# Spark plug thread



## Teafuz (Dec 27, 2020)

I have a Troy Bilt electric start, which wouldn't start. I had a mechanic friend take a look at it, removed the spark plug, but can't get it back in because the threads are damaged. I'm wondering if anyone knows what the general price range is for bringing it in to be repaired/rethreaded??


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## Toro-8-2-4 (Dec 28, 2013)

Go to the autoparts store and buy a spark plug rethread kit. They are very common and you should not have trouble finding one. Them have your mechanic friend to it for you. I have never paid anyone to do it. I have always done it myself. Should not take more than an hour for anyone with mechanical skills. You can ask around for what the common shop rate is in your area.


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## tabora (Mar 1, 2017)

Teafuz said:


> the threads are damaged.


If the threads are still mostly there, purchase an appropriate size backtap and fix it yourself...








Powerbuilt 14 Millimeter Back-Tap Thread Repair Tool - 640811 | eBay


SKU: 640811. A mandrel is then drawn back, expanding the tool's threaded area and threading into the clean threads at the bottom of the spark plug hole. Made in the USA. We know tools! Tool setsBrowse all.



www.ebay.com


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## orangputeh (Nov 24, 2016)

be sure to use grease on the tool to remove filings. you tube has some good videos on repairing cross threaded spark plug holes.


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## tpenfield (Feb 24, 2015)

Welcome, @Teafuz 

A shop will probably want to replace the cylinder head if the threads are stripped. Expect to pay a lot . . . $400+ would be my guess.

As recommended, you could try one of the re-thread kits . . . not sure if you'd have to remove the cylinder head to do that though . . . Maybe a shop would do that for $250 ish


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## RIT333 (Feb 6, 2014)

Wow tpenfield, if your price quotes are close to correct, you scare me into never wanting to ever change another spark plug again. Fortunately,i have never stripped a spark plug hole...yet. 

Really, $250 just to cut new threads ? I worked in the wrong field.


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## JLawrence08648 (Jan 15, 2017)

Do the back tap repair first, good chance of it working. Put some graphite Never-Seize on the threads.


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## Oneacer (Jan 3, 2011)

Of all my equipment I own, and throughout all my years, I think I might have changed one plug.

Why people think they have to change a plug every season is beyond me ?????

And many don't even know the repercussions of screwing into aluminum if not done properly.


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## classiccat (Mar 1, 2014)

I've had great luck with the safe-A-thread by helicoil.

Remove Head
Use tool to simultaneously carve out a new hole and cut threads for insert. *
Once the threads are cut in the head, clean out (I use brake cleaner)
Apply anti-seize on a spark plug and put the insert on the spark plug. NOTE: the disrupted-thread end (staking spikes) of the insert goes on the plug 1st (outside of the head).
Put high-temp red thread-locker on the insert
temporarily mount the head on the engine
Insert spark plug/insert into the head and torque it over the recommended spark plug torque (I usually go for 25 ft-lb)
*!!! Allow 24hrs for thread-locker to setup !!!*
After 24hrs, remove spark plug...insert should stay in place.
Remove head and put a small block of wood under the spark plug hole.
Use staking tool to drive the spikes into the head locking it in place.
* to ensure the thread cutting tool stays true, I use my drill press to keep pressure on it.


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## tpenfield (Feb 24, 2015)

RIT333 said:


> Wow tpenfield, if your price quotes are close to correct, you scare me into never wanting to ever change another spark plug again. Fortunately,i have never stripped a spark plug hole...yet.
> 
> Really, $250 just to cut new threads ? I worked in the wrong field.


Just my guess, figuring what a shop would charge to disassemble the engine coverings, remove the cylinder head, replace the head (or repair the threads) and then put it all back together. . . test run.

Maybe 4 hours of labor . . . perhaps a bit more, plus parts . . . What do shops charge for labor? $75/hour maybe?


