Autolite 2245 thread size?

trev · Post by **trev** » Mon Dec 11, 2017 7:38 am

Looked through ORD 9 SNL G758 for the Autolite 2245 spark plug thread size on the plug wire end, but only found the info below. I mucked up a couple threads and would like to clean them up.

"PLUG, spark, shielded, 14-mm, is/(6 hex, 35/si overall 4 (radio suppression wtrprf type)"

radtech · Post by **radtech** » Mon Dec 11, 2017 12:25 pm

I looks like 5/8x24

Post by **wesk** » Mon Dec 11, 2017 2:21 pm

One must be carefull not to use standard metric taps on spark plug to cylinger threads. The actual 14mm plug thread is considerably smaller than the nominal 14mmx1.25 standard fine thread.

The easiest clue to the top end thread size of the plug is the parts manual ORD 9 SNL G-758 where you were already but just look at the page for the plug leads, page 151, last item on the page.

https://en.wikipedia.org/wiki/Unified_Thread_Standard
Thread specs

http://www.rjmann.com/pdf%20files/stitt ... sories.pdf
Good source for the lower end plug thread tools.

radtech · Post by **radtech** » Mon Dec 11, 2017 6:27 pm

You can get a die for 14mm spark plugs at many auto parts stores.The threads on the top of the plug are 5/8x24.14mm spark plug dies are common as are the taps.

trev · Post by **trev** » Mon Dec 11, 2017 8:16 pm

I was close... Much appreciated info, thank you!

Post by **wesk** » Tue Dec 12, 2017 2:48 am

I have to disagree with Radtech:

1-Spark plug lower threads are not nominal they are slightly smaller then nominal and require a spark plug thread size IE 12mm, 14mm, 18mm specific tap or die. An example is the nominal 14mm-1.25 tap will cut a thread that will fit the plug loosely. The special spark plug 14-1.25 and the correct drill size for it will leave a tapped hole that fits the plug tightly.

2-The upper barrel thread size is 5/8-24NEF-3 however the M38A1 ORD 9 shows 11/16-24NEF-3 which is too big.

trev · Post by **trev** » Tue Dec 12, 2017 7:55 am

11/16-24 is a little loose, UNEF is comparable to NEF-3 correct?

Post by **wesk** » Tue Dec 12, 2017 11:11 am

Yes. I never tighten those spark plug shield nuts more than wrist snug. Overtorquing will crush the end of the barrel and damage the nut threads on the next removal.

On the loose issue note: I am quoting the M38A1 parts manual thread size which reads 11/16-24NEF-3 for the nut PN 7528187.

The M38 ORD 9 lists the 7528187 nut thread size as 5/8-24NF-3.

So the next step is to try the 5/8-24NF die for fit.