Spark plug and cross referencing talk

General Discussion
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[TLDR: In small engine applications, will a resistor plug cause problems if a non-resistor plug is spec’d? Anyone know anything of “Torch” brand spark plugs? Any suggestions for a known reliable spark plug crossref website?]

Don’t tell anyone that this post originates in finding a suitable plug for my generator…

But to start with cars, I always just buy original OEM brand & part number, and don’t think twice. I’ve always done the same with small engines, which have normally come with NGK or champion plugs. I’ve never had any spark plug problems, and have always just replaced them on a maintenance basis before I’ve had any problems.

But my generator - which recently gave me starting problems when the darned power went out at 7:30AM w/ the temps at 8F (!) - is a Westinghouse that comes out of China with a Chinese Torch plug (F7TC).

Although I didn’t have any trouble with that plug, I’ve heard not-so-great things about Torch plugs (besides that I can’t get them locally). So when I changed it I think I just asked for a crossref at an auto parts store. I ended up with an Autolite 63. It seemed ok for a while (I can’t tell you how many hours are on it, but it’s no where near hours to change it).

As I was struggling to get the generator running, it became apparent that it was getting flooded. I still had the Torch plug, so I threw that back in and that seems to have been the issue. (One pull, and blew smoke for a bit). And none of this was b/c the gen had been sitting a long time. I start it up about once every two weeks to a month, and had run it for several hours a couple of days prior.

So, I did a little searching, and found many with Torch plugs having switched to NGK (mostly reports of BP7ES), with very good results (easier starting/smoother running). So I went to a big box AP store (Saturday, so my little local place was closed). I was first sold NGK BPR6ES. Checking up on that using the web, the 6 is fine, I think. Just a little hotter than the 7. But, I’m pretty sure that the “R” is NOT fine - resistor plug. The F7TC is a non-resistor. (Torch also uses an “R” in their number if it’s a resistor). I’ve since learned that the Autolite 63 is a resistor plug. So, maybe that was its problem?

Ok - so back to the AP store. Every last thing that they cross reference is a resistor plug. They don’t even sell any NGKs at all that are non-resistor - or if they do, none come up under crossref. Went on to looking at what they had in Champion (my manual does give me a N9YC). And once again, everything was a resistor plug. (I tried both an Advance and O’Reilleys)

(I later just went to buy NGK BP7ES online and the only place I could find them was in Europe. WTH?)

Anyway…I guess so far I’m just telling a story. I get what a resistor plug does, but this is not a car so it doesn’t need one - and probably isn’t supposed to have one. Without the resistor, I should have stronger spark, yes? Or am I barking up the wrong tree?

And does anyone have opinions about the Torch plugs? Maybe I’m wrong to brush those off too.

And how can the crossref data bases be so weird? First, there are the ones at the AP stores, but I also get all sorts of weird things on my own internet searches (usually landing here: Torch F7TC - Alternative spark plugs). There are a few weird things going on in there, but I won’t bore you with the details unless someone wants to know. (And yes, I see the note at the top says: “The cross references are for general reference only, please check for correct specifications and measurements for your application.”)

Anyway…there are reasons I’ve always just bought whatever came installed by OEM!

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Here is what Napa’s commercial website shows for a cross reference…

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Here is the specs for the NGK 5534 (BP7ES)

Attributes
Brand: NGK
Contents: Nickel tipped spark plug w/gasket
Electrode Core Material: Copper
Gap Size: .032 in
Ground Electrode Quantity: 1
Hex Size: 13/16 in
Insulator Material: Ceramic
Insulator Type: Projected
Manufacturer: NGK Spark Plug
Manufacturer Part Number: BPR7ES
Resistor Type: Yes
SDS Required: No
Seat Type: Flat
Spark Plug Heat Range: NGK7
Spark Plug Hex Size: 13/16 in.
Spark plug Inductive: No
Spark Plug Reach: 0.750 in
Spark Plug Resistor: Yes
Spark Plug Resistor Value: 5000
Spark Plug Seat Type: Gasket
Spark Plug Thread Size: 14 mm
Sub Brand: Standard
Terminal Type: Removable Nut
Thread Size: M14-1.25
UNSPSC: 26101732
VMRS Code: 033003005
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I have mostly all Briggs small engines so I tend to use Briggs oem when they are available or champion. I always used ngk in my toro Suzuki engine. The only thing about champion is that Taryl said they have had problems with the gold topped champions not the silver. I’ve got both in my drawer that maybe I’ll use sometime. I trust ngk and for the five bucks or so would be what I would use. I’ve never used auto lite but ac in the Gm cars, per the mechanic I had in 1968.

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Thanks Dave. That NGK is a resistor plug. A quick search tells me the Champion is too. Based on how things have been so far, I’d bet that the rest are as well. Anyway, my little local AP store is also good with small engine stuff. I think I’ll visit them on Monday.

Ya, I’ve always been partial to NGK or Champion in small engines. I might just order up some of the Champion N9YC’s online and see how it goes.

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The resistor changes the slew rate of the ignition pulse. It’s not going to stop the plug from firing but will delay the arc timing. So if your engine has a very basic ignition system and is sensitive to ignition timing, the resistor plug may have some noticeable impact.

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Thank you.

NGK also tells me that "Since resistor type plugs actually ““resist” some of the spark energy, non-resistor type plugs actually deliver a more powerful spark.”

But perhaps it’s not normally enough to matter, or the most important thing? Although it does say they’re preferred in cars for racing.

In any case…I’m just going to leave the resistor as a maybe/maybe not a problem, but just make sure to always use non-resistor types in the generator.

