What is the function of the spring inside a spark plug

[grsthegreat]

I just found out that there is a small spring inside a sparkplug…….never knew that. Any idea whats it for. Tried a quick google search to no avail.

 

[chim]

Resistor?

 

[CliffordK]

Resistor?

Yep, that is what I was thinking. Google seems to indicate "Most resistor spark plugs use a monolithic resistor, generally made of graphite and glass materials," However, I'd imagine some also have simple springs.

Perhaps the spring is also to make contact between different halves of the spark plug.

 

[CliffordK]

Ok, this is the NGK site:

https://www.ngk.com/what-is-a-resistor-spark-plug

So, the resistor appears to be much deeper inside of the plugs.

That may indicate the spring is providing compression to keep everything in contact. I imagine the plugs, or the resistor, go through heat/cool cycles.

 

[bcp]

Does the spring allow the terminal to be pushed down into the plug a bit? Might be to insure contact if the boot slips up.

Bruce

 

[Wagtail]

Resistor?

I'd agree that this 'spring' is acting as a "coil resistor".

 

[wsc9tt]

Here is a diagram that shows a spring in a spark plug:

FAQ – Spark Plugs 101

Here is a sampling of the top questions we are most commonly asked about spark plugs, spark plug gap, heat range, resistor plugs and much more. Q: What is the function of a spark plug? The spark pl…

prostreetonline.wordpress.com

Most plugs don't have a spring like that, but notice that the spring is not the resister. That page doesn't say why it is there, but my assumption(*) is that it helps maintain electrical contact over a higher temperature range when the material of the resister expands at a different rate than the electrodes.

*) Wild ass guess from a EE who works in a totally different field

 

[bdhsfz6]

The spring is a resistor which reduces electromagnetic interference and extends the life of the sparkplug.

 

[DarkBlack]

Here is a diagram that shows a spring in a spark plug:

FAQ – Spark Plugs 101

Here is a sampling of the top questions we are most commonly asked about spark plugs, spark plug gap, heat range, resistor plugs and much more. Q: What is the function of a spark plug? The spark pl…

prostreetonline.wordpress.com

Most plugs don't have a spring like that, but notice that the spring is not the resister. That page doesn't say why it is there, but my assumption(*) is that it helps maintain electrical contact over a higher temperature range when the material of the resister expands at a different rate than the electrodes.

*) Wild ass guess from a EE who works in a totally different field

That’s a good drawing.
I’d agree mostly, except I’d guess myself, it’s about the thermal expansion of the electrode being greater than the ceramic, so the spring allows the long electrode to thermally expand towards the resistor when hot.
Notice the intentional hollow air space between the electrode and ceramic, except for one small area I’ve circled where it’s touching the ceramic for centering

 

[Thegrovefarm]

If the electrode can move, what keeps combustion gasses from moving up the center of the ceramic?
Spring stronger than compressed gasses?
Knots