What's new
Van's Air Force

The definitive Van's Aircraft support community! Buying, building or flying an RV? Join our exclusive family of mentors and enthusiasts!

Use of Thermal Paste on Auto Spark Plug Thread Associated with P Mag Install

B

bardample

Active Member
An aircraft maintenance engineer (;LAME in Australia) suggested I I use thermal conducting paste on the threads of the auto spark plugs that I will install with my PMags. I know there is no recommendation from EMag, but I understand this paste is used in Rotax installations. I plan on using antiseize on the outer adapter threads anyway. Any helpful advice? Jeff R Australia
 
bardample said:
An aircraft maintenance engineer (;LAME in Australia) suggested I I use thermal conducting paste on the threads of the auto spark plugs that I will install with my PMags. I know there is no recommendation from EMag, but I understand this paste is used in Rotax installations. I plan on using antiseize on the outer adapter threads anyway. Any helpful advice? Jeff R Australia
Click to expand...
Are you using the 14mm-18mm adapters? If so, a little antiseize on the 18mm adapter threads isn't a bad idea. If you have 14mm spark plug holes, it shouldn't be required. See #1 @ https://ngksparkplugs.com/en/resources/5-things-you-should-know-about-spark-plugs.
 
There is no reason to ever use any kind of paste or antiseize on any spark plug installed in a Lycoming. The helicoils are stainless therefore no galling is possible. Use of these products causes problems down the road as any paste eventualy dries and gums up the helicoil threads. Even the approved Champion stuff causes far more problems than it solves.
 
rocketbob said:
There is no reason to ever use any kind of paste or antiseize on any spark plug installed in a Lycoming. The helicoils are stainless therefore no galling is possible. Use of these products causes problems down the road as any paste eventualy dries and gums up the helicoil threads. Even the approved Champion stuff causes far more problems than it solves.
Click to expand...
+1

In addition there is NO value in improving thermal conduction here. Plenty of heat transfer via thread & flange face contact. Have no idea why Rotax recommends it our what flaws they have requiring it.
 
Here is Lycoming’s instruction on spark plugs:

Note the clear direction to use copper based antiseize.

But - for use with pMags and spark plugs adapters I experienced a problem with the adapters once I changed to copper based antiseize, the adapter threads eroded. I have been running these adapters for 20+ years and did not have this issue until after I changed to the copper based antiseize. The photo shows one of these adapters after ~200 hours or so. I replaced the adapters and went back to the old school graphite spark plug antiseize and the problem went away.

I recommend staying with graphite antiseize when using spark plugs adapters.

Carl
 

Attachments

  • 20220430_160415.jpeg
    20220430_160415.jpeg
    823.5 KB · Views: 36
I have the brass 18mm --> 14mm adapters, and I use nickel anti-seize on the 18mm side, and nothing on the 14mm side, since that's what NGK recommends. I started with the graphite and as @rocketbob said, it leaves a lot of gunk behind.
 
lr172 said:
Have no idea why Rotax recommends it our what flaws they have requiring it.
Click to expand...
My understanding its to improve thermal cooling performance in their water cooled aluminum head, avoiding a "hot spot" around plug which may reduce hardness over time. The paste aids heat transfer from plug to cylinder head acting as a water cooled heat sink. Remember as well that the Rotax plug fires more frequently than in a Lycoming, as typical RPM range is twice that of direct drive engines plus a wasted spark cycle on every other stroke. FWIW
 
"NGK spark plugs feature trivalent plating. This silver or chrome-colored finish on the threads is designed to provide corrosion resistance against moisture and chemicals. The coating also acts as a release agent during spark plug removal. NGK spark plugs are installed at the factory dry, without lubrication or anti-seize.

Anti-seize can act as a lubricant, altering torque values up to 20 percent, increasing the risk of spark plug thread breakage and/or metal shell stretch. Thread breakage can sometimes involve removing the cylinder head for repair. Metal shell stretch changes the heat rating of the spark plug and can result in serious engine damage caused by pre-ignition. Do not use anti-seize or lubricant on NGK spark plugs. It is completely unnecessary and can be detrimental."
 
I hope you take a mill file to flatten out that dent so that the copper gasket has a flat surface to seal on. And, since this one was installed/removed via Vise Grips or Channellocks (aye no!), it would be a good idea to inspect ALL of the adapters.

EDIT: Nevermind. I see that you replaced them already and hopefully used a 6-point socket.

1762907003299.jpeg
 
Last edited:
Thankyou all for your replies. I think I shall avoid any thermal paste( on spark plug ) and copper based anti seize ( on adapter) as Carl advises.
 
You must log in or register to reply here.
Back
Top