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This is question came up while trying to diagnose ignition coils unseating. I used anti-seize lubricant on the currently-installed spark plugs.

I'm planning to install a new set of three NGK DCPR8E spark plugs in a Rotax 1503 HO in a BRP RXT-X aS 260. There is disagreement between the official advice from BRP and NGK on the matter of lubrication. (I haven't found any advice direct from Rotax but BRP owns Rotax and the BRP manual seems pretty complete for engine maintenance.)

As you can see from the exerpts below, BRP recommend using anti-seize lubricant while NGK recommend against any lubricant.

On the one hand, I'm inclined to omit the anti-seize lubricant to see if the ignition coils stay seated. On the other hand, this is in a salt-water marine environment so I'm concerned that the spark plugs might seize to the head without the anti-seize lubricant. I'm hoping someone has some other reason or strategy to do one thing or the other.

Also, suppose I opt to follow the NGK recommendation an use no lubricant. How do I clear the remaining lubricant from the threads in the head?

BRP

The BRP manual includes the following text in the spark plug installation procedure:

Installing the Spark Plug

...

  1. Apply LOCTITE 767 (ANTISEIZE LUBRICANT) (P/N 293 800 070) over the spark plug threads to prevent possible seizure.

...

NGK

Page 8 of the NGK catalog includes, among other things, this text:

SPARK PLUG INSTALLATION TIPS

...

• NGK does not recommend the application of lubricant to spark plug threads as the resultant reduction of frictional forces at the thread faces will render the torque charts inaccurate and over tightening could occur

...

For what it's worth, the back of the spark plug box itself has this advice:

Spark plug box

I can guess at what those symbols mean, but it would just be a guess.

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  • The problem with anti-seize compounds is getting rid of them the next time you remove the plugs. Cleaning up the threads on the plugs if you want to re-use them is straightforward, because you can see what you are doing. Cleaning up the threads in the cylinder, without debris falling into the cylinder, is a different ballgame. If both sets of threads are clean and undamaged, they will seal properly at the correct torque without any sealing compound, and if not, you need to repair the threads (for example with helicoils), not try to fix the problem with Band-Aid.
    – alephzero
    Commented Sep 8, 2017 at 2:33
  • The warning triangle is (fairly obviously) "not for use in engines powering any type of aircraft" - which is irrelevant for the OP. Aircraft engines have (and need) a completely different standard for reliability - and certified maintenance engineers to make sure they are achieved, even for "simple" operations like changing plugs! In any case, these particular plugs may not be suitable for an engine with two independent, magneto-powered, plugs per cylinder, like many aircraft piston engines, rather than one plug and (most likely) an electronic ignition system
    – alephzero
    Commented Sep 8, 2017 at 2:47
  • The main picture seems to imply "insert the plug finger-tight plus 1/16 of a turn, then tighten a further 1/2 turn in a single continuous operation". No torque wrench required!
    – alephzero
    Commented Sep 8, 2017 at 2:52
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    I thought the 1/16 and 1/2 turn corresponded with the taper and gasketed flat seat types, respectively. (Note the arrows point to the seats.) I figured you can achieve 1/2 turn past finger-tight on the latter but not the former because the gasket crushes on first tightening.
    – alx9r
    Commented Sep 8, 2017 at 3:00
  • I'd suggest you pose this on a pwc forum, lots of folks with direct salt water experience.. (I never use antiseize but I run in fresh water..)
    – agentp
    Commented Sep 8, 2017 at 15:27

3 Answers 3

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It's ok to use the lube if you know what you are doing. Both NGK and BRP are correct, but it's important to understand where the disagreement in these recommendations comes from.

First of all, let's see what is good about using lube:

  1. Easier to remove the spark plug
  2. Less chance of thread damage, because it's easier to insert the plug

Then, why wouldn't we always use it? Why NGK says that over-tightening could occur? This is exactly because it's easier to insert the plug. Your torque wrench will click later if you are using lube, i.e. you'll be able to make more turns. This will put additional pressure onto both the plug seat and the head. That's what NGK means by saying that torque charts get inaccurate when using lube. Therefore, if you decide to use the lube on spark plugs, never tighten them to the spec. Reduce that number by 20-30%.

Now, the question is: is there a guaranteed good way of installing plugs with lube? Apparently there is one, and it involves measuring not the torque, but the angle at which you turn the plug when you insert it. Basically, when you make a 1/2 turn (or a 1/4 turn, or a full turn), you always put the plug deeper into the head this many millimeters, regardless whether you use the lube or not. Some plug manufacturers put the angle next to the torque: that's exactly the number you need to use this method. You'll need to tighten the plug by hand with the least force applied, and once the seat got snug with the head, and you can't finger-tight it any more, get a good wrench, and turn it some more (the spec says 90 degrees? that's 1/4 turn. 180? that's a half turn. 15 degrees? I hope you got good eye for that - or use an angle-torque wrench).

Here is the document from Bosch that has instructions for tightening plugs using torque wrench (both dry and lubed) and the angle method - but please remember that numbers may be different for other brands:

http://www.bosch-automotive-tradition.com/media/en/bosch_classic/teile_1/zuendkerzen/zuendkerzen_einbauhinweise.pdf

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I always use anti-seize whenever I'm installing spark plugs of whatever type for several reasons:

  1. If installing spark plugs into aluminum heads, it helps prevent pulling the threads out with the spark plug during removal.
  2. It seals the threads to help keep the combustion gasses inside the cylinder.
  3. It helps conduct heat.
  4. It better grounds the spark plug to the head.

I'm sure there's other things I could write down as well, but this is sufficient. Anti-seize does a lot more than act as a lubricant. As long as you don't over tighten a spark plug, you should have no fear of using it.

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  • When torquing down spark plugs, you should probably reduce torque about 20% when using anti-seize. If you a lubricated sparkplug to the unlubricated torque value, you might overtighten it.
    – Ives
    Commented Sep 8, 2017 at 9:00
  • If your using lube to help prevent pulling out threads then I'd be worried that your overtightening your plugs.
    – DamoC
    Commented Sep 8, 2017 at 9:01
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    @DamoC - I've never worried about it. What I worry about is the bi-metal (steel plug - aluminum threads) where the threads in the heads attach themselves to the spark plug and then get pulled out when removing spark plugs. I cannot say for sure this is what happened when I've had to put a thread repair kit in the head, but anti-seize will definitely help prevent it. I've had to do the repair more than once, but never where I've used anti-seize on the threads. Replacing threads in a head on a transverse V6 engine with it in the car IS NO FUN AT ALL. And that was replacing factory plugs.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Sep 8, 2017 at 10:13
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No need. If it's a new plug finger tighten it then give it half a turn more with a wrench, back it out then tighten quarter turn after finger tight.
If your re-using a plug then just finger tighten and then quarter turn.

You can clean the excess lube on the threads in the head with some carb cleaner or solvent on a lint free cloth, wrap it around a screwdriver and run it around the threads a few times until no more lube comes off.

If your worried about the salt water affecting the threads (would be fine assuming it's correctly tightened) put some petroleom jelly around the plug on the outside to create an external barrier like you would place it over clean electical connections.
Hope this helps you.

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