scott12180

AC K10 spark plug --- modern equivalent

Recommended Posts

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

Share this post


Link to post
Share on other sites

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

 

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

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

Share this post


Link to post
Share on other sites

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

Share this post


Link to post
Share on other sites

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:

 

KL7-GS.jpg

spark-plug-ac-lm46.jpg

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

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 by Dave39MD (see edit history)

Share this post


Link to post
Share on other sites

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

IMG_4926.JPG

Share this post


Link to post
Share on other sites
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.

Share this post


Link to post
Share on other sites
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 by Bloo
.. (see edit history)

Share this post


Link to post
Share on other sites

The chart appears to be post war.

Share this post


Link to post
Share on other sites

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. 

  • Like 1

Share this post


Link to post
Share on other sites
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.

Share this post


Link to post
Share on other sites
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.

 

Single-Antique-Vintage-Ac-K10-Spark-Plug

 

Edited by Bloo
.. (see edit history)

Share this post


Link to post
Share on other sites
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

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

NOS condensers are like year old bread.

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

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now