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Well, there’s a lot behind the scenes so to speak. The coil is going to continue to build voltage until there is a breakdown (hopefully at the spark plug gap :slight_smile: ). The resistance in the plug is minimal compared to the resistance of the gap. As mentioned, the resistor slows the rate of output voltage building (slew rate) and when we talk about the physics of the cylinder pressure and gases within, a fast rise time typically leads to an earlier breakdown and lower ignition voltage. So in some respects, the presence of the resistor in many cases will contribute to higher discharge energy than one without. It’s not as simple as ohms law as many would think.

However, if it does have some minimal reduction in spark energy under particular conditions, I would argue that it is inconsequential in most situations. Yes, in a racing situation where every bit of advantage is worthwhile, then it makes sense to maximize everything you can. Plus they are not worried about EMI.

In most other applications, it isn’t often a limitation. This is especially true for complex, electronic ignition systems that can control most aspects of the ignition cycle. So like I mentioned, for very basic ignition systems and engines with less flexibility to withstand temporal changes in timing, the resistor might have an adverse effect. When in doubt, default to the recommended part always.

Company I work for designs and builds all kinds of high voltage discharge energy devices; both triggered and non-triggered. Used in all kinds of applications from power distribution networks to the Titan missiles aboard our nuclear subs. Some use series resistance to alter the Q of the ignition circuit. Just in case you were curious if what I said was accurate or not…

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Oh - not at all curious about whether or not what you said was accurate or not. I’m sure it is. Not questioning it, and I appreciate your time. One of the reasons I asked here is because I know that there are quite a few people here with serious technical knowledge, and I absolutely count you among them. I guess I was just probing for some commentary on the higher resistance.

I think that if I could ask again, it would be “is this NOT as simple as Ohms law?” (You answer is obviously NO!) In your first reply you only mentioned slew rate. I get that in a generic “I’m not an engineer” sort of way. You just didn’t mention the resistance issue - perhaps because it’s not the most relevant thing.

Anyway, going by the common-sense ohms law thinking, I looked up the NGK specs on the BPR7ES (resistor plug) and the BP7ES (non-resistor plug). The “R” version is 5K ohms. The non-R version is 1K ohms. To me that seems like a lot. (Esp in challenging conditions - a small engine at 8F).

But I guess not, or only maybe. It still doesn’t matter at this point. I won’t put a resistor plug in this generator. But I appreciate the time people have taken to respond.

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Apparently, Torch is an established brand although not well known in the states. I found you can buy a package of 4 of them on Amazon for $11.99 and delivered by Friday this week if you have Prime. The low price normally scares me but in your case, since you had poor performance with the resistor version of an alternate and non-resistor plug are less common, I would spring for these exact replacements. Even if they don’t last long, you have 3 replacements ready to go :slight_smile:

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Again, many thanks.

Obviously online gossip is always questionable, but in addition to reports of early electrical failure of Torch’s, there are also reports of dislodged electrodes. I have not spent a lot of time to verify that they are truly an issue, or if this is just a matter of being able to find anything you like in online gossip. (Tho’ there are plenty of threads about them on Bob is the oil guy, and discussions there don’t tend to be worthless).

But I just ordered up a 4-pack of the Champion N9YCs for $16 and should have them tomorrow. I’m sure I can get something suitable from my local AP store as well, but just haven’t had time to go there.

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lol …+1 … good point :slight_smile:

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All I can say about the Champion so far is that the thing start and runs. It will take a while to see how things go. At least it’s a brand I know and have trusted.

In defense of the “Torch” - which is actually labeled “LG” on the plug (I think it’s the same manufacturer and the # is F7TC) - it had quite a bit over 100 hours on it (change interval is 300) and was doing fine. Very little electrode wear and still well within gap spec (.028 - spec is .027-.032). Meanwhile the Autolite 63 with many fewer hours on it also had little to no wear, but was all sooty. I think it’s just a bad match for this ignition system - whether due to the resistor, or maybe the heat range - even tho’ it does some up on crossref. Apparently heat range #'s aren’t standardized across manufacturers, so I have no way to compare.

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I’m pretty sure that some of my small engine plugs are resister, maybe all. I just thought it had more to do with radio interference.

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As far as I know it does. (But as per @TwinTurbo above also changes the slew rate of the ignition pulse so could be an issue in simple ignition systems). The radio interference apparently can also interfere with the other electrical signals including the on-board computers (or so NGK tells me). So all cars these days will use resistor plugs. But most small engines shouldn’t need them, although I guess that might depend on the ignition system (?).

Anyway, IDK. This is literally all new to me. Never looked into as I’ve literally never had any trouble with spark plugs before. And when I was sold resistor plugs at the AP stores for my generator, but found non-resistor plugs in my manual, I wondered…and went down a rabbit hole…

But I’m learning. Over all of the years that I’ve been here, that’s often been the point. I like to learn things. It’s empowering.

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I find this type of discussion fascinating and enlightening and the primary reason I have liked to frequent this site over the years. Engaged with others in meaningful discussion…

Look at the difference between the electrode stick out on those two plugs. It is pretty significant. I’m betting the heat range difference was a big factor in this application.

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Agreed!

Once I was able to put the two plugs next to each other I was thinking heat range as well, but I don’t know enough the say. (And hadn’t noticed that electrode difference until you mentioned it). The N9YC’s I just put in are on the relatively “cool” end of the plugs that crossref to the originals. I plan to watch them, and if I see signs of soot, I figure I’ll go to a hotter plug, like the N7’s. Or find the NGKs in the 5-7 range.

The heat range is also something I’m in the process of learning about…

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I wonder if resistor plugs might be less susceptible to small engine ignition system designs , and their electric glitches, which would otherwise cause misfires?