VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1929-1932 2-part spark plugs

Hi Gang,
My '30 Chevy has Champion spark plugs that are in two parts: One bit that screws into the head, carrying the ground (earth) electrode, and a second bit that screws into it carrying the insulator and central electrode. Both parts are pressure-sealed by Cu washers.
On the back floor, I found another set of <used> plugs that are of one-piece design.
Originality is not my quest at this point, especially for normal-wear components, but what is the 'best' replacement plug?
Comments appreciated.

Rick

The best replacement plug for your car is AC-C86.

See Rick - I told you this guy was good!!!

JYD , Who sells those AC plugs and are they $11.00 each? OOPS! sorry wrong model year, I need plugs for a '28 I have a good looking new Champion plug for $4, since D.B . never sent those A/C's to my favorite charity:
MrMack's Ministry LLD. Inc. La De Dah. AKA Brother Chevy Loves' Starvation Show!

:love:

The correct spark plug for the 1928 is the AC 78S and only the OLD version and not the new. The original plug was a 3/4 reach and the new one is only 1/2. So look for the old ones which are usually available at swap meets.

I guess that is why the guy sold me the Champion plugs he said something about them having the proper reach and that the A/C replacement didn't! ( and he usually knows what he is talking about, he is a native Texan) It sure runs good with them. I gapped them to almost 40 thousandths

The AC-C86 plugs for the 1929-32 engines are available on order through your local auto parts store, or you can get them from the Filling Station as well. They sell for $2.75 each.

Ray,
What about the AC 78 or 76 spark plugs for 4cyl. Chevy's

Hi chevy b,

Suggest you go to the 12-28 department and read the comments by pre25chevy4. :p

As to the AC 78 and 76 spark plugs, how to read a plug is in order.

1. AC-Delco of course specifies the manufacturer of the plug.
2. The 7 indicated that the plug is 7/8 thread size. (That is compatable with the Chevrolet 4-banger)
3. The 8 or 6 (second digit) indicates the heat range on a scale of 0=cold to 9=Hot.

The AC-Delco spark plug catalog lists the AC C77 as the recommended plug for the Chevrolet 4-banger all years. Now we have a new digit interjected and that is the prefix letter C. C=commercial :p

However, the key to the plugs used in the 4 cylinder cars is they must, a) have 7/8 threads, b)have 3/4 reach or longer, and c) be at or near the desired heat range. (Which is about an 8)

Why do we need a plug with 3/4 or better reach? Because the threads are much deeper in the heads of the 4 cylinder cars. If a plug of only 1/2 inch reach is used for any period of time the unused section of threads will be damaged and any attempt to install a longer reach plug will require the threads to be "chased".

What is not mentioned here is other brands of plugs. Any brand will work that meets the specifications above.

On the correct application for spark plugs, a technical advisor once told me that "If it will screw in.....it will work!". Well, I don't know about that as far as vintage cars are concerned, but that would make one heck of a cool slogan to put on a "Tee" shirt!!! :eek:

JYD, there is a lot to be said for that "Tech Advisor" ....If it WON'T screw in it may not work too well! Oh something I have learned here ,sometimes it is better to only give a Generic or partial answer, and let the question asker do the research and work. makes better troops out of them.

I just wanted to chime in about "If it will screw in, it will work." That is a fine statement if you're talking shorter a reach, but watch out if the reach is too long.

Dan.

On the topic of spark plugs my original Canadian owners manual states AC Metric 140 spark plugs for 1929 Canadian models. Where can I find those??????

According to ones who <might> know, the AC Delco part number, C86 means:

C = Commercial
8 = 18 millimeter
6 = 6 on the heat range scale, just above average (5).

No indication as to reach.