AC K10 spark plug --- modern equivalent

[scott12180]

Packard service literature in the early 1930's recommends AC spark plugs---  type K9, K10 or K12 for my 1932, depending on the heat range.

 

I've yet to find a list of what the modern designation for these plugs would be. 

These are 14 mm plugs but what's important is the heat range ---   K9 is cooler, K12 is hotter --- and especially the reach into the cylinder.   

I'd like some NOS plugs.  Nothing much on eBay. . . .

 

Any suggestions?

--Scott

[cahartley]

Here's a whole load of 14 mm plugs.

You can get a good idea of how hot or cool they are by the length of the insulator.

 

http://www.speedwaymotors.com/shop/oval-track-spark-plugs~142-2-10-568-7212

[Bloo]

That old AC numbering system went away I believe in 1937. I dug deeply trying to figure out what was equivalent to the K-7 recommended in the 1936 Pontiac shop manual. There is no good cross reference, but the best clues are in old postings on this site by user "mlander". I imagine I am telling you what you already know, as you are in some of those threads. "mlander" last posted here in 2006. The K-7 turned out to be about an AC-45. I also found an application chart from the 40s somewhere that backs that up.

 

All I can offer is that if you are looking for K-9 to K-12, those are really hot. I would just get the hottest one offered in that size.

 

http://forums.aaca.org/topic/97942-spark-plugs-for-a-1932/?tab=comments#comment-421927

http://forums.aaca.org/topic/87501-old-ac-sparkplug-chart/?tab=comments#comment-372303

 

[Owen_Dyneto]

Try Autolite 303, that's what I have run for many years in my '34 Packard Eight, that plug performs perfectly in my engine.  Also Autolite 308 a possibility.

[scott12180]

With your suggestions, I've discovered these cross reference charts.  None of them cross the old AC nomenclature (K9, K12) to the new (46, 47, 48) but they might be useful for other brands.

 

http://graylady.atwebpages.com/sparkplugs.htm

 

http://www.oldengine.org/members/diesel/Plugs/equiv.htm

[scott12180]

Does anyone know in the AC sparkplug nomenclature, what an "X" suffix means?

 

What's the difference between an AC 48 and 48X?  or AC 46 and 46X?

I haven't found any explanation,  yet.

 

--Scott

[Dave39MD]

In an old car AC catalog they show the plug 46 for 31-36 Packard's with 14mm plugs.  46 was a non resistor and discontinued many years ago, replaced by R46 which is a resistor plug that helps with radio interference. R46 is not available either but can be found on ebay once in awhile. The currently available plug is R45, slightly cooler than the R46.

X stands for special or wide gap.

 

Dave

[Bloo]

the LM46  is still available, same heat range in a lawnmower plug. The insulator is shorter. The top doesn't unscrew. For what its worth, the old AC plugs apparently were shorter in height than the current ones . Heres a KL7 and an LM46:

 

[scott12180]

Interesting. . . .

" X stands for special or wide gap."

So on an AC 48X, the electrode gap is wider than on a 48? If that's so, couldn't you just  make the gap whatever width you wanted it to be?  Why the special designation? 

 

Also, anyone hear of a Prestolite spark plug?

What's in the Packard now are Prestolite 147's.  I'd like to find out what heat range they are because they appear to be too cold. The only cross reference I can find is on sparkplug-crossreference.com which suggests they are about like an AC 45. If that's true, then I do want a hotter plug, like AC 47 or 48.

[Dave39MD]

Prestolite 14 7  crosses to AC 45. I would ask the men who own them what they are using, is there a Packard forum?

 

On the wide gap the side electrode is longer and more able to withstand a wide gap. They started being used a lot when HEI (high energy ignition) came out.

 

Dave

 

Edited August 16, 2017 by Dave39MD (see edit history)

[edinmass]

AC plugs have been hard to get for a long time in the pre 1937 nomenclature. I just acquired a set of eight recently, (last month) and you dont want to know how much I have in them. They are going on our Pebble Beach car this week. The ultimate in details to compete in the stratosphere. These are the factory called for heat range, hotter plugs would be better for today's modern fuel. I would like two more sets for V12's.  I would run Autolite for a modern plug. My best, Ed

[Grimy]

10 minutes ago, edinmass said:

I just acquired a set of eight recently, (last month) and you dont want to know how much I have in them. They are going on our Pebble Beach car this week.