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## orangputeh (Nov 24, 2016)

In most cases that I have worked on the back tapper tool or thread chaser tool ( sorry no links ) worked for me. The only time it didnt work and the head had to be removed is when an old lady insisted in screwing in plug ALL the way even though it was going in wrong.

FYI ( this is mechanics 101 ) you start a spark plug BY HAND to make sure it is going in correctly. Any resistance at all means STOP , back it out and try it again. Only use the socket and ratchet wrench when you have it in most of the way by hand.
Plus never OVER TIGHTEN. On a new plug just tighten 1/4 - 1/2 turn extra when you feel it tight. 

Shops wont use tools to repair threads because I was told they can not guarantee repair so they have to remove head , It is about a $250-400 repair in my town. That's why I have so much business. Been successful with back tappers and thread chaser tools ( so far , knock on wood ) except that old lady. I turned down her job and told her to take to dealer.

boy was she upset.


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## Toro-8-2-4 (Dec 28, 2013)

Is the point of the back tapper to pull the chips up and out so you do not have to remove the head? Basically Saves the time of removing the head?


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## Toro-8-2-4 (Dec 28, 2013)

oneacer said:


> Why people think they have to change a plug every season is beyond me ?????


I would say they think this because most owners manuals tell them to change it every so many hours of run time(I have seen anywhere from 50 to 100 hrs) or every year. I think it is that simple.


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## Oneacer (Jan 3, 2011)

Lol, ...... I think that the spark plug manufactures have a hand in that ....😊


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## orangputeh (Nov 24, 2016)

oneacer said:


> Lol, ...... I think that the spark plug manufactures have a hand in that ....😊


I have pulled dozens of 15-20-25 year old plugs out of Hondas that were still working fine.


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## 3vanman (Nov 21, 2017)

Teafuz said:


> I have a Troy Bilt electric start, which wouldn't start. I had a mechanic friend take a look at it, removed the spark plug, but can't get it back in because the threads are damaged. I'm wondering if anyone knows what the general price range is for bringing it in to be repaired/rethreaded??


Just wondering, what type of engine is on your Troy Bilt? Might be cheaper to replace the head, depending upon availability. 
No reason why you or your "mechanic friend" could not do that. 
Or option B, take the machine to a small engine shop. 
Yes, about 2 hours for most machines to re and re the head, but you might find one locally who (provided the thread damage is minimal) can run a thread chaser which could work out even "cheaper".


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## 3vanman (Nov 21, 2017)

You might find this video helpful


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## 140278 (Aug 27, 2020)

orangputeh said:


> I have pulled dozens of 15-20-25 year old plugs out of Hondas that were still working fine.


thats because honda uses real ngk's not torch like loncin and others


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## Bricklayer (Dec 29, 2020)

I just went through this myself.
I got a good deal on an Ariens Deluxe 28 SHO. Only used twice in the last two years. She told me she put a new spark plug in it this year.
I got to thinking when I got it home, I should check to see if she used a ngk plug.
It was in so crooked, I had to take muffler off to remove the plug.
She had started it crooked, and only ran it in a few turns, luckily.
I could not get new plug to start straight, it kept following the crooked threads.
Ordered the back tap from Amazon, around 5 passes, increasing the size each time, the plug went in with my fingers. Worked perfectly!
The snowblower was running with the crooked plug, only run in a few turns. I am very fortunate that I checked the plug before using it for any amount of time.


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## Toro-8-2-4 (Dec 28, 2013)

3vanman said:


> You might find this video helpful


That is a great tool to have as suggested by Donyboy. You can also use it on your car. Works on O2 sensor threads as well. The handful of times I have used it, I removed the tool serveral times to wipe away the chips and add more grease.


