Copper grease on Spark Plugs?

[Forrest Gump]

To grease or not to grease?

When refitting my spark plugs today I questioned if it’s correct to put a smear of copper grease on the threads.
The heads on my C3 are alloy so it’s somewhat instinctive to put some kind of anti-seize on the threads to avoid ripping out a thread when removing a plug. I always use copper grease on header bolts and other ancillaries but spark plugs rely on good electrical conductivity to the heads. So what to do?

I decided to look up the plug manufacturers (Autolite) installation instructions.....They say NO anti-seize or grease is needed on their plug threads because they are nickel plated and therefore won’t seize.
They say grease can cause issues with heat transfer and electrical conductivity, plus lubrication of threads can lead to the plugs being over tightened

It’s still not totally conclusive though because they threw-in that if the vehicle manufacturer recommends anti-seize then it should be used!

 

[johng]

It can definitely be dangerous to lubricate bolts and then tighten to the specified torque, if lubrication of that bolt was not specified. There is a real risk of breaking the bolt or stripping the thread if you remove the friction in the joint.

 

[Vetman]

I use copper grease on my plugs in the alloy heads. No problems and they feel smoother when installed. Copper should be a good conductor. Slight baked grease deposit on the end of the threaded part.

 

[Roscobbc]

It can definitely be dangerous to lubricate bolts and then tighten to the specified torque, if lubrication of that bolt was not specified. There is a real risk of breaking the bolt or stripping the thread if you remove the friction in the joint.

Surely torque settings will apply to 'new' components or certainly older components with theads that have been 'chased' with an appropriate tap or die and chemically cleaned to remove any crud (which would otherwise adversely effect torque readings). I'm guessing only then will OEM torque settings be accurate.
Probably why manufacturers of high tech aftermarket items like cylinder heads publish 'stretch' measurements (rather than torque settings) using a specified grade of bolt (or stud & nut). An altogether more accurate method of using fasteners (but one than demands regular fastener replacement)

 

[johng]

Ross you are right in that torque values are chosen to achieve a particular clamp force in a joint under known conditions (new bolts, lubed or not, etc). For most joints the bolt is used in it's elastic range (ie the bolt is not taken into plastic deformation) and there is a degree of variation that can be tolerated. For critical joints like cylinder head bolts, the bolts are often "torqued to yield". This means they are intentionally taken into plastic deformation, quite often by specifying a torque plus an angle (eg tighten to 100Nm plus 90 degrees). In this case you really should use new bolts every time you replace them. When I worked at Ford, I had engineers whose job was solely instrumenting bolts to measure clamp force and determine tightening strategies for critical joints.

 

[Roscobbc]

Ross you are right in that torque values are chosen to achieve a particular clamp force in a joint under known conditions (new bolts, lubed or not, etc). For most joints the bolt is used in it's elastic range (ie the bolt is not taken into plastic deformation) and there is a degree of variation that can be tolerated. For critical joints like cylinder head bolts, the bolts are often "torqued to yield". This means they are intentionally taken into plastic deformation, quite often by specifying a torque plus an angle (eg tighten to 100Nm plus 90 degrees). In this case you really should use new bolts every time you replace them. When I worked at Ford, I had engineers whose job was solely instrumenting bolts to measure clamp force and determine tightening strategies for critical joints.

Fascinating that many people ramble-on about having used aviation grade fasteners on a specific car or engine build - you then look at an ARP data sheet and understand that even the basic grade blackened steel or stainless bolts and studs recommended for automotive use are generally way above aviation standards and there are still a couple more grades higher you can choose from (like for top fuel engines) - not like the 'old days' of BA, BSF, Whitworth and UNF threads (not forgeting gas and water theads)

 

[Forrest Gump]

I must admit I prefer to not use a torque wrench on spark plugs or the other bolts going into the alloy heads, like header and intake manifold bolts. I prefer to use feel and experience. Where aftermarket parts are attached with aftermarket bolts, thread insertion will vary. If you can identify what the torque should be (and it’s usually possible to find a few answers there too) it might not be right for your situation (John’s engineers needed). I bet plenty of threads have been stripped by putting blind faith in the torque wrench.
I goes out of the window on some fixings where you can’t get a socket on like the centre bolts on the intake manifold and the end header bolts.

 

[Mad4slalom]

I must admit I prefer to not use a torque wrench on spark plugs or the other bolts going into the alloy heads, like header and intake manifold bolts. I prefer to use feel and experience. Where aftermarket parts are attached with aftermarket bolts, thread insertion will vary. If you can identify what the torque should be (and it’s usually possible to find a few answers there too) it might not be right for your situation (John’s engineers needed). I bet plenty of threads have been stripped by putting blind faith in the torque wrench.
I goes out of the window on some fixings where you can’t get a socket on like the centre bolts on the intake manifold and the end header bolts.

Nothing feels worse to me than a dry thread , either tightening or loosening , if you are have to force it or it is squeaking or groaning then the risk of stripping or damage is greater. I clean threads with a wire brush. Apply some copper grease and then almost completely remove it with a rag. You will Feel the difference and much more chance of it going back in and coming out again intact , a few months down the line.

 

[Roscobbc]

Even with spark plugs - when removed there is always some residual lubricant on threads - interesting if you consider the typical cylinder head temperatures.

 

[Mad4slalom]

Even with spark plugs - when removed there is always some residual lubricant on threads - interesting if you consider the typical cylinder head temperatures.

Agreed, that is my thinking , I wipe it virtually all off, just leaving a small residual amount which is usually enough to stop them siezing therefore reducing the risk of thread damage to head or plug. . One thing for sure is more damage is caused by dry threads than by lubed ones.

 

[Roscobbc]

Agreed, that is my thinking , I wipe it virtually all off, just leaving a small residual amount which is usually enough to stop them siezing therefore reducing the risk of thread damage to head or plug. . One thing for sure is more damage is caused by dry threads than by lubed ones.

Especially with ally heads. 'fresh' heads with newly tapped threads will understandably have relatively 'tight' threads. As most of us know, access to spark plugs can be challenging with headers. Even more so I guess with a big block. Main issue I can have is actually getting the plug thread correctly aligned with the tapped head thread before tightening up.

 

[teamzr1]

Consider and adjust for the fact anything added to the threads will affect the correct torque value of the plug

 

[Roscobbc]

Thing is.......spark plugs are the very thing I don't use a torque wrench for.......

 

[Mad4slalom]

Thing is.......spark plugs are the very thing I don't use a torque wrench for.......

Me niether , its a “feel thing” wheel nuts and head bolts etc then its correct value with a torque wrench. I find a lot of times on grand piano legs people have either reamed them up rediculously tight or they are hanging off

 

[teamzr1]

Life was so much easier before the C5s
By then, GM began using torque to yield bolts, and you needed a NASA degree just to properly tighten bolts
Example :

Proper Installing Head Bolts