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AC46 SPARK PLUG ALTERNATIVES


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Hi Guys

 

I was looking for a new set of spark plugs for my 1940 Buick special

 

I called the parts guy and he said he did not have AC46 spark plugs

 

I found a cross reference list below and he had some of them or alternatives his computer pulled up

 

He said some look like small lawn mower plugs some do not

 

some plugs he suggested were

 

autolite 405

 

ngk 3110

 

champion 318

 

what is the correct plug??

 

here is the cross reference  list from the web

 

AC DELCO 46 - Alternative spark plug 

 

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I just pulled one of my spark plugs from the car

 

the plug is a champion RJ12C

 

I did not see it on a cross reference list for a AC R45

 

although I did not see it on the cross reference list is the champion RJ12C also a correct plug for the car?

 

 

 

 

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I saw that it shows up on a cross reference for a AC 46

 

but someone posted the spark plug for the car was an AC R46

 

and it does not show up in that cross reference so I am confused?

 

is an AC R46 correct for the car or an AC 46  

 

 

 

 

 

 

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AC - 46 was what it came with originally, but no longer is made.  The AC - R45 is what many think is the best alternative.  Sometimes you can find original plugs at swap meets or on the internet.

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Though AC46's are rare, they can be found on e-bay now and then.

AC plugs get hotter as the number goes up, so you could use a 47 or a 48 without too much concern.

There is also an AC-C49 which is in production and is used quite often in generators.

 

HOWEVER, if you are running a plug cover, you must physically match the length of the replacement plug to the spec'd AC 46.

Thread depth and insulator height must match also.

 

Ask me how I know............

 

Mike in Colorado

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The R46 is a resistor spark plug, the same heat range as the 46. Resistor plugs incorporate a ceramic resistor to suppress ignition noise generated during sparking. Resistor spark plugs prevent electrical interference that can disrupt car radio reception, two-way radio and cellular phone operation. This type of spark plug also prevents electrical noise from interfering with the operation of the computer in the engine, should your 1940 Buick ever have one installed!

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Posted 15 hours ago

Though AC46's are rare, they can be found on e-bay now and then.

AC plugs get hotter as the number goes up, so you could use a 47 or a 48 without too much concern.

There is also an AC-C49 which is in production and is used quite often in generators.

 

HOWEVER, if you are running a plug cover, you must physically match the length of the replacement plug to the spec'd AC 46.

Thread depth and insulator height must match also.

 

Ask me how I know............

 

Mike in Colorado

 

 

 

Thank you for the tip , I found the original sheet metal covers for the spark plugs in the trunk

 

would the plugs I have in the car (champion RJ12C ) which cross reference with the AC 46 fit in w/ no problem?

 

would the AC R46 fit in w/ no problem?

 

 

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Measuring from the base where the gasket sits on the plug to the tip;

Green Stripe made by AC

R46 - 2.236

44 (should be the same as 46) - 2.236

Currently available ACDelco

R45 - 2.496

Vintage of the car AC

46 - 2.202

 

You can get the current ACDelco at most any parts outlet. The green stripe plugs seem common on ebay, the stripes are around the insulator.

 

Hope this helps

 

 

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The green stripes are older plugs.  The green stripes which were called "fire ring" plugs.

 

The green stripes were discontinued because if there was any variation in the rib the green would not print correctly and show a void.  To eliminate the appearance variation the green stripe was discontinued. 

 

No difference between green stripe and no stripe as long as the number on the plug is the same.

 

The most important thing when installing spark plugs is to USE A TORQUE WRENCH

 

If you tighten the spark plug over specified torque you will have the plug running colder than designed and possibly have a plug that would foul.  Not tight enough the plug would run hotter and you could either have the tip of the plug burn off and / or burn a hole in the top of an aluminum piston or other damage.

 

I worked for AC for a number of years including building millions of plugs while I was going to school.

