Resistor Spark Plugs

[capngrog]

I have been trying to trouble-shoot some ignition problems in an old 350 C.I. Chevy engine, and as part of the hoped-for cure, I changed the spark plugs, installing new Champion RV92YC resistor spark plugs.  Upon start up, I noticed considerable roughness in the engine operation and that the number 7 exhaust port was significantly cooler than the others (I measured this with one of those "whiz-bang" infra-red thermometers).  Some internet research revealed that resistor spark plugs should have a resistance of between 4,000 and 6,500 ohms, and a check of the old Accel 576s resistor plugs revealed a resistance range of from 6,500 Ohms to 8,300 Ohms, with most in the 7,000 Ohm range.  When I checked the resistance of the brand new Champion plug removed from the no.7 cylinder, I got a resistance reading of 60,000 Ohms.

 

During my research, I found that, a few years ago, there had been some problems with Champion spark plugs in General Aviation piston-engine aircraft which resulted in a re-design of their aero-engine spark plugs.  http://blog.aopa.org/opinionleaders/2015/03/19/champion-from-denial-to-acceptance/    It is my understanding that the producer of Champion aero-engine spark plugs, Champion Aerospace, LLC, is a separate entity from the manufacturer of Champion automotive spark plugs; however, I have not yet been able to confirm this.

 

With the foregoing in mind, I have a couple (or three) of questions:

1. Has any one else encountered a problem with excessive resistance in their automotive spark plugs, Champion or otherwise?
2. Is my information correct that we should be looking for a maximum of 4,000 to 6,500 Ohms resistance in a resistor spark plug?
3. Should I relegate my brand new Champion spark plug, with 60,000 Ohms resistance, to the dust bin?

 

I'd appreciate any input on this matter.

 

Cheers,

Grog

 

 

[Larry Schramm]

I would get all of the plugs in the same general range.  

 

If I was guessing (having made millions of AC resistor plugs) the Champion plug did not get a full load of resistor material when it was being put together before the heat & glaze operation. 

 

Try a new plug and if that is the only one, do a warranty return.  Just take a ohm meter with you to the parts store. 

 

If you want some pictures of the internal design of a spark plug, let me know and I can try to find my old samples and post the picture.

[Alfre]

Chevy does not like champion plugs in my business i have had meany chey and GMC gas engines and champion never lasted long, AC and others are better quality.

Al 

[cahartley]

^  I have had opposite results so........go figure....... 

[60FlatTop]

I'm a lifelong AC45 user in just about all the GM cars I owned. Maybe 8 years ago I got introduced to the NGK plugs through a 12 cylinder Jaguar I had. Since then I have been dropping my AC plug on the counter and matching the tips and reach to the NGK's. I'm pretty happy with them. Just that says a lot.

Bernie

[Robert Street]

Grog:

Back in the day I had a similar issue with a plug but don't recall the brand.  Just bought another plug and moved on as I recall because the car had been driven.

[5219]

I know that in recent years, all of the well known domestic plug brands have closed down their US factories and gone to Mexico. I also believe that the AC brand no longer belongs to GM. Has anybody noticed a decline in quality?

 

I buy NOS plugs for my antiques. They are easy to find and not expensive. I have had very little experience with newer plugs.

[60FlatTop]

I shifted to the NGK's after experiencing AC plugs that were unable to recover from an instance of flooding. They were recommended in the Kirby Palm Jaguar XJS living book, which is great reading even if you don't own a Jaguar: http://www.jag-lovers.org/xj-s/book/XJS_help.pdf.

They worked very well in a 1950 Super 263, a couple of Jags, and some other cars since I have been using them. I still have a stash of NOS AC45's and a big bag of sooty 44's. So it's either 20+ year old stock or the Japanese NGK's. For the rest of the ignition the only quality new parts I have found a Echlin at the NAPA store.

 

Just imagine the kind of person who would cuddle up with a printout of Kirby's book for an evening; I gotta get a life!

Bernie

[Grimy]

This is strictly anecdotal, but my experience has been that old NOS plugs with a "glaze" on the insulators surrounding the tip are longer-lived when used in less-efficient pre-war engines, especially side-valve engines.  The concept is that the "glaze" prevents absorption of unburned fuel.  I don't pretend to know the science, but I do know the results.

[capngrog]

I appreciate the responses to my thread, but I'm still curious about this situation.  I'll try re-phrasing my questions:

1. How much resistance should a resistor spark plug have?
2. Would it be a problem if a resistor spark plug had a resistance of more than 25,000 Ohms?
3. I have never before heard of this problem with excessive resistance in a spark plug.  Has anyone else ever heard of this problem?

Cheers,

Grog

[TerryB]

The resistance, from an electronics perspective, is not a major player when the source voltage is very high like what you get from a modern automobile ignition system.  I have never actually measured the plug resistance before installing them but it old be interesting to see what the accepted tolerance range might be for each manufacturer. 

 

Terry

[Larry Schramm]

8 hours ago, capngrog said:

I appreciate the responses to my thread, but I'm still curious about this situation.  I'll try re-phrasing my questions:

1. How much resistance should a resistor spark plug have?
2. Would it be a problem if a resistor spark plug had a resistance of more than 25,000 Ohms?
3. I have never before heard of this problem with excessive resistance in a spark plug.  Has anyone else ever heard of this problem?

Cheers,

Grog

 

Grog,

Go back and read my original post and your questions will be answered.

 

Here is a picture of a cut away spark plug which I made millions of.

 

If you look at the center of the spark plug, you will see the center electrode to the right.  Moving to the left you will see a dark area in the center of the spark plug and the upper electrode which is called the screw.   The dark area between the electrode and the screw is the resistor load.  If by chance there is an improper amount of resistor material (less than specification) then you would get a high resistance sparkplug. 

 

If you have seven plugs that are within 500-1000 ohms and one that is 6-10 higher, then you have a bad plug.

 

Take the high resistance plug back to the store and get a new one.