Green markings on AC spark plugs

[Roy B.]

Re: Green markings on AC spark plugs

here's some info I was able to glean from TDB posts and my own investigation:

Type 1 AC plug (53-57) no green bands and lacks circular ridges on the ceramic tower.
Type 2 AC
Type 3 AC plug (60-74) 4 thin green bands over circular ridges on ceramic tower.
Type 4 AC plug (75-?) three thin and one thick band on top of circular ridges.


I came up with the 74/75 years because I inquired about some plugs and a box that was marked 1974 had the 4 thin lines, while one marked 1975 had the three thin and one thick... What do you think?

Type 1 AC plug (53-57) no green bands and lacks circular ridges on the ceramic tower.

I ten to agree with you , some one should do an articial

[Troy P.]

Re: Green markings on AC spark plugs

Taking this one step further, when did the box change from the blue and orange to the blue and white?

[Ian G.]

Re: Green markings on AC spark plugs

It would be good if we could get the info up to the latest model the NCRS allows, which is what, 1993?

[Mike E.]

Re: Green markings on AC spark plugs

For what it's worth--
I have an original blue and orange AC spark plug box with AC44 on it. In it are 8 individual small blue and orange boxes with 44 on it, and the date on the flaps on each of the small boxes is 58.
Inside each box is a used AC 44 with 4 white ridges in the ceramic, with no green lines. I do not know the history of these other than they came from a closed down service station. I would surmise that in 58 the plugs were changed, and that these are 56/57/58 vintage plugs, but I cannot tell you that with absolute certainty.
There are six patent numbers on the bottom of the large box--I suppose if I was really enterprising I could look up the latest of them, (2,760,875) and find out when that patent was granted, but that would only give me a date prior to which the large box could not have been produced.

[Mike M.]

Re: Green markings on AC spark plugs

What is your brand? Aren't you an MD?

I enjoyed the el cheapo Xmas story by the way.

Levi, yes, glad the story got a chuckle out of ya.mike

[Troy P.]

Re: Green markings on AC spark plugs

Here's some more info on the NOS plugs and boxes on my shelf.

I have 44-5's in boxes marked '56 and some marked '58. None of these plugs have ridges or stripes. So maybe the ridges didn't come out in '58 or they came out sometime during the year but not at the beginning?

These plugs are correct for '53-'55 and possibly later years. I note the boxes have 8 plugs indicating an 8 cyl application was envisioned in addition to the 235 engine. Parts book indicates they would be correct for the '55 V-8 too.

[Gary C.]

Re: Green markings on AC spark plugs

Mike and Troy,

Mike - patent # 2,760,875 was issued 8/28/1956
Troy - learned today that plugs with dashes in the number such as AC43-5 ceramic is straight and do not have ribs. The AC43-5 which was one of two plugs listed for '56 in the 1st and 2nd edition Owners (Instruction) Manual and '57 3rd edition, the other was AC43. 4th edition '57 Owner's Manual spark plugs were AC43, 44, 46 and 42-1

For what it's worth a Tri 5 Chevy guy told me that the ribs were added to keep the V/8 engines spark plug boots on.

Still looking for AC43, 44 and 46 in '56 & '57 dated boxes to confirm they had four ribs.

Appreciate everyone's input. Merry Christmas, Gary....

[Jeffrey S.]

Re: Green markings on AC spark plugs

One of the ways to confirm dates of different configurations is by resaerching AC sparkplug advertizing. I have ads from almost every year from the 50's and 60's. The ribbed plugs were first used (and advertized) in 1956. They had no green on the ribs and were trade marked "Hot Tip". As was posted earlier, the earlier plugs had smooth porcelain and were trade named "Corolox". These were available in GM cars with 14 mm threads and standard heat ranges and half heat ranges and designated for example "44" which indicated a "4" heat range and "44-5" which indicated a 4 and 1/2 heat range. In 1960 the green rings appeared and were trademarked "Fire Ring" . The ribbed plugs did not have 1/2 heat ranges but a 1/2 step up in heat range was accomplished by extending the tip and designating with an "S" suffix (45S). The 4 thin rings lasted until about 1973 when the top ring and rib was thick and the others were thin. Much more recently the green again was removed but the rib configuration remained the same. Others may have more info but this iwhat I have been able to learn from my research.
Jeff

[Gary C.]

Re: Green markings on AC spark plugs

Jeff, thanks. John Hinckley told me you're the man on AC spark plugs. Also a picture of the first FI engine is in Ken Kayser's book on page 202 and it shows 4 ribbed no paint plugs. Appreciate your clarification. Stay warm up there! Gary....

[Gary C.]

Re: Green markings on AC spark plugs

'56-7 spark plug chart attached. Appreciate review and comments. Thanks, Gary....

[Troy P.]

Re: Green markings on AC spark plugs

Jeff, what do you think about the "dates" on the boxes we're finding of Corolox plugs going into '56 and '58? I understand your assessment is that the ribbed plugs were out by '56. Is it possible what we think are dates on the boxes are not actually dates?

[Clem Z.]

Re: Green markings on AC spark plugs

the ribs were added to give a longer path on the outside of the porcelain to prevent the arc over.

[Jack H.]

Re: Green markings on AC spark plugs

Right you are! The rib technology is well known within electrical engineering power transmission circles. You'll see the ceramic insulators used to hold overhead power line wires designed this way and its purpose IS to thwart arcing by raising the impedance characteristics of the path to ground relative to a flat/smooth ceramic surface!

On the running changes in spark plug's ceramic, this is my understanding:

Type 1, up to 1957, smooth/flat white ceramic.

Type 2, 1958-59, ribbed ceramic without green accents.

Type 3, 1960-69, ribbed ceramic with 4 thin green accents.

Type 4, sometime in the 70's, ribbed ceramic with 3 thin green accent bands and one (top) THICK accent band.

[Clem Z.]

Re: Green markings on AC spark plugs

[Right you are!] now if i could only get mrs clem to say those words once in a while things would be rosie

[Jeffrey S.]

Re: Green markings on AC spark plugs

Troy:
AC still made the smooth porcelain "dash" plugs until 1962 (about). The AC application book dated March 1962 still showed them as active parts. while the March 1963 guide does not show them under any application so sometime in 1962 they were discontinued. I would bet that if you look at the picture on the boxes dated after 1956 you will see the plug illustrated has the ribs and is called "Hot Tip" even though the plug in the box and the designation on the end is 43-5 for example. In addition, some of the very earliest ribbed plugs still had the "Corolox" trade mark on the porcelain and the later "dash" plugs did not so you can see that there was a great deal of flux in those years. It is also important to remember that the dates on the boxes are for the date that the box was printed NOT the date the plugs were made. Of course they should be close but you don't think that AC (GM) threw away any plugs kept in inventory. If they had them they boxed them up and sold them. Based on the documentation I have, The Corvettes coming out of St. Louis did not use the "dash" plugs after 1955. I can't speak to any other GM division or for other makes that used AC plugs (Packard, Studebaker, etc.) I hope this helps. I plan on writing an article for the Restorer on this but I'm sure it won't be published until next summer.
Jeff