Spark Plug Threads

AlanM

Original poster
Member
May 19, 2013
3
Hi, I've had my 2007 Trailblazer for just about a year now. It has been great, hasn't really given me any problems. The idler pulley was making a little noise so I changed it yesterday, no big deal, noise went away. Decided to check a plug or two since I was under the hood. The truck has just over 106k and I don't know who may or may not have done any work to it before I bought it. Anyway, I pulled a coil pack off and stuck my plug socket down in there. I broke the plug loose but then it didn't feel like it was going to loosen up. Felt like it might be pulling the threads out of the head. Anyone had trouble with this before? I just tightened it back up (thankfully it did tighten up) and tried one other which felt the same way. The truck runs fine just like to keep a check on things. Thanks for any help!
 

gmcman

Member
Dec 12, 2011
4,656
Removing plugs from an aluminum head makes my palms sweaty....every time. When you remove the plugs do this with the motor cold and it will feel kinda gritty. Just be sure when you reinstall them you use some anti-seize and torque them to 180 inch-pounds, about 15 foot pounds. Torque the coil pack bolts to 89 inch pounds and also use anti-seize.

Please don't guess, use a torque wrench.:thumbsup:
 

AlanM

Original poster
Member
May 19, 2013
3
cool. thanks.

on a different note, you had to change an axle seal on yours? I've done it on my Camaro, guess it should be basically the same...
 

CaptainXL

Member
Dec 4, 2011
2,445
Kind of shocked with the advice going around here lately.

DO NOT use anti seize on aluminum heads or spark plugs. A big no no.

Always torque engine parts. Spark plugs are 13ft/lbs. Make sure threads are clean and dry before torquing.

Bolts and plugs will not torque accurately using lubricants. On an aluminum head this is very important.
 

gmcman

Member
Dec 12, 2011
4,656
AlanM said:
on a different note, you had to change an axle seal on yours? I've done it on my Camaro, guess it should be basically the same...

:confused: Please elaborate.
 

gmcman

Member
Dec 12, 2011
4,656
CaptainXL said:
Kind of shocked with the advice going around here lately.

DO NOT use anti seize on aluminum heads or spark plugs. A big no no.

Always torque engine parts. Spark plugs are 13ft/lbs. Make sure threads are clean and dry before torquing.

Bolts and plugs will not torque accurately using lubricants. On an aluminum head this is very important.


I'm going to be the bad guy....here's my take on it. Using anti seize can cause problems, I don't see how it's a no-no unless used incorrectly. Main problem is over-torquing the plugs, reduce the torque by about 15-20% and go with it, 15 ft/lbs is plenty and my limit. I use only a small film starting about 2-3 threads above the end to avoid any near the base of the plug.

Steel and aluminum don't mix too well, especially with a 100K interval. Here's some info I found, all basically revolves around users over-torqueing the plugs and I feel that's why warnings are given. If I'm wrong then feel free to bash.

From AC Delco:
Quote:
Do not use any type of anti-seize compound on spark plug threads. Doing this will decrease the amount of friction between the threads. The result of the lowered friction is that when the spark plug is torqued to the proper specification, the spark plug is turned too far into the cylinder head. This increases the likelihood of pulling or stripping the threads in the cylinder head. Over-tightening of a spark plug can cause stretching of the spark plug shell and could allow blowby to pass through the gasket seal between the shell and insulator. Over-tightening also results in extremely difficult removal.

From Autolite:
Quote:
We do not recommend the use of any anti seize products for installing spark plugs. Antiseize compounds are typically composed of metallic, electrically conductive ingredients. If antiseize compounds come in contact with the core nose of the plugs, it can lead to a misfire condition. Antiseize compounds can also have a torque multiplying effect when installing plugs. This can lead to thread distortion and thread galling resulting in cylinder head damage. Autolite spark plugs are nickel plated to resist the effects of corrosion and seizing. However, plug seizure is aggravated further when steel plugs are installed into aluminum cylinder heads for a long period of time. You may want to consider the periodic inspection of the plugs to reduce the likelihood of plug seizure during extended plug service intervals.

From NGK:
Quote

The use of anti-seize on spark plugs is only recommended on those brands that
do not offer a special metal shell plating. Spark plugs that have a shiny silver
appearance on the metal body usually indicate that the spark plug is
manufactured with special metal shell plating.
 

