If I decide to use the 14mm plugs (with the adapters), any thoughts as to the "right" ones to use?
I want to be sure the electrode gets down nearly as far as the standard 1/2" MPT plugs do.
Not trying to convince you otherwise, but why would you not just use the standard plugs? Unless you're using original Champion X plugs, There's only one set of threads to seal up with regular plugs instead of two when you screw a plug into an adapter.
I hope I didn't just start another one of those fights about taboo topics. I've just never understood the reasoning and would like to hear the pros and cons.
I find that standard 1/2NPT plugs work fine. The only reason I can think of to use the adapters is if you wanted to use a different heat range plug or that the threads in the head are messed up and you can better seal using the brass adapters.
It's getting harder to find non-resistor plugs and what I have found is, if you are running coils, the resisters don't like the voltage spikes and don't seem to last long.
I use 14 mm plugs because of the many available heat ranges. But I have a highly modified engine in the 50 horsepower range and get better tuning with them. If you are using the original Ford magnifying glass for ignition and the Mason jar with a wick in it for a carburetor you can light the mixture off with a regular Ford spark plug. Oh yes and be sure to adjust your valves using piston position so you can throw away 025" lift and drive more slowly.
When I bought my used Z-Head it was set up for 14 mm plugs. Initially I had fouling problems. The fix was to use the hottest plugs I could find. It runs fine now.
"I want to be sure the electrode gets down nearly as far as the standard 1/2" MPT plugs do."
Keep in mind that factory X plugs made for high heads (type A-25) were longer than X plugs made for low heads (type A-15).
Many years ago I switched to a Z head and had the same decision to make. I drive the car but don't "show" it. I wanted to have the wide variety of inexpensive 14 mm plugs available. So I figured the decision was made.
Then I got to thinking about how soft aluminum is and that I often use the spark plug holes to fit a pair of eye bolts for lifting the engine. The 3/4" pipe threaded holes started to look like a much better idea.
Next I looked at the adapters for reducing 3/4" down to 14mm. The problem with that was the cost, which I can't remember how much it was.
My solution was to get the 3/4" hole head for safety in engine lifting and to make my own adapters... VERY EASY to do and very inexpensive. Just get 4 bronze 3/4" reducers from the hardware store and drill them out and tap them for 14mm plugs. Put them into the head and forget them. I have used them for about 15 years and they work great. You can cut them down so they don't protrude into the chamber if you need to. If you ever cross thread a plug, shame on you! No problem just throw away the insert and make a new one.
1/2 inch, not 3/4 pipe thread
Eric, I think you are right. If I remember correctly you need a ½" X ¼" reducer.
I done that same thing as Terry
They work good I gone back to standard to
plugs why because I found a set cheap
Still have my 14mm plugs Bosch 405 long reach this threaded top
I made brass thumb nuts that go on top and brass collars "from restoration supply" this makes then look old timey
I can now confirm that you want to use 1/2" reducers as Erich states.
I use the same reducers to make my lifting eyes also. I drill them out and insert a FORGED eye. Then thread a bolt on and weld it to the eye making sure the eye can turn in the reducer. Next I grind back the nut so that it clears the threads and does not bottom out on the block's deck.