Edited by Larry Schramm (see edit history)
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I went and bought another champion rj12c , which directly cross referenced to an ac46

 

when I asked him to bring out an ac R46 and compared it to the champion  rj12c 

 

the electrode was much higher almost 3 x which means it would go in deeper into the cylinder

 

so rather then get an unknown I stuck with the champions that were already in the car

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2 hours ago, Terry Wiegand said:

Larry, where does one find the torque values for seating the plugs?  I don't believe that I have ever seen anything to that end contained in the plug box when installing new plugs.

 

Terry 

 

Look in the service manual.  The spec is usually there. 

 

If not, a quick google search of spark plug torque will find a lot of charts for different size plug with and without a gasket(tapered seat).

 

You can look here.  https://www.google.com/search?biw=1280&bih=623&tbm=isch&sa=1&q=spark+plug+torque+chart&oq=spark+plug+torque+chart&gs_l=psy-ab.12..0i24k1.308795.308795.0.311103.1.1.0.0.0.0.141.141.0j1.1.0....0...1.1.64.psy-ab..0.1.140.kegHY5AGSno

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I am not sure about the cross, my AC book shows RJ12C crossing to C49. C49 would be beyond the heat range recommended by the manufacturer. What exactly on the plug is 3X times longer?

 

Hot plugs, like a 49, have been know to melt holes in pistons.

 

I have more books and will check further but I would use what the manufacturer recommended.

 

Dave 

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2 hours ago, Dave39MD said:

I am not sure about the cross, my AC book shows RJ12C crossing to C49. C49 would be beyond the heat range recommended by the manufacturer. What exactly on the plug is 3X times longer?

 

Hot plugs, like a 49, have been know to melt holes in pistons.

 

I have more books and will check further but I would use what the manufacturer recommended.

 

Dave 

 

A C49 spark plug would be a very hot spark plug.  The C would indicate that it was made for a commercial application like maybe a generator or route delivery truck.

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I defiantly do not want to use something bad for the engine

 

but all the cross references I have checked say a champion rj12c (also called a champion 592 ) is the correct replacement for the ac 46

 

the ac R46 is not even on the cross reference for the ac 46

 

and I compared the electrode tip of the ac r45 that produces the spark as much taller (goes in deeper) than the champion  rj12 c which looks physically identical to the ac 46

 

 

let me ask this to everyone please post replies

 

anyone else using a champion rj12c ( or champion 592) , how long have you been using them and how well do they work

 

 

anyone using an ac R46 (not the ac46)  , how long have you been using them and how well do they work

 

 

 

 

 

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You have heard a number of experienced Buick drivers give you their advice.

 

The plugs suggested by one of the major old Buick parts suppliers is:  http://bobsautomobilia.com/electrical/spark-plug-1938-1942-1950-53-.-ac-r45/ 

 

I have used them for a while in my 1937 Century with excellent results. I trust their recommendation.

 

The Chassis Parts Manual shows 46 as the original plug number for your 1940 Buick.   Pete Phillips, a respected Buick expert and editor of the BCA magazine, has offered to sell you a set of AC R46 plugs even cheaper than Bob's sells the AC R45s. You have two excellent economical choices to choose from there.  The "R" on a plug means it is a resistor style plug. When the car was new, I don't think they had figued out how to manufacture a resistor plug, but your car will be fine with resistor or non-resistor style plugs. With non-resister style plugs, you will have more of a chance of unwanted ignition noise interfering with radio listening or perhaps cell phone use in or near the vehicle.

 

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No, that is not what we have been saying. The currently available AC spark plug is R45 and is available at Bob's and many of your local parts sources. R46 will have to be sourced from members as offered above or ebay type sources.

 

R46 is a good plug, just not as easy to acquire as R45.  

