The Stovebolt Site Forums The Shop Area Engine Shop Spark Plugs?

The 59 GMC 370 with 270 6cyl. engine. I want to put a new set of plugs in it. Never had any since I got it and I think I may have fouled one of the old ones by flooding it. I have not removed any, it may have an assortment of plugs in it.
My manual says AC 44 commercial. I have not went to my FLAPS yet, because I want to know what I am asking for first.
Will there be a 44 (commercial) or just a plain 44? Or is there a replacement plug in another brand that would do just as well? Thanks.

Use R44S. The commercial plug had huge electrods for long duration & HD use. The S type extended tip plugs came a few years later & all the manufacturers went to them except flathead engines cannot use them. Plugs last much longer these days as the lead in the gas caused erosion.

The 44 was designed for use in a truck that was at full throttle all the time. I use 45 which is a little hotter for just casual driving.

Thanks guys. This was my first time to hear of a commercial plug. Also my first bigbolt.

The commercial plugs were kind of like the Champion "Truck Plugs" They had a larger ground terminal.

I don't think you can even get the R44 plug in anything other than a tapered seat anymore.

An R43, R43S, R45, or R45s, will more than do the trick for you.

These old trucks ran at a lower compression, plus most modern gas is probably in the 89 octane range due to ethanol and EVP requirements. So, even going with a hotter plug won't hurt a thing.

Thanks much. I think I will go with the R45S with the extended tip. I am using 89 octane with ethanol. Hard to find non-ethanol in my area.

We ran Delco commercial plugs in race engines back in the dark ages. The center electrode and the ground were both heavier material than regular plugs. Those plugs will have a "C" prefix before the number, such as "CR44S" etc. Haven't seen any in a lot of years, but if you find some in a "new old stock" situation, grab 'em! They definitely outlasted regular plugs in a round track engine.
Jerry

Thanks, I will ask all the old parts stores around for some of those.
I am just realizing lots of the old timers wanted those 270 and 302 engines for dirt track racing. Actually the old guy I got my truck from was still a dirt track racer and had collected up all those engines he could find. I think that's the only reason he had this GMC 370, was for the engine.
He showed me a 270 block, that he had someone to use a band saw and cut the motor in half so that they could see something about how the oil galleys ran to the cam or something.
They were trying to improve oil supply to the cam while on the round track. I did not fully understand all he was telling me.

The dirt track racers right after WW II used a lot of 270's from surplus military trucks. Those engines used full-pressure rod bearings rather than the splasher rods in the Chevy, and they were roughly 50 cubic inches bigger. Their problems came on short tracks where they had enough torque to break the rear wheels loose coming off the turns. Dad's 34 Ford coupe with the flathead V8 would be halfway down the straightaway before the Jimmy engine cars stopped spinning their wheels. On a long, high-banked track the GMC's were a lot more competitive because they didn't have to slow down as much in the turns.
Jerry

Great info. Interesting to know about those old engines. In my youth you had to have a V8 to be "in" I never knew 6 cyls. were popular on race tracks. Makes me proud of my old 270.

Jerry, I sent you a PM. I will go ahead and ask the question here:
On e-bay, I just typed in the search: AC CR45S Spark Plugs and came up with a bunch of AC CR45TS plugs. Is the TS the same thing?
Some of them say NOS, but they have TS on them. Are these the same plug that is hard to find? I did not see any that ended in just an "S" Thanks.

T designated tapered seat. They won't work for you.

AC spark plug numbering system.

Thanks much for the info.

cletis: Thanks! That is useful and is a big reason I use this site.

Update on plugs. I got a set of AC- R45S from NAPA. Only cost about $1.70 each.
What a difference !! Starts and runs so much better. Vacuum gauge holds steady in the green at 20".
The old ones looked wet and fouled. They were R 43 without the extended tip.

Hey guys,would AC C44N plugs,
or 46S work?
thanks,
steve sr.

