The use of anti-seize on spark plugs is only recommended on those brands thatĭo not offer a special metal shell plating. You may want to consider the periodic inspection of the plugs to reduce the likelihood of plug seizure during extended plug service intervals. However, plug seizure is aggravated further when steel plugs are installed into aluminum cylinder heads for a long period of time. Autolite spark plugs are nickel plated to resist the effects of corrosion and seizing. This can lead to thread distortion and thread galling resulting in cylinder head damage. Antiseize compounds can also have a torque multiplying effect when installing plugs. If antiseize compounds come in contact with the core nose of the plugs, it can lead to a misfire condition. Antiseize compounds are typically composed of metallic, electrically conductive ingredients. We do not recommend the use of any anti seize products for installing spark plugs. Over-tightening also results in extremely difficult removal. 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. This increases the likelihood of pulling or stripping the threads in the cylinder head. 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. Doing this will decrease the amount of friction between the threads. IMO it makes more sense to ensure the bolt is in the lubricated condition (unless there is a good engineering reason as to why it must be installed dry) as that allows for better spark plug tension control in real-world environments.ĭo not use any type of anti-seize compound on spark plug threads. Once it is in this condition, no further amount of lubrication will make a difference. It takes VERY little residual oil from your fingers to move the threaded joint into the lubricated condition - often just picking up a bolt by the threads with fairly clean hands will transfer enough to make it happen. You would need to manually and chemically clean each set of mating threads to get a true dry thread condition. One other thing I come across frequently is many folks think that 'dry' torque values mean 'without any oil or anti-seize applied by you' which is WRONG! If you have a bolt tension gauge, you can easily see that the difference between true clean & dry threads and what you'll frequently come across in your engine bay is night & day. I could go through the derivation of this value if anyone else wants to open up their sophomore-level mechanical engineering textbooks, otherwise please just take it as a good rule of thumb. Reducing torque values by 20% is the common rule of thumb. They vary greatly depending on the plug type. You just have to be careful to pay attention and use the right ones. Most plug manufacturers give angle torque specs for their various plugs. The added friction created by the dirt in the threads is probably adds about as much friction as the lubricant reduces. Make sense?įor spark plugs, if you're using antiseize on a cylinder head in service, I think you're better off either tightening to the low end of the unlubricated spec (if there's a range), or just keeping it the same-unless you aggressively clean up the threads. Friction torque is just a proxy for that (and an inaccurate one). It doesn't matter how tight it is to turn the bolt, what matters is the tension between the plug and the cylinder head. That's why you reduce the torque for a lubricated fastener. If the bolt spins more easily (as a lubricated fastener will), then the joint will be under more tension for the same amount of friction applied to the fastener. You're right, the torque wrench doesn't know, but you're confusing bolt tensions with friction torque. Maybe I'm crazy, but this is what logic tells me. The torque wrench will 'click' at say 20 ft.lbs, with anti-sieze or not. I mean, the torque wrench dosn't know if the plug has anti-sieze on it. I've heard this before but don't beleive it.
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