of removing the cylinder head, welding it, tapping a new hole, probably have to replace head gasket, and reinstalling cylinder head? That sounds like something they would do in Pakistan.

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Huh? I was machinist in a well known high end racing and fleet machine shop once. I can't imagine any reputable mechanic letting drill and tap filings fall down into the cylinder to get caught in the cylinder and whiz around, or wedge the valves open a bit. THAT sounds like something from the third world or Bob's DIY Old Oak Tree Garage. I am out of this forum if that is the preferred method of repair. Frankly, I'd just get a good used head off Ebay from a seller with a 100% rating and 5,000 items, check it for warp and replace the head. Most heads are fairly easy to remove because small engines usually say in the manual to decarbonize them every so often.

Hi sgkent,

Don't take it personally.

Many who visit this site are only looking for the immediate "fix" to their dilemma, not a correct or permanent one.

Some of the suggestions make me laugh, but I don't take them personal.

Sgkent, how do you repair a stripped spark plug hole on a 2-cycle engine? Buy a short block? I’ve saved a lot of engines by installing a helicoil with no disassembly. To keep chips outside the cylinder I coat my tap with tons of grease and slowly run the tap into the hole. Don’t go too far in before backing out the tap, cleaning it, regreasing, and repeat. It may take a half dozen passes, but I don’t remember a time, but cheaper than a tear down. I always inform the customer of the odds of possible failure before attempting, but almost everyone is willing to take the chance. Only once I can remember where I failed.

Ever heard of grease? It catches nearly all of the shavings and in the case of aluminum rubbing alcohol. Now also on two cycles you just keep the piston above the intake port and use hi pressure air to blow out the shavings thru the exhaust port. What few left are discharged as you cycle the engine with the muffler still removed. Actually if you inject air while drilling to create a back pressure can help too. Now this would require a block plate with an air injection port. Beside on four cycle small engines you could simply remove the cylinder head; unless, got a cylinder jug like Honda. Then you just treat it as a two cycle jug.

Basically there is more than one way to do things.

Matter of fact tapping aluminum is a lot easier with the alcohol then with cutting oil like Tap Magic. As usual you tap a few threads, back out, clean the tap or drill bit. Reapply the lube and repeat as often as needed.

As Rivets said 99% of the time you are successful. That one 1% is a small risk to take besides the other option would be replace the head or cylinder jug otherwise. At least you tried.

sgkent said:

Huh? I was machinist in a well known high end racing and fleet machine shop once. I can't imagine any reputable mechanic letting drill and tap filings fall down into the cylinder to get caught in the cylinder and whiz around, or wedge the valves open a bit. THAT sounds like something from the third world or Bob's DIY Old Oak Tree Garage. I am out of this forum if that is the preferred method of repair. Frankly, I'd just get a good used head off Ebay from a seller with a 100% rating and 5,000 items, check it for warp and replace the head. Most heads are fairly easy to remove because small engines usually say in the manual to decarbonize them every so often.

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How many people actually remove a cylinder head every once in a while to decarbonize it? Way less that even remove the engine shroud to check for dirt, debris on cooling fines and top off engine.

How expensive do you think it would be to buy a used cylinder head off of EBay, remove the one on engine, then install the used one? Might as well adjust the valves while you are at it and lap them.

Read the other posts on handling the metal shavings. Happy Thanksgiving .

I thought that what decarbonizing fluid is for. On Stihl 4-mix brush cutters the carbon actually can seize the piston. The fluid cleans the cylinder, valves, rings, and the piston.

Interesting thread (pun intended) on spark plug holes.

Rivets said:

Sgkent, how do you repair a stripped spark plug hole on a 2-cycle engine? Buy a short block? I’ve saved a lot of engines by installing a helicoil with no disassembly. To keep chips outside the cylinder I coat my tap with tons of grease and slowly run the tap into the hole. Don’t go too far in before backing out the tap, cleaning it, regreasing, and repeat. It may take a half dozen passes, but I don’t remember a time, but cheaper than a tear down. I always inform the customer of the odds of possible failure before attempting, but almost everyone is willing to take the chance. Only once I can remember where I failed.

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We tigged it and machined a new plug hole. Sometimes on racing heads we also moved the ports and added a second plug. The only issue with a 2 cycle that was a challenge was keeping the cylinder perfectly round when honing or boring. They flex more. Anything else you need to know?

So essentially you disassemble and rebuild. You can’t convince me that given the cost of doing that many customers want it done. On top of that you are talking two very different engines, trying to compare apples and lemons. Don’t work that way in the small engine industry.

That's the attitude we face in the small engine and equipment repair business. Instead saving things that are savable they rather spend the money on ***, drugs, and booze. Now IF they are making tons of money with it then they are more willing to do things.

I was doing a project at just this week for parts only and the customer didn't want to spend a few dollars to add a decomp valve to his chainsaw to help him with his weaken arm. Yet he will spend thousands of dollars on an ATV to just tear up in the mountain terrain climbing over boulders and logs. Or adding options to just show off.

StarTech said:

customer didn't Yet he will spend thousands of dollars on an ATV to just tear up in the mountain terrain climbing over boulders and logs. Or adding options to just show off.

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Just don't diss me for pimping out my golf cart

I like the customer with the new $90K pickup complaing he needs a new $40 chainsaw bar.

was that you at the race track the other day?

Or was this this one yours?

StarTech said:

was that you at the race track the other day?
View attachment 72329
Or was this this one yours?
View attachment 72330

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I wish.

l008com said:

Last Fall, I was winterising my equipment and I accidentally stripped the spark plug hole on my yard vacuum. Its a 31 year old machine and I didn't turn that hard, so its probably a failure that has been inching its way to happening for a while.

