A friend of mine who has a lot more money than me is interested in buying an Ultimate Driving Machine. Since he knows little about cars (other than he knows what he likes), he asked me to do some research for him on a BMW website. While there, I came across a forum discussion on the choice and installation of spark plugs. One member insisted that anti-seize should never be applied to spark plug threads and as evidence quoted the following information taken from Autolite and AC/Delco:
Autolite
We do not recommend the use of any anti seize products for installing spark plugs. Anti-seize compounds are typically composed of metallic, electrically conductive ingredients. If anti seize compounds come in contact with the core nose of the plugs, it can lead to a misfire condition. Anti seize 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.
AC/Delco
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.
Champion
The following material is excerpted from the Champion Spark Plug Handbook. It can be accessed at:
Champion spark plug shells (the threaded part) use an extruded steel to maintain exact tolerances. The extruded shell goes through a cold rolling process to form the threads. This prevents sharp edges which could cut new threads into aluminum cylinder heads. Once the shell is formed and threaded, it is zinc-plated to extend its life and reduce the chances of seizure in aluminum cylinder heads. Our latest technology combines Tin Tac" and ULTRASEAL'M coatings over the plating to further reduce corrosion and seizure. Champion recommends that you do not use an anti-seize compound, since one has already been applied to the plugs at the factory.
Intrigued, I went a-googling for any information I could find from NGK on this topic. I found this excellent Canadian website that lists the complete set of NGK Technical Bulletins. Go to:
Or, you can go directly here for NGK's take on the use of anti-seize compound, NGK Technical Bulletin #NGKSP-0907-1:
According to the Bulletin, NGK states that all their plugs are manufactured with a special metal shell (trivalent) plating to prevent damage to the cylinder head. For plugs with this special metal plating, anti-seize is not recommended during installation. Applying anti-seize to these plugs will cause the installer to mistakenly over-torque the plug in the cylinder head stretching the metal between the last thread and the seal between the cylinder head and plug. This increases the probability that the spark plug will either break during installation or upon removal.
For plugs without a special metal shell plating, NGK advises the use of anti-seize and provides photos of unplated plugs installed without anti-seize where the steel threads have bonded with the aluminum in the cylinder head requiring replacement or repair of the head.
Denso also warns against the use of anti-seize in their Spark Plug Installation instructions:
Specifically, they state: "If a thread lubricant such as grease is coated on the thread, tightening to the recommended torque is tightening too much; this has been linked to seal leakage. Do not use a thread lubricant."
Recommendations
One could simply stop using anti-seize and torque to the factory recommended specs when using shiny metal shell plated plugs as per the manufacturers recommendations, and be done with it.
Thinking it was the right thing to do, I've always used anti-seize, always used a torque wrench, and tightened the plugs to the middle of the range of the FSM recommended specs (11-16 ft/lbs; 15-22 Nm) for my car. Maybe this is a holdover from the days when plug threads were typically unplated (black) and driven into aluminum heads where damage would have occurred without a lubricant?
In the future, if I continue to use anti-seize I'll make sure its the lightest possible coating and torque the plugs to the lower end of the range (11 ft/lbs; 15 Nm) to guard against the possibility of over-tightening. One problem with the use of my torque wrench (5-85 ft/lbs; 3/8" drive) is that at the lower end of its range it tends to be outside its area of greatest accuracy and thus makes it difficult to know exactly how close I am to spec. In the interest of greater accuracy it might be better to use an inch/lb torque wrench (1/4" drive?) or to buy a Snap-on; the latter choice would be about as likely for me to afford as it would be for me to afford a new BMW.
What should you do? As always, I report, you decide.
Happy Motoring!
Autolite
We do not recommend the use of any anti seize products for installing spark plugs. Anti-seize compounds are typically composed of metallic, electrically conductive ingredients. If anti seize compounds come in contact with the core nose of the plugs, it can lead to a misfire condition. Anti seize 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.
AC/Delco
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.
Champion
The following material is excerpted from the Champion Spark Plug Handbook. It can be accessed at:
Champion spark plug shells (the threaded part) use an extruded steel to maintain exact tolerances. The extruded shell goes through a cold rolling process to form the threads. This prevents sharp edges which could cut new threads into aluminum cylinder heads. Once the shell is formed and threaded, it is zinc-plated to extend its life and reduce the chances of seizure in aluminum cylinder heads. Our latest technology combines Tin Tac" and ULTRASEAL'M coatings over the plating to further reduce corrosion and seizure. Champion recommends that you do not use an anti-seize compound, since one has already been applied to the plugs at the factory.
Intrigued, I went a-googling for any information I could find from NGK on this topic. I found this excellent Canadian website that lists the complete set of NGK Technical Bulletins. Go to:
Or, you can go directly here for NGK's take on the use of anti-seize compound, NGK Technical Bulletin #NGKSP-0907-1:
According to the Bulletin, NGK states that all their plugs are manufactured with a special metal shell (trivalent) plating to prevent damage to the cylinder head. For plugs with this special metal plating, anti-seize is not recommended during installation. Applying anti-seize to these plugs will cause the installer to mistakenly over-torque the plug in the cylinder head stretching the metal between the last thread and the seal between the cylinder head and plug. This increases the probability that the spark plug will either break during installation or upon removal.
For plugs without a special metal shell plating, NGK advises the use of anti-seize and provides photos of unplated plugs installed without anti-seize where the steel threads have bonded with the aluminum in the cylinder head requiring replacement or repair of the head.
Denso also warns against the use of anti-seize in their Spark Plug Installation instructions:
Specifically, they state: "If a thread lubricant such as grease is coated on the thread, tightening to the recommended torque is tightening too much; this has been linked to seal leakage. Do not use a thread lubricant."
Recommendations
One could simply stop using anti-seize and torque to the factory recommended specs when using shiny metal shell plated plugs as per the manufacturers recommendations, and be done with it.
Thinking it was the right thing to do, I've always used anti-seize, always used a torque wrench, and tightened the plugs to the middle of the range of the FSM recommended specs (11-16 ft/lbs; 15-22 Nm) for my car. Maybe this is a holdover from the days when plug threads were typically unplated (black) and driven into aluminum heads where damage would have occurred without a lubricant?
In the future, if I continue to use anti-seize I'll make sure its the lightest possible coating and torque the plugs to the lower end of the range (11 ft/lbs; 15 Nm) to guard against the possibility of over-tightening. One problem with the use of my torque wrench (5-85 ft/lbs; 3/8" drive) is that at the lower end of its range it tends to be outside its area of greatest accuracy and thus makes it difficult to know exactly how close I am to spec. In the interest of greater accuracy it might be better to use an inch/lb torque wrench (1/4" drive?) or to buy a Snap-on; the latter choice would be about as likely for me to afford as it would be for me to afford a new BMW.
What should you do? As always, I report, you decide.
Happy Motoring!
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