OT: Brass Spark Plug

[Cecil Walker]

Many years ago i bought a 1908 (est) Foos 2 HP Tank Cooled stationary engine with a brass spark plug. I sold the engine last month, but kept the spark plug because it was unique, over 4" in total length, 3/4" pipe thread, mica insulation, take apart, with an extendable electrode.

Why a brass spark plug???? corrosive enviroment? near saltwater?? Opinions?

Anyway, here's a pic.

[Just Bob Again]

You're sure it wasn't rebuilt during the last hundred years? Original plug may have been a smaller fine thread. Rebuilder needed to re-thread a stripped smaller fine-thread plug. 3/4 pipe was the closest he had. Brass is a whole lot easier to put a pipe thread on than steel. Nice job, too. That looks prettier than I'd expect from a factory piece.

[Carld]

Just from the looks of it I venture it's home made by some small machine shop as Just Bob Again said in some past repair. He probably didn't have a tap like the original plug thread soooo.

I'm curious what kind of plug you put in it???

[JCHannum]

I don't recall seeing brass sparkplugs, but that is no reason to say there are not any. Many early plugs did use pipe threads and most were of two piece construction. Mica was also a common material for insulators.

The early years of the IC engine saw many innovations and designs that did not stand the test of time, and just about anything was tried with varying success before some degree of standardization began to appear.

[macona]

I have a few spark plugs in 3/4" pipe thread as well. An old pink ceramic Firestone and the champion thats in my Sattley H&M.

There are so, so many different designs of spark plugs its crazy.

[Your Old Dog]

Could brass plugs have been used in the air craft industry?

http://ntrs.nasa.gov/archive/nasa/ca...1993091114.pdf

[macona]

I dont think so. Even the old spark plugs from aircraft tended to be multiple gap designs.

[Bguns]

3/4 and 1/2 Pipe was VERY Common right out of the Factory..

Many Early Plugs were Metric, which in those days, would have not been Popular in Mid US.... Not as much Equipment to cut those Odd Threads

1908 is just a bit early for a Sparkplug on a one Cylinder Engine.. ( They were used, but just not as much as later). On a Foos (have seen several) it was usually a low tension Coil Ignition with the Points located In the Combustion Chamber. Many Engines were converted. (with Factory add on kits to remove Points and install a blank Plate Threaded for Spark Plug) An option was also a Possibility, depending on what customer wanted. A High or Low Tension Magneto was expensive, and Dry cells were cheaper (At least for a while..)

The points were actuated by Exhaust Valve Push Rod and insulated from Ground by Mica Washers to seal combustion gases. (Needing frequent cleaning...) External screwed in plug was simpler (And Mainly Cheaper )

That plug does look shopmade, and Brass is easier to machine, and strong enough for the job..

[wierdscience]

Nowing a little about hit'n miss engines there is a good chance it could be years before a plug would be pulled.
My Fairbanks Morse Z was like that,pipe threads and brass.The rest of the engine was stuck solid,but the plug came right out.

[John Stevenson]

Early plugs were metric threaded as the German plugs had the better technology and by the time the UK and the US had caught up the standards were set.

Ford tried to reverse this with gas threaded plugs but he was too late to make much headway although I do believe the Model T has these gas threaded plugs fitted.