 

Dave

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ok , I just want to use what everyone else is using

 

I can not get an AC 46 locally as it is discontinued

 

but I can get an AC R46 from someone I know locally

 

 

 

if everyone is using an AC R45 perhaps I should get that instead

 

I only want to buy a plug that everyone else is using and has been for years

 

so I know it has a track record of being safe for the straight 8 motor

 

 

 

 

 

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2 hours ago, buick special said:

ok , I just want to use what everyone else is using

 

I can not get an AC 46 locally as it is discontinued

 

but I can get an AC R46 from someone I know locally

 

 

 

if everyone is using an AC R45 perhaps I should get that instead

 

I only want to buy a plug that everyone else is using and has been for years

 

so I know it has a track record of being safe for the straight 8 motor

 

 

 

 

 

 

The item to be concerned with when choosing a spark plug is the HEAT RANGE which in this case is a 45 or 46. 

 

If it has nothing,  a C, or an R in front of it will have not affect on the performance of the sparkplug.  It could also be a LM45 and it will perform the same.  The LM plug is designated for a lawn mower and usually will have a screw top to connect the wire to.  Just a different top.

 

An AC 45 will give you the same performance as a R45. Period.  

 

That is as long as you TORQUE the spark plug to the specified torque specifications.

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If there was a problem with newer plugs being too long to fit under the cover would an LM plug not be the one to use.  I seems to me that they are shorter.  Personally, from my experience,  I would never use and AC or Champion plug if I could get an NKG.

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6 hours ago, Tinindian said:

If there was a problem with newer plugs being too long to fit under the cover would an LM plug not be the one to use.  I seems to me that they are shorter.  Personally, from my experience,  I would never use and AC or Champion plug if I could get an NKG.

There is not an issue with the 45 or 46 being too long to fit. The AC R45 fits perfectly and the AC 46 was the original equipment used by Buick. 

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Ok, let me do some show and tell.

 

The first picture shows four different spark plugs that are heat ranges from 41 to 49 and have regular thread except the last one which is a R45S.  The S designates that the plug has a small "skirt" below the threads.  The threads do not immediately start at the bottom of the plug.   The only differences between the plugs is the heat range,  the connection at the top of the plug which is called the screw, and the color of the printing on the insulator.  The difference in the heat range in these examples would relate to the particular application.  The LM49 spark plug because it is a hotter plug would probably be used for a 2 cycle lawn mower that uses a gas/oil mixture and would have a tendency to foul out and the hotter plug would minimize that possibility.

20170805_074342_resized.jpg

 

The picture below is of a cut away of a sparkplug insulator and shell.  This insulator starting from the left has the tip.  This could be made from a special steel as in "traditional" sparkplugs or newer plugs have much smaller platinum tips for longer life. 

 

Moving to the right, the dark area is the resistor material that gives the plug the "R" designation.  If the plug is not a resistor plug, then a fine powder like steel is put into that space.  The non resistive material would have the same general color as the tip and screw.

 

The next thing that you see is the bottom of the "screw".  The "screw" will change configuration depending on the particular application. LM/SP, etc.

 

When the plug is assembled the insulators are in a tray vertically.  The tip is dropped into the insulator.  Next the powder charge is added.  It would be resistor or plain metal. This material is also the seal to keep combustion gases from leaking from the tip of the plug to the top of the insulator and leak past the screw at the bottom of the screw.

 

 Next the screw is added to the assembly. 

 

When the parts of the plug are first assembled the screw sticks up above the top of the insulator about 1/2 inch (10mm).  The whole assembly is then put into an oven where it is heated up RED HOT and glows. When the assembly get hot it is then put into a press and the screws are pressed down into the insulator so the bottom of the screw is sitting right on top of the insulator.  It is then sent to a cooler to cool down slowly.

 

NOTE: If you look carefully at the top center of the insulator you will see a small groove where the insulator meets the shell.  This is the designation used internally for the heat range of the particular insulator.  Different heat ranges have a different number of grooves or out ribs.

 

The insulator is now complete and ready for final assembly.

 

20170805_074523_resized.jpg

 

This particular plug is a heat range 45.  If it was a hotter plug the tapered end of the insulator would be thinner and if it was a colder plug that area around the tip would be thicker/fatter.  The thinner tip does not allow the heat at the tip of the plug to be drawn from the tip to the shell to the head as fast as a thicker insulator tip.  The thickness of the tip end determines the heat range of the spark plug.

