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The 1937-38 Super Eight Shop Manual specifies using the AC 103S or the Champion Y-4

In my inventory I found an AC 103 but it looks more like one that would be used in a Crosley.

The middle plug is the recommended AC 103S.

Also in the picture is an AC 106, which is a hotter plug and more readily available on the internet, and I

Yes, the local auto parts stores can get Champion 10mm UY6...

Does anyone know if the UY6 has the same characteristics as the 103S or even the 106????

Any answers, comments or suggestions are appreciated.

Thanks.

Bob

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I don't know the differences offhand, but I'd recommend AutoLite 3136 which should be on the shelf or available within 24 hours at any decent auto parts store. I've used them often with good results in Packards that use the 10mm plugs and it is AutoLite's current recommendation for that year & engine.

PS - UY6 is the heat range equivalent of the M8. 104 is a hotter plug intended for more local and stop/start driving.

AC 103S:
The "10" means 10mm. "3" indicates a rather cold plug. "S" indicates extended tip OR (7/8") moderate long reach (23/32").

I strongly suggest however to follow owen Dynetos advice to use the AL 3136.

According to my amatuer study the Autolite 3136 is a hot plug "6". Non-resistor because of the second "3".
I would much prefer the hotter heat range plug unless i planned to start pulling airstream trailers thru the desert. In which case the colder AC 103S might be better.

The AC 106S would be just fine but a bit hotter than i like. 105S or even 104S should be just right.

Thanks for all the great input!!!!

Now the $64,000 question......

Why are the base/thread sizes in mm and the gaps in inches???

Bob

That is an intriguing question. I was told that the Germans developed the spark plug & that the treads have always remained metric. Any one know better?

I don't know the answer, but not all spark plugs for U.S.-made cars have metric threads. Pierce, Packard, and many others used plugs with 7/8-18 thread back in the late 20s, early 30s, I think some even used NPT (tapered U.S. pipe threads).

AutoLite 3076 is a 7/8-18 threaded plug which was an extremely popular plug in it's time for cars and continued in use for a very long time for truck and commercial industrial engines, check the application list of car makes that used this plug - very extensive.

autolitecatalog.com/PartDetailWindow.aspx?b=A&pn=3076

Thanks, everyone, for all the input.
I appreciated it.

Bob