AlanM

Original poster
Member
May 19, 2013
3
thanks for the info!

as far as the rear axle seal that I mentioned...I was rotating tires today and noticed some gear oil around the wheel flange/brake rotor on the right rear. so, I guess I'm be changing the axle seal some time...
 

CaptainXL

Member
Dec 4, 2011
2,445
gmcman said:
15 ft/lbs is plenty and my limit.

Ok, well whatever floats your boat. The service manual says 13 ft/lbs dry. So if you are torqueing them to 15 ft/lbs wet then you might as well torque them to 20ft/lbs dry. It takes more torque to tighten a fastener wet.

The whole issue about using anti sieze is overstated. I can't imagine how someone would have a problem removing plugs torqued to 13 ft/lbs. It's silly. And if someone is using it then they would have to be ignoring the thermo resistive and electrical issues accompanying it's usage.
 

Sparky

Member
Dec 4, 2011
12,927
gmcman said:
I'm going to be the bad guy....here's my take on it. Using anti seize can cause problems, I don't see how it's a no-no unless used incorrectly. Main problem is over-torquing the plugs, reduce the torque by about 15-20% and go with it, 15 ft/lbs is plenty and my limit. I use only a small film starting about 2-3 threads above the end to avoid any near the base of the plug.

Steel and aluminum don't mix too well, especially with a 100K interval. Here's some info I found, all basically revolves around users over-torqueing the plugs and I feel that's why warnings are given. If I'm wrong then feel free to bash.

From AC Delco:
Quote:
Do not use any type of anti-seize compound on spark plug threads. Doing this will decrease the amount of friction between the threads. The result of the lowered friction is that when the spark plug is torqued to the proper specification, the spark plug is turned too far into the cylinder head. This increases the likelihood of pulling or stripping the threads in the cylinder head. Over-tightening of a spark plug can cause stretching of the spark plug shell and could allow blowby to pass through the gasket seal between the shell and insulator. Over-tightening also results in extremely difficult removal.

From Autolite:
Quote:
We do not recommend the use of any anti seize products for installing spark plugs. Antiseize compounds are typically composed of metallic, electrically conductive ingredients. If antiseize compounds come in contact with the core nose of the plugs, it can lead to a misfire condition. Antiseize compounds can also have a torque multiplying effect when installing plugs. This can lead to thread distortion and thread galling resulting in cylinder head damage. Autolite spark plugs are nickel plated to resist the effects of corrosion and seizing. However, plug seizure is aggravated further when steel plugs are installed into aluminum cylinder heads for a long period of time. You may want to consider the periodic inspection of the plugs to reduce the likelihood of plug seizure during extended plug service intervals.

From NGK:
Quote

The use of anti-seize on spark plugs is only recommended on those brands that
do not offer a special metal shell plating. Spark plugs that have a shiny silver
appearance on the metal body usually indicate that the spark plug is
manufactured with special metal shell plating.

So.... You acknowledge that using anti seize on plugs can cause problems, quote 3 plug manufacturers who say not to use it, then continue to recommend using it anyway? :confused:

I'm with CaptainXL and the plug makers on this one. And as he mentioned 15 ft lb is beyond spec dry, let alone wet...
 

CaptainXL

Member
Dec 4, 2011
2,445
There are some plug manufacturers that tell you to torque their plugs to 15-16 ft/lbs. But the service manual has precedence at 13 ft/lbs. Not a huge difference but it does provide a reference in case you have no clue what the torque is. You will probably be surprised. 13 ft/lbs is not that tight.
 

gmcman

Member
Dec 12, 2011
4,656
Sparky said:
So.... You acknowledge that using anti seize on plugs can cause problems, quote 3 plug manufacturers who say not to use it, then continue to recommend using it anyway? :confused:

I'm with CaptainXL and the plug makers on this one. And as he mentioned 15 ft lb is beyond spec dry, let alone wet...

Did you read the reason as to why I stated there was issues with anti seize. That was because of over torqueing the plugs.

Yep, you're correct on the 13 ft lbs though, I thought I had read it was 13-19 but I'm wrong. Considering 15 ft lbs + 20% = 18 ft lbs I figured it was in the range. I understand anti seize makes for a wet value but it's not penetrating oil.....still wet though.

I will back mine down to about 11 with the anti seize. I have never lost a set of threads with anti seize, but have had issues not using it so it's something you will need to make your own decision on.
 

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