Spark Plug question......

[Cruzinchris]

The spark plugs on my Lycoming 320 are all threaded into Heli-coils. On the last annual one of them got buggered when removing the plug and had to be replaced. What a pain. Yes, I used anti seize.

Would the plugs come out easier if the engine is warm/hot? The aluminum head would expand which helps, but the plug would too. I guess it comes down to which one has the largest coefficient of thermal expansion? Perhaps brush alcohol on the plug to cool it?

Thanks to the group.

 

[nrpetersen]

Aluminum will expand with temperature about twice as much as steel.

I clean the spark plug helicoil threads in the head with a small rotary wire brush in an electric drill.

What are you using for anti seize?

 

[Tom-D]

You should run a thread chaser in the heli-coils every once in a while.
that should end that problem.

 

[Lindberg]

The aluminum head would expand which helps, but the plug would too.

Even if they both expand at the same rate, the head will expand more (the hole is bigger than the plug) and the space in between them increases.

 

[hotprops]

gold color anti seize

 

[Tom-D]

gold color anti seize

Best is the NAPA nickel (silver color)

 

[nrpetersen]

Even if they both expand at the same rate, the head will expand more (the hole is bigger than the plug) and the space in between them increases.

It doesn't work that way. Steel expands about 6 microstrain per deg F, and aluminum about 12 microstrain/ degF The Helicoils (and the hole) are an infinitely small part of everything.

FWIW - I used silver colored /nickel-based anti seize but I had to be careful not to let it flow into the combustion chamber or it would short out the plug.

 

[Snowmass]

I have used hi-temp RTV for over 40 years. It seals as well as acts as anti-seize so no corrosion ever reaches the pristine threads.

 

[hotprops]

tom I agree with silver for aircraft cylinders except for Healy coil apps.i keep a small tube of gold just for coil apps .has worked well for 51 years

 

[Cruzinchris]

It doesn't work that way. Steel expands about 6 microstrain per deg F, and aluminum about 12 microstrain/ degF The Helicoils (and the hole) are an infinitely small part of everything.

FWIW - I used silver colored /nickel-based anti seize but I had to be careful not to let it flow into the combustion chamber or it would short out the plug.

Okay, the original question. Pull the plugs when the engine is hot or not?

 

[Snowmass]

If you use the correct anti-seize it should never matter. And I have found Hi-Temp RTV to be the best. Just try it and don't argue. You will be happy. But, hot should be better as you were already explained. I have never heard of any one pulling plugs per temperature.