Wrong plugs?

[Guest Oldie & Goodie]

Changed out the spark plugs for the 1st time in our Roadmaster. Manual calls for a AC-46 but they don't exist except on eBay, so I went with a AC-45. The ones that I removed were AC-43R. They were really carbon fouled to the point that 2 had almost no gap space.

Is the carbon buildup a result of the plugs not being hot enough or do I have other issues I should be checking on?

[NTX5467]

The "43" heat range plugs are three notches colder than the factory spec'd plugs. This can explain the carbon accumulation somewhat, but if the carburetor is running too rich (from too much automatic choking and/or not enough run time for things to fully warm up), that can make it worse.

The "45" heat range is just one notch colder than the stock spec. If everything else is working good, it should generally work fine.

The best gauge would be to install the "45" plugs and then drive the vehicle on the highway for a good while. It might take some time for the fresh plugs to fire things off well enough to get the carbon accumulation cooked out, though. Then, when things cool down, pull a few of the plugs and look at the center electrode and ceramic insulator. There should be little, if any, carbon accumulation with the ceramic being a "neutral" color.

Be sure to set the plug gap to specs!

Enjoy!

NTX5467

[Guest Oldie & Goodie]

Thanks for the information and I'll be sure to follow your suggestions once I'm able to get her out on our NY roads. Thought spring had arrived but the snow fairies had other ideas.

[Guest Jim_Edwards]

The "43" heat range plugs are three notches colder than the factory spec'd plugs. This can explain the carbon accumulation somewhat, but if the carburetor is running too rich (from too much automatic choking and/or not enough run time for things to fully warm up), that can make it worse.

The "45" heat range is just one notch colder than the stock spec. If everything else is working good, it should generally work fine.

The best gauge would be to install the "45" plugs and then drive the vehicle on the highway for a good while. It might take some time for the fresh plugs to fire things off well enough to get the carbon accumulation cooked out, though. Then, when things cool down, pull a few of the plugs and look at the center electrode and ceramic insulator. There should be little, if any, carbon accumulation with the ceramic being a "neutral" color.

Be sure to set the plug gap to specs!

Enjoy!

NTX5467

I hate to raise this prospect on the "carbon" buildup on the old plugs, but it could be from worn, hard, and cracked valve stem seals or even valve guides. Always a good idea to keep an eye on what comes out of the pan when changing oil before chunks of valve stem seals clog the oil pump pickup.

Jim

[old-tank]

The first time I bought plugs for my 55 after AC44 was no longer available, I was sold a set of AC R43S which fouled in 20 miles....even though that is only one heat range colder. None of my old iron likes resistor plugs or resistor wires. Autolite 75 is a non-resisitor plug that will substitute for the AC44 which may still be too cold for your car.

Willie

[Guest Oldie & Goodie]

I hate to raise this prospect on the "carbon" buildup on the old plugs, but it could be from worn, hard, and cracked valve stem seals or even valve guides. Always a good idea to keep an eye on what comes out of the pan when changing oil before chunks of valve stem seals clog the oil pump pickup.

Jim

First thing I did last year after we got it home was to change the oil. Never thought to check to see what else might have been in the pan. Next time I'll know better. Thanks.

[Guest Jim_Edwards]

First thing I did last year after we got it home was to change the oil. Never thought to check to see what else might have been in the pan. Next time I'll know better. Thanks.

Getting back to the carbon on the plugs issue, there is also the distinct possibility the coil has become weak. If the original coil you might want to check it for correct resistance as specified in the service manual. A weak coil will not provide enough energy to completely burn all fuel entering the chamber and certainly not any oil that might be seeping in via valve stems. If using correct or near correct A/C non resistor plugs stick with an A/C coil. All plugs are not created equal, though supposedly a direct substitute. For example; chances are an A/C coil, even if brand new, will not produce sufficient output to correctly fire an Autolite or Motorcraft spark plug. On the other hand an A/C or Champion plug will likely suffer premature ceramic breakdown and blistering with a Ford coil. Keep in mind individual ignition systems were designed to work properly with the originally specified coils, points, wires, and plugs. Alter one and it's a good idea to alter all with compatible components. The exception being substituting a Pertronix Ignitor II for points. A good idea for all points ignitions, but be sure to use the matching coil for best results.

Jim

[NTX5467]

On the issue of ignition coils for older vehicles . . . when I needed one for a GM car we have, I ordered up an ACDelco coil. When I openned the box, I expected to find a ACDelco-logo'd item. What I found was a generic-looking mostly-flat-black coil with no identifiable markings, other than a production code stamped into the bottom. NOT what I expected.

Further research indicated that that was all that you could get, about 15 years ago, even if you ordered the correct ACDelco item, or the same one as you might have purchased before that. That led me to believe that they (at that time) were sourced "off-shore" and might not be the exact match which was desired. I might be doing something wrong, but I've not been able to accurately (from what I can tell) measure the resistance of an ignition coil. I know, it should be pretty straight forward, but when I do the numbers don't come out anywhere close to what the service manuals claim. Therefore, I've continued to use existing production coils with no problems. Be that as it may.

As for "resistor" plugs, the added resistance should make the coil build up more energy before it fires, just as the internal gap in the old Champion "commercial" plugs did, or a wider gap between the rotor and distributor cap would. AC also had some "commercial" plugs, which were designed more for city delivery truck-type use, but would work in normal driving. Back in 1964 (or so) when Champion had the two Cadillacs on the drag strip, one with AC plugs and the other with Champions, the particular Champions were later determined to be the "commercial" plugs, so the coil would have to build a hotter spark to fire the plugs. The Champion-equipped Cadillac consistently won.

