Sparkplug Equivalents

[RES]

From my research it appears that the Bosch #WSR6F mini-plug is equivalent to the NGK # BPMR7A for use on Stihl saws. Am I correct? Any advantage to using the NGKs?

 

[sedanman]

Interchange is correct. Run either no noticeable difference.

 

[Reddog]

Same, I have run both and not seen any diffrence.

 

[ray benson]

Pretty in depth small engine sparkplug cross reference chart on mike's site.
http://64.180.101.188/cscc.nsf/673d...e39d1995d7ddc91588256e0c00029d0f?OpenDocument

 

[Allan.K]

Hello..I sell NGK plugs for small engines..I have really good luck with them over the years.. And ppl seem to really like them alot to..I run them on everything I own and sell for small engines.. If it comes in with out a NGK or Bosch it gets a NGK ...Yes the BPMR7A is the right plug for it.. But I never stock any plugs with a resistor built in them..Thats what the r stands for in the lettering..So I install on a stihl is a BPM7A Stock number 7321...In fact most of the stihl saws run that same plug the only ones that don't are 042av,07,070,08s,09,090,1601 and a 1108-contra...Matter in fact most husky's use that same plug too ..I carrry one plug hotter to the BPM7A it is a BPM6A...Like I said I have alot of ppl very happy with the NGK plugs...Even alot of commercial guys use my NGK's and they swear by them ...I never stock or use a champion,AC or Autolites tho..

Here something funny I have a guy running NGKs in his harley and he swears by them now ....

If anyone needs any help finding a NGK plug for there saw let me know ..
Allan

 

[sedanman]

Allan, What is your 'logic' in not stocking resistor plugs? How is is that you figured out something the engineers missed? Just because a non resistor plug 'works' doesn't make it right. Can you tell me what effect the resistor has on the spark?

 

[TimberPig]

Allan, What is your 'logic' in not stocking resistor plugs? How is is that you figured out something the engineers missed? Just because a non resistor plug 'works' doesn't make it right. Can you tell me what effect the resistor has on the spark?

The resistor is there to cut down on radio interference. If the ignition system is getting weak, it can reduce the spark slightly, possibly enough to cause it to not run. The correct repair procedure in that case, is to fix the ignition problem, not just mask it with a non-resistor plug.

 

[Jim Mesthene]

A quick look on an occiliscope will demonstrate that a resistor plug fires at a higher voltage (more resistance to overcome). Higher voltages can leak through wires or dirt but they also fire better on a dirty or oily plug. The plug will last longer at higher voltages. Capacitors in the ignition system may be matched with resistor plugs.
I'd go with the designer's choice unless I could show, on a 'scope, why my idea worked better.

 

[Allan.K]

The resistor holds back a percentage of your ignition power.. It is not as hot or as true of spark as it could be. ...And every repair shop that works on two-cycles around here for many miles don't carry the resistor plugs at all not even the sled shops or motorcycle shops that sell or fix 2 cycles..They feel the same way about it..It holds back the ture fire power of your ignition.


TimberPig....And no I don't put them in to mask the problem either thats for a someone that wants to make a fast buck off someone and don't give a cr@p about there customers...I never take any short cuts..Thats down right dirty and WRONG to treat ppl that way....
Allan

 

[TimberPig]

The resistor holds back a percentage of your ignition power.. It is not as hot or as true of spark as it could be. ...And every repair shop that works on two-cycles around here for many miles don't carry the resistor plugs at all not even the sled shops or motorcycle shops that sell or fix 2 cycles..They feel the same way about it..It holds back the ture fire power of your ignition.


TimberPig....And no I don't put them in to mask the problem either thats for a someone that wants to make a fast buck off someone and don't give a cr@p about there customers...I never take any short cuts..Thats down right dirty and WRONG to treat ppl that way....
Allan

Nowhere did I say you did. All I said was that a resistor plug would sometimes hold back the spark enough, on a failing ignition system, that it wouldn't run, and swapping to a non-resistor plug would sometimes let it run. Then I said that repairing the failing ignition was the proper repair, not swapping the plug. I never said anything about you doing it to cheat customers or anything of the sort.

I've run both resistor and non-resistor plugs in enough 2 stroke engines to never notice any difference if the ignition is sound. Your theory on using resistor plugs to provide the "hotter truer spark by not holding it back" is long on believeing it is true, but do you have anything to actually back it up? The fact that sled and motorcycle shops don't use them isn't exactly proof by scientific method, it is simply a belief held by a bunch of people. In order to prove it, you'd have to actually design and conduct a scientific test to prove that non-resistor plugs were actually providing a superior spark and thus superior running. Since you haven't done this, all you have is unsubstantiated beliefs. There is also that fact, that in some digital ignition systems, the radio interference caused by running a non-resistor plug can actually cause misfiring of the ignition system of the motor it is being run in.