Steve, I am certainly no expert on plugs. But according to the chart furnished by Cletis, the C would be the commercial plug. The suffix "N" shows to be a 9.5 MM thread. So it looks like the c44n would not fit. Think it should be a 14mm.
As to the 46S, that would work. It would be an extended tip (good) but a hotter plug.

Maybe this is a good place for someone to explain to us the reasons for using hotter or colder plugs?
I would think hotter the better, but maybe under hard and constant use, the hotter plugs would soon burn the electrodes. But they would be good for infrequent use and just putting around?
I just know I am well pleased with the R 45 S. And for under 2 bucks each, I could change them every month if needed.

Old GMC Gold,
The way I deciphered the chart was that yes C is for Commercial.
The 1st # is The Thread size.
The 2nd # is the heat range.
And the suffix is different apps.
I E C44N to me now translates to a Commercial grade 14mm threaded plug,
With a heat range of 4.
The N makes it a 3/4 inch reach into the chamber and the Threads are 3/8 of an inch Long.
I know it will fit the head BUT will it stick into the combustion chamber Too Far?
Thanks,
steve sr.

The hot/cold referance is to how much heat the plugs pulls out of the combustion chanber. It isn't that the plug is electrically hotter or colder.
The waterjacket is very close to the threads surrounding the sparkplug, a hot plug will have a small amount of mass and won't transfer heat to the waterjacket - if you look in the end of a 'hot' plug you will be able to see deep inside. A 'cold' plug will have a lot of mass and surface area, you won't be able to look down into one of them, they'll end right at the end of the threads. They pull heat out of the combustion chamber and ito the waterjacket.
The plugs needs only to be hot enough to keep itself clean at idle.
We can change exhaust temps by 150ish degrees by 1 full step in heat range, race plugs can come in 1/2steps for tuning.
You can cool down a warm engine in august with a simple change in the plugs' heat range.

All well and good,
Thanks,
Don,t get me wrong,
But I don,t need a tutorial about what a heat range or mass and such is about.
I know that the C44 will fit and work,BUT with the N suffix is the Question.
All I Need to know is if the C44N plugs will Stick into the chamber Too Far and get Smacked by a piston.
Can catch a deal on a few sets,reasonable,if they,ll work.
Cheers
steve sr.

My mistake,
Should have said for a Stock 235 or 261 application.
Jerry, You there?
steve sr.

I believe the N suffix is going to have a slightly too long thread. If I remember correctly, the 44S plug will have a thread length that just covers all the available threads in the head. If any threads protrude into the combustion chamber they can be damaged by combustion heat and be extremely hard to remove, possibly taking the threads out of the head the nest time they're removed. Stovebolt plugs aren't in much danger of contact with pistons or valves, but unless the thread length is right there can be some nasty consequences down the road a bit.
Jerry

Edit: If the thread length is correct, the extended-tip plug won't cause any problems with mechanical damage. Nothing gets close enough to collide with it.
Jerry

Thanks Jerry,You are a Saint,as always.
Just had to check cause the comm plugs were available and if I could use em I,d buy all he had.
Tempted to buy just a set and measure one up against a say 44 or a 45r thats on hand.
(think box whirling,thinking,eliminate extra thread length)??
regards
steve sr.

A little very careful work with a Dremel tool might work, but be careful not to damage the area where the ground electrode is attached. Pieces of steel bouncing around inside a cylinder can and do make some pretty nasty dents in things like pistons, valves, etc.
Jerry

Agreed, but what I,m thinking,is if the 3/4 inch reach in is after the threads, OK.
The N suffix shows 1/2 the stickin threaded (3/4in or 19mm reach with 3/8ths,9.5mm of threaded length)
Other way round she,s not gonna tighten against the head.
steve sr.

Good point- - - -a picture would help if the seller is willing to provide one. Unless it's an easy conversion, it's probably not worth the effort to try to make them fit- - - -too many "plug and play" options out there!
Jerry

ojh, Thanks for the "tutorial" on spark plugs. I was the one who asked for it. Great explanation. You never get too old to learn something.
BTW, on the old 2 cylinder John Deeres, some people use 2 washers under them, instead of 1. Guess this would take up some threads and move the plug up some.........