Spark plug extender???

[Raymond]

Okay boys and girls, what the heck is this?  See photos.  I pulled these out of a cylinder head I was given.  It was removed from an early 280SL decades ago.  The plug with the "extender" on it was in the #3 cylinder.  Was this one of those 1970's gimmicks that was supposed to save fuel?

[wjsvb ✝︎]

They were used to reduce plug fouling in engines that burned oil. Common in old "Stovebolt" Chevies and such.

[Jonny B]

Most interesting, always learning stuff.

Here are some background articles

https://www.easterneye.biz/things-to-know-about-spark-plug-non-foulers/

https://www.motorverso.com/spark-plug-non-fouler/

[Raymond]

Still seems a bit like snake oil to me.  But, you can surmise that the owner tried this, and whatever problem he had caught up with the engine.  Explains why the dealer replaced the engine.  Now, why did he keep the head?

[Shvegel]

The concept was if the rings were bad oil eas swirling up into the combustion chamber past the rings.  By shielding the spark plug you avoided getting coked up oil residue on your spark plugs.  They worked to a degree.  I think one of the best visual ways to determine ring sealing is to look at the piston tops.  If the edges of the piston tops are nice and clean it is likely that oil is washing up around the piston and misting the edges of the piston crown.

[Desertpagoda]

Thats an old school anti-fouling tip. It works by pulling the electrode up away from the combustion chamber. It absolutely works. We also used to use Aldor spark plugs in sick engines, they will fire even if soaked in oil.