I ran across the issue of electric energy consumption by spark plugs a few years ago. Seems that NGK plugs had the lowest energy consumption, lower than the OEM brands. In any event, sparks jump easier between clean and sharp surfaces . . . but ONLY ONE with each spark, unlike some of the multi-electrode plugs seem to imply.

I know there are people who always claim that you should use the same OEM plug brand as the vehicle came with. This can be good "default mode" orientation, but it might also be true that another brand of spark plug can work just as well, if not better, than the OEM. In the case of many late-model Buick V-6 spark plugs, what's in the ACDelco container is an NGK or Nippondenso spark plug with ACDelco part number identification on it, the particular brand depending upon the model year and engine version--been that way for about 10 years. I've had much better service from Motorcraft plugs in my Chevy small block V-8s, which surprised me as they held up longer than similar Champions had . . . even in the earlier 1970s. After I discovered the NGK V-Power plugs, that's what I've used (the same style plug is OEM with Toyotas, but the same heat range also crosses into a 1980 Chrysler 360 2bbl application.

In the case of older spark plugs for vintage vehicles, sometimes it's necessary to play around and see what might work for the engine/vehicle application you have. Nothing wrong with using ACs, but if you can't get them (anywhere or at a reasonable price), then shopping to see what's out there might be in order. Or possibly seeing if a more modern "fine wire electrode" platinum or Iridium plug might also work, which would have lower energy consumption and have a "basically forever" lifespan in a limited-driven vehicle.

In reading various vehicle blogs over the past years, there are some definite orientations of which brand spark plug might work best in which engine. All of these comments can be valid, but can also relate to what's easily and readily available in the particular market area AND at which auto supply/discount house. I know what my own experiences have been with AC, Motorcraft, and Champion in stock engines. I also know that when I got up enough nerve to spend $50.00 for a set of Split-Fires (back when they were highly-touted), they did not perform any better and didn't last as long as the OEM brand plugs did. So I got my old NGK V-Powers out, cleaned them up, and reinstalled them.

These are my observations and experiences, your's might vary, which I understand and respect. A spark plug might just produce a spark to ignite a fuel/air mixture, but there sure can be some significant differences in the ultimate outcomes of that simple action!

IF you can find a repair shop which has a tune-up machine with an ignition scope, then you can hook your vehicle up to it and watch the ignition system in action. The height of each of the spark plug voltage spikes, the width between them, and do all of this on a horizontal scale or as a composite display. Plus see how they each change with increasing rpm or as you might carefully load the engine against the foot brake as rpms are slowly increased. It can be quite interesting and informative!

Enjoy!

NTX5467

Edited March 23, 2011 by NTX5467 (see edit history)

[Guest Jim_Edwards]

Great insight! And you are right, my statements were based upon my personal experience and observations over fifty some odd years. My statements about keeping things in accordance with original specifications were intended to simply be advice for those who ordinarily might not have years of turning wrenches and busting knuckles and just need a good functioning ignition system for the limited use our old vintage cars see.

We both should have mentioned plug wires and the need to periodically replace with a proper set for the vehicle. If I had a nickle for every set that bled off from jacket deterioration I'd be getting close to rich. Nothing like firing up an engine in total darkness and watching all the shorts in old plug wires. Can sometimes look like twinkle lights on a Christmas tree though no distinct miss is noted. Not good! Also a good reason to run the wires in proper looms to prevent leakage from grounding against anything. Also, low price plug wires are one of the worst investments one can make.......born to fail!

Jim

Edited March 23, 2011 by Jim_Edwards (see edit history)

[Guest Oldie & Goodie]

We both should have mentioned plug wires and the need to periodically replace with a proper set for the vehicle. If I had a nickle for every set that bled off from jacket deterioration I'd be getting close to rich. Nothing like firing up an engine in total darkness and watching all the shorts in old plug wires. Can sometimes look like twinkle lights on a Christmas tree though no distinct miss is noted. Not good! Also a good reason to run the wires in proper looms to prevent leakage from grounding against anything. Also, low price plug wires are one of the worst investments one can make.......born to fail!

Jim

Right on the mark about the plug wires. As I was changing the plugs I noticed each and every wire had more splits & cracks than I could count. My new wires should be arriving anytime now.

[NTX5467]

Good point on the plug wires!

I inherited a '70 Skylark Custom 2dr ht from my Great Aunt. The car was purchased new in Los Angles and lived its whole life there until we drove it to Texas. She had a mechanic that took care of it for her. Her, myself, and my mother all loaded into the car and came to Texas in it. I had not idea what sort of adventure I'd volunteered for, but there was no turning back.

As we headed south to San Diego, I noticed that the car had a lean surge at 60mph, but not at 62mph. I didn't want to have a chance meeting with any CHIPs, so I did what I could to s tay as close to legal as I could. Throughout the whole trip, the car ran flawlessly. Started on the first crank every morning, and we came to TX in July, with the a/c blowing cold, getting about 17mpg or so. It was an uneventful trip, which was good!

After I took possession of the car a few years later, I went over it to see what was what. I found, basically, original plug wires on the car. All were brittle, so I ordered up a new set of pre-built magnetic suppression wires for it. The spark plugs looked a little flaky, so new ones were installed. I never did rebuild the carb as it ran perfectly. What I found which somewhat preplexed me was what appeared to be a variable vacuum bleed with "CARTER" on it--never knew of such, and had two electric wires going to it, being plumbed into one of the smaller vacuum source take-offs on the base of the carb. I removed it. The OTHER thing was a stack of California Emissions Inspection "Pass" documents. Even with these things, it seemed to never fail the CA emissions tests.

Take care,

NTX5467

[Airy Cat]

I use Autolite plugs in my Buicks with good results. Autolite #75 & #76.