 

If you need any more information, let me know.  I made millions of these while going to school.

Edited by Larry Schramm (see edit history)
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Close, according to AC Delco, the S is extended tip. That's what I observed years ago with R44S plugs vs R44 plugs.

 

The Corvair used FF suffix plugs, and when they becme unavailable, AC made F suffix, which also has the "starter' unthreaded area like the S in your picture.

Spark_Plug, AC chart.jpg

 

I like your description of how they are made.:)

Edited by Frank DuVal (see edit history)
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Frank,

 

If you look at your picture above, there is an area below the threaded part that does not have any threads.  This is what I am calling the skirt.  Plugs that do not have an "S" in the numbering do not have that unthreaded area.

 

Thanks on the description comment.

Edited by Larry Schramm (see edit history)
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I got a better picture of a 44S and attached it. I also attached a picture of R44F. They look to have the same starter missing threads to me. But, maybe the S unthreaded area is slightly longer.I would include a picture of a non suffix 44, but most everyone knows they have threads all the way to the end of the shell.

AC 44S.jpg

AC R44F.jpg

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8 hours ago, Frank DuVal said:

I got a better picture of a 44S and attached it. I also attached a picture of R44F. They look to have the same starter missing threads to me. But, maybe the S unthreaded area is slightly longer.I would include a picture of a non suffix 44, but most everyone knows they have threads all the way to the end of the shell.

 

 

Frank,

 

After this discussion I would hope that everyone knows that the S designated plug does not have thread all the way to the end.  :)

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And on the S suffix the Tip extends further out from the shell. The length from the gasket surface to the electrode is longer on the S plug. 

 

I just wanted to show that the F suffix is also unthreaded, just like the same place on the S suffix.

 

I also hope they also learned that the number is only heat range on AC plugs, and the suffix can be important.

 

But have we taught them that AC in AC Delco is the same Champion as in Champion plugs? Albert.  :lol:

 

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Albert Champion was brought over from France by Billy Durant to make spark plugs.  They shortened the company name from Albert Champion spark plugs to AC Spark Plugs.  

 

My understanding that there was an issue between Durant and Champion and Albert left AC and founded a new company called Champion spark plug company.

 

AC Delco is just a marketing name put together when GM was creating Delphi and the component company Delphi.  AC without the AC name became a non entity when Delphi tried to sell spark plugs and other components under the Delphi name.  No brand recognition in the aftermarket.

Edited by Larry Schramm (see edit history)
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Larry,

 

ACDelco was around long before Delphi. It started as United Motors Service Corp in 1916 and in the 1960's became United Delco. AC wanted to go their own way and did for a period of time then in 1974 AC and Delco merged their sales forces and warehousing. They celebrated their 100 year anniversary last year. 

 

I guess we are getting away from the op's question.

 

Dave

Edited by Dave39MD (see edit history)
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2 hours ago, Frank DuVal said:

And on the S suffix the Tip extends further out from the shell. The length from the gasket surface to the electrode is longer on the S plug. 

 

I just wanted to show that the F suffix is also unthreaded, just like the same place on the S suffix.

 

I also hope they also learned that the number is only heat range on AC plugs, and the suffix can be important.

 

But have we taught them that AC in AC Delco is the same Champion as in Champion plugs? Albert.  :lol:

 

 

 

Thank you all for the wonderful and informative posts

 

Frank , what you posted above may explain what I saw at the parts place

 

I asked the parts salesman to bring me out an AC R46 plug

 

when he put it on the table and opened the box

 

I saw immediately that the metal that bends over the electrode came out further

 

Then the champion rj12C that I brought with me for comparison when they were side by side

 

That got me worried which is why I kept the champion and had started the original post

 

now when thinking back to that day I recall moving the AC box and believe it had several letters after the R46

 

and believe one may have been an S so I am thinking now he did not bring me the correct R46 plug

 

I will go back there In a few days to check on this

 

 

 

 

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