 

[Allan.K]

Nowhere did I say you did. All I said was that a resistor plug would sometimes hold back the spark enough, on a failing ignition system, that it wouldn't run, and swapping to a non-resistor plug would sometimes let it run. Then I said that repairing the failing ignition was the proper repair, not swapping the plug. I never said anything about you doing it to cheat customers or anything of the sort.

I've run both resistor and non-resistor plugs in enough 2 stroke engines to never notice any difference if the ignition is sound. Your theory on using resistor plugs to provide the "hotter truer spark by not holding it back" is long on believeing it is true, but do you have anything to actually back it up? The fact that sled and motorcycle shops don't use them isn't exactly proof by scientific method, it is simply a belief held by a bunch of people. In order to prove it, you'd have to actually design and conduct a scientific test to prove that non-resistor plugs were actually providing a superior spark and thus superior running. Since you haven't done this, all you have is unsubstantiated beliefs. There is also that fact, that in some digital ignition systems, the radio interference caused by running a non-resistor plug can actually cause misfiring of the ignition system of the motor it is being run in.

Sorry about misunderstand you about ...How I run my shop....:bang:

But I will tell you this ..I been working on engines for many many years snice the mid 70's.From tractors to model airplane engines.....I had a Polaris Indy 650 with aaen engine that would suck more fuel then ever thought of.. I draged it up in Mn at hayday's..years ago..That sled did not like resistor plugs..It ran better with non-resistor I don't why but it did.. And you know how told me to run non-resistor plugs Aaen did so did SLP pipes and they both said it and I heard from many others too .. That a non resistor has a hotter spark..But that has been years ago..I know things have changes alot over the years and I changed with the years just have old school and new school knowledge ..I just like non-resistor plugs thats all.. I do have resistor plugs too.. Becouse not all saws I can get non resistor plugs..I am not trying to start a p!ssing match here..ok...

 

[TimberPig]

I wasn't either. The case of your modded 650 is a specific case, where it did make a difference, but for normal stock engines, the difference isn't likely to be noticeable.

I'll admit I run non-resistors in some stuff, and resistors in others. I have no real preference so long as it makes my engine run and it's performing as expected, it makes little difference to me. The resistor plugs are slightly more expensive, so non-resistors are more attractive for dialing the jetting on a bike or sled that is fouling them out quickly. I believe in Canada we are actually legally required to use resistor plugs in cars and such, but I've never heard of any sort of enforcement, so I don't bother worrying about it.

Interesting fact on NGK, they don't make a plug that is the exact correct plug for the Polaris Liberty twins. The head was designed around the Champion plug that comes in them stock, many have and do use the closest cross that NGK has successfully, but lots have tried it and been dissatisfied. I like NGK plugs too, but I've had good results out of Champions and Bosch as well. I've been fortunate not have experienced the problems other have with Champions falling apart. So long as my engine is running well, and the plug isn't fouling, I don't worry about what the name on the plug is.

 

[Allan.K]

Here some food for thought...On non resistor vs resistor.. right from a high performce site about spark plugs

So non-resistor spark plugs are better for performance?

Yes. If you are looking for performance you want to use non-resistor spark plugs. A resistor is exactly what the word implies. When the spark crosses the point of resistance some of the spark energy is lost. A resistor is like an electronic obstacle and could be the cause for a weak spark. Non-resistor spark plugs deliver a more powerful spark.

I thought I would bring out my point why I like them so much....

 

[Allan.K]

On Stock engines I do doubt it will help out much on them..But I just like givin it any little help I can...

 

[cuttinscott]

actually resistor plugs are recommended for many chain saws and cutoff saws so not to interfere with elec. governed coils.

Scott

 

[ray benson]

I was told by a Makita service center head mechanic that the makita cutoff saws use a resistor plug. Using a non- resistor plug burns up the electronic ignition. He showed me 7 saws from a large contractor that all had bad ignitions. All caused by the well intentioned contractors mechanic putting in non-resistor plugs. He said if it calls for a resistor plug then use only a resistor plug.

 

[Freakingstang]

I never really took too much thought to the resistor plugs and the ignition....

My Husky dealer a long time ago once told me when I asked the difference between a resistor and non resistor in a chain saw...

"Does your Chainsaw have a radio" was his answer. I thought about it and chuckled. Nave been using non resistor plugs for years withou any problems, although none of the saws I run have a rev limited coil....

 

[Allan.K]

I asked that question to a few Stihl dealers and a few Husky service shops and they all use non resistor plugs with no problems..And they all service tree service company's plus others.But never know about them other name brands either....Kinda like cuttinscott said it could be becouse of them so called governed coils now day's.. I think I am going to check into that with a my stihl dealer and see what he say's ....What's next to screw up saws besides epa..:bang:

 

[RES]

So the question remains is it better to use a resistor plug that fires with a higher voltage or a non-resistor plug that delivers more energy since there is no resistor to steal energy away?

 

[Allan.K]

So the question remains is it better to use a resistor plug that fires with a higher voltage or a non-resistor plug