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## WrenchIt (Dec 6, 2020)

The instructions for a helicoil said to put anti seize on the plug threads. If you do this on a spark plug - or any fastener that you will tighten to a torque spec, reduce the torque 15 to 20%. Torque specs are for *dry* fasteners, not lubed with anti seize. If I did a helicoil, I'd research or call helicoil to find out if I should remove all a-seize from the helicoil after it is properly installed, and from the spark plug threads as well.


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## BNSFguy (Nov 2, 2019)

WrenchIt said:


> The instructions for a helicoil said to put anti seize on the plug threads. If you do this on a spark plug - or any fastener that you will tighten to a torque spec, reduce the torque 15 to 20%. Torque specs are for *dry* fasteners, not lubed with anti seize. If I did a helicoil, I'd research or call helicoil to find out if I should remove all a-seize from the helicoil after it is properly installed, and from the spark plug threads as well.



Yup. Most spark plug website will tell you not to use anti-seize because of just this: it's a lubricant and people end up over torqing the spark plug. Spark plug manufacturer's usually include a coating on the threads and therefore don't require, or advise using anti-seize. Here's NGK website





__





5 Things You Should Know About Spark Plugs - NGK Spark Plugs


The five things you should know about spark plugs include information on anti-seize, corona stain, gapping fine wire, torque and copper spark plugs.




ngksparkplugs.com


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## WIHD (Dec 15, 2019)

Some folks state "screw in plug by hand"....in small spaces with big hands this can be awkward.

Buy a 1 foot length of rubber radiator hose at any auto parts store ($0.39). Press plug end into hose, use foot long hose to screw the plug in. Allows one to easily reach a recessed space and also prevents cross threading as if the plug tries to go in crooked, it will just spin inside the rubber hose and not screw into the engine.

This is what I do on Harleys anyway. Also prevents a wrench from tapping on the bikes gas tank causing a dent or paint damage. YMMV


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## Johnny G1 (Jan 28, 2020)

Gotta look after them ole hogs, wouldn't want to put any more scratches on it, never usully have to put a wrench near them. LOL


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## 140278 (Aug 27, 2020)

depends on the hog no issues changing plugs for me


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## ST1100A (Feb 7, 2015)

I always tell people to NEVER EVER coat spark plug threads with anything.
Never coat them with oil, because the oil will burn and end up down at the tip causing carbon build-up that will coat or "Coke" at the tip of the plug threads and harden. Then when the plug is removed there is a very high chance of damaging the threads of the head when it is removed, and the removal will usually be a tight hard removal.
Never coat a spark plug thread with "Never Seize". Never seize is very fine metal dust, either aluminum or copper, combined with oil, and it will do more damage than oil alone, because the fine metal dust will melt due to combustion chamber heat at the plug tip, and drip into the combustion chamber, scoring cylinder walls, damaging rings, valve seats and faces, plus where it "Melts", it will solidify in the threads and cause a lot of damage to them when the spark plug is removed, taking the threads with it upon removal.
Not only that, as it burns and drips into the combustion chamber, it will effect the spark plug and firing, fouling it and causing a carbon build-up on the plug tip and in the cylinder head.
We have repaired or replaced too many cylinder heads to count because people put oil or Never Seize on the spark plug threads, and when it came time to remove the spark plug, the threads of the head were removed with the plug, caused by the deposits left at the end of the threads.


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## farmer52 (Dec 27, 2020)

WIHD said:


> Some folks state "screw in plug by hand"....in small spaces with big hands this can be awkward.
> 
> Buy a 1 foot length of rubber radiator hose at any auto parts store ($0.39). Press plug end into hose, use foot long hose to screw the plug in. Allows one to easily reach a recessed space and also prevents cross threading as if the plug tries to go in crooked, it will just spin inside the rubber hose and not screw into the engine.


I use the spark plug socket and an extension/swivel in hard to reach spaces. Then use my hand/fingers to screw the plug into the engine until hand tight. Then attach the ratchet and tighten. Even when I remove the spark plug I usually just break it loose then use my hand/fingers to unscrew.


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