But no worries, this is a great opportunity for me to make a video about repairing stripped spark plug holes with helicoil type repairs. I used one of those to fix the brake rotor mount on my mountain bike and it worked great.

So the question is, does anyone have any specific suggestions for a specific kit (with links) that is good and that has everything you need in one kit. Including the drill bit UNLESS its a standard size bit. But I don't think it it, its probably bigger than 1/2" right? So the bit, the coil, the install tool, the thread tap etc.

I know I could also repair this by just replacing the head. But I'm making a video out of it so I really want to use a repair kit rather than a replacement head.

Click to expand...

Helicoil is the way to go, quick and easy, make sure to use loctite on the helicoil so it doesn't back out. I use to strip the threads on an old vw all the time then I found copper anti-seize.

StarTech said:

Well those are hard to get started and causes a loose fitting. They are supposed to self feed but don't. I recently tried one on the Poulan with a strip plug hole. Almost never got it started and then kept wobbling around.

It is best to use a regular Heli Coil but those kits are expensive. And mainly only shops can justify the costs.

Click to expand...

The Runnings link looks like exactly what he needs. I see two problems: Running's only has stores in 12 states. They say it only includes the tap and four inserts, no tool to install nor drill bit. I think more research is needed. From another post maybe it uses a standard ½" drill bit. More importantly, specialized install tool was needed on Helicoils I've installed in the past.

I'm in the auto repair business not small engines. I can tell you 100% if you want a long lasting repair DO NOT USE A Heli-coil! if you have had this machine for 30 years your in it for the long haul and from the sounds of it you do preventive maintenance like changing a spark plug regularly. you may get 1 or 2 chances at it before the heli-coil pulls out of head. Time sert is the only way to go! unless you want to buy a cylinder,head and be done with it altogether. When you put the insert in the head red lock tite on the outside of the cert and you will be good for another 30 years!

Watch Taryl's video from the 19 min point.

For what it is....18mm to 14mm plug adapter. Way cheaper.

I used a helicoil thread repair kit I bought from aliexpress (for about $6), on a 9HP Craftsman snowblower. During the process of installing it I thought it would never work because it was very difficult to use the rethreading tool. I pounded it with a mini sledgehammer many times because it was so difficult to cut the new threads, and I thought that the new threads were stripped as I tried to cut them, but, when I finished, I inserted the spark plug with the helicoil and didn't tighten it too much. I started the engine and it ran fine. I wanted to use Loctite but thought the heat of the engine would be too much, so I didn't use any. I still need to test the engine again and run it for a long time to have more confidence in it.

... or maybe the guy who doesn't have the time and money to fix it right, but he is fully capable of spending the time and money to fix it two or three times... .

Not about spark plugs, but if hole strips, check the hole for depth and see if there are enough threads further down the hole. Then use a longer screw or bolt but use one long enough to reach the bottom. Carefully shorten the bolt until it will torque without hitting the bottom. You need to use all the thread available. I have used this in carburetor screws and starter mounting bolts. Never had problems.

Here is something we all should be aware of. A machinist friend tells me for a threaded hole to be at full strength the threads need to be 1.5 x the diameter of the screws. Well this makes these 9.5mm length 10mm plugs holes [2/3 strength] easily stripped and the 14mm short thread [45% strength] even easier to strip if over torqued. Now the 14mm long thread are at nearly 100%.

golfergordy said:

I used a helicoil thread repair kit I bought from aliexpress (for about $6), on a 9HP Craftsman snowblower. During the process of installing it I thought it would never work because it was very difficult to use the rethreading tool. I pounded it with a mini sledgehammer many times because it was so difficult to cut the new threads, and I thought that the new threads were stripped as I tried to cut them, but, when I finished, I inserted the spark plug with the helicoil and didn't tighten it too much. I started the engine and it ran fine. I wanted to use Loctite but thought the heat of the engine would be too much, so I didn't use any. I still need to test the engine again and run it for a long time to have more confidence in it.

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This is probably what you got.

Which is not a Helicoil set but is an insert kit. Very similar to Timeserts

Now this is a Helicoil set that I was looking for. Too bad the company don't a have complete kit like it for the 14mm so I get the next level and getting the 9/16 bit separately. But at least they have the full kits for the 10mm & 12mm plus the extra Helicoil to refill the kits.

sgkent said:

... or maybe the guy who doesn't have the time and money to fix it right, but he is fully capable of spending the time and money to fix it two or three times... .

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problem is when you pull a heli-coil out it usually takes the repair threads that hold the coil in play out with it. been there done that seen that. that is why the time certs are so much better. they are used to repair bores in engine blocks that hold heal bolts in that are torqued down really tight and they stan the test of time they are a permanent repair. they kits are really not all that expensive for the DIY person. and the repair process is essentially the same in you just drilling a bigger hole and metal bullet instead of threading in kite string

It is not the inserts I have the problem with its the tool the cheap kits that tries to ream to hole and thread it at the same time.

Now regular Time-serts even use a very similar threading tool. I waiting on a 9/16 3/8 Reduced shank drill bit so I cut out the old threads so can I try the above tool as a regular tap. Another difference is that Time-serts comes two styles. Gasket and taper seat designs where the kit I brought tries to do both with the same insert just swaggering the insert [Helical Inserts]. Plus Time-serts are also countersunked [no swaggering needed].

So basically we are discussing three different systems. True Helical coils, Helical coil inserts, and Time-serts.

yes for sure and in terms of longevity you have them from the least desirable to most desirable and the price has dropped when Time-serts first came out the price was astronomical and with ali-express and temu even time sert knocks offs are still better than a heli-coil. if it's just a cylinder head and it was mine I would just replace the head and be down with it if cheap enough to replace.

here's the threading tool I used. It worked, but wasn't easy. There were 4 inserts, one of which I ruined, and the other is in my snowblower head.