Spark plug recommendation 1961 F-134

My username tells it all. I am at the point where I need a new set of plugs. In it were an old set of AC 42FS. I cannot find a cross reference. Any recommendations and what is the recommended gap?

Thanks

 

Ditto for J8C, and yes, they are at the hardware store.

 

:hurrican:

 

ACE Hardware also carries the Champion J8C in their lawn and garden section. The J8 is specified in the factory service manual, the C just denotes a change to copper core, the plain J8 is to the best of my knowledge no longer produced.

 

a note on the J8 plugs-- yes, they will work, but they are NOT long enough!

I know that a J8is what the factory recommends, but something is awry-- I don't know if the changed the design of the plug since then, but they are too short. I noticed this last time I had the head off my f-head. The tip of the plug literally did not protrude all the way into the combustion chamber-- the threaded part of the plug was too short. With the plug installed, there were threads on the inside that the tip of the plug did not reach. The tip was still in the bore of the spark plug hole. From the inside, it looked like someone had not finished threading the plug all the way into the head-- by atleast an 1/8".

With some trial & error with my NAPA guy, I was able to find a plug that allowed the tip of the plug to end where it should (use up all the threads). We found a plug that had the same specs as the J8, but long enough to fit perfectly in the spark plug bore.

the part number I'm using is: Champion L86C

 

good point! also the top of the plug is shorter, old school this denoted the heat range as well, shorter being hotter, longer being cooler

 

Looking at Champion's heat range chart, the L86C is rated 86 industrial heat range which is 12 automotive vs J8C which is 8 automotive, so hotter plug.
https://www.championautoparts.com/Technical/Tech-Tips/choosing-the-right-spark-plug-heat-range.html

I have reached out to an ignition expert I know to see if the plug reach in this case matters, but I think the colder L86C, especially in my application with a mild overbuild F-134, matters most.

 

I just talked with Champion tech support, Hank, is also a mechanic. The L86C is industrial 86 heat range which translates to 12 (colder) on automotive.

The J8C heat range 8 (hotter) is still the same as the original, C denotes copper core. Unless someone can prove otherwise with a NOS. He says with a healthy ignition, increase to .40 gap would be beneficial to ensure complete burn. And there we have it from the "horses" mouth.

 

I tested the J8C between .030 and .040, night and day difference in response/tip in. I was running the L86C at .040 and about the same, but sticking with the hotter J8C's and the .40 gap. Side note, I run non ethanol/pure gas as it combust more completely so YMMV.

 

Then resistor vs non- resistor question. Lol

 

Can you hear the radio if you have one in your Jeep? A non- resistor plug actually fires hotter.
-Donny

 

Autolite 295.