Ed, I hope they work well for you--the old plugs are the ultimate detail.  But in the last couple of months of the Cadillac and LaSalle Club's magazine, the tech editor tested NOS AC plugs with a >75% failure rate right out of the box.  He attributed the failure to the sealing materials and technique used on the porcelain.  So I recommend you be prepared with Brand X of your choice for the Tour (see you there) and perhaps save the NORS ACs for Sunday judging.

[Bloo]

2 hours ago, edinmass said:

I just acquired a set of eight recently, (last month) and you dont want to know how much I have in them.

 

Ed: Thank you for posting the picture. I suspect it is the only one of an AC K-7 on the web. Any chance of a close up of one plug? How tall are they? Are they 13/16 hex?

 

 

 

 

 

 

Edited August 16, 2017 by Bloo
.. (see edit history)

[Frank DuVal]

I posted this in the Buick forum recently.

[edinmass]

The chart appears to be post war.

[edinmass]

Bloo.......the plugs are installed in our car, and it's at Pebble Beach. We are in the Packard class. I'll take a few photos tomorrow while we are detailing it. 

[Bloo]

Thank you!

[Spinneyhill]

Here is a K-10.

https://picclick.com/Single-Antique-Vintage-Ac-K10-Spark-Plug-112473347433.html

[Larry Schramm]

Looks like a modern AC-45.  Would need to see the insulator tip to be sure.

[Spinneyhill]

1 hour ago, Larry Schramm said:

Looks like a modern AC-45.  Would need to see the insulator tip to be sure.

I think there is a photo of it on the link.

[Bloo]

6 hours ago, Spinneyhill said:

Here is a K-10.

 

Thanks! I followed that to an auction and there were several more pictures. Look at how much taller the metal part looks than edinmass's K-7. Apparently they accommodated the longer (hotter) insulator that way.

 

Larry: here's the tip.

 

 

Edited August 17, 2017 by Bloo
.. (see edit history)

[Frank DuVal]

It is a post war chart. Posted to help with the 48X and LM series questions.

[scott12180]

On 8/15/2017 at 8:13 PM, Grimy said:

But in the last couple of months of the Cadillac and LaSalle Club's magazine, the tech editor tested NOS AC plugs with a >75% failure rate right out of the box.  He attributed the failure to the sealing materials and technique used on the porcelain. 

Could someone  post the article or post the details of this test  which resulted in more than 75% failure on AC spark plugs? 

I'm not a club member as I don't own a Cadillac-LaSalle, but I am very interested in how the test was done and which spark plugs were effected.  I think we all could benefit from these results.

Thanks

[Grimy]

Scott, I'm pretty sure the material is copyrighted, but you might contact the author, John Washburn, at

johnDOTwashburn47  AT  gmail  DOT  com   I corresponded with him on his series on problems with NOS condensers, and he was willing to help.

[cahartley]

NOS condensers are like year old bread.

They are all dried out but make nice ornaments.......if you enjoy looking at condensers....... 

[Larry Schramm]

On ‎8‎/‎18‎/‎2017 at 10:29 PM, scott12180 said:

Could someone  post the article or post the details of this test  which resulted in more than 75% failure on AC spark plugs? 

I'm not a club member as I don't own a Cadillac-LaSalle, but I am very interested in how the test was done and which spark plugs were effected.  I think we all could benefit from these results.

Thanks

 

Having made millions of them while going to school,  I would like to see the testing and failure mode.  Also would like to know what the definition of "failure" is.  Does not sound even closely real.  Maybe 1 in several thousand plugs, but not 75% failure rate.  Baloney.

Edited August 22, 2017 by Larry Schramm (see edit history)

[edinmass]

Pebble has come and gone. We had a good time and a great car on the field. Here are some photos of the car on the field. Included is a shot of the engine with the plugs installed. The car started and ran fine. All the plugs were good. Ed

[mikew16165@aol.com]

I have some NOS AC K-12 if you need them

On 8/14/2017 at 10:11 PM, scott12180 said:

Packard service literature in the early 1930's recommends AC spark plugs---  type K9, K10 or K12 for my 1932, depending on the heat range.

 

I've yet to find a list of what the modern designation for these plugs would be. 

These are 14 mm plugs but what's important is the heat range ---   K9 is cooler, K12 is hotter --- and especially the reach into the cylinder.   

I'd like some NOS plugs.  Nothing much on eBay. . . .

 

Any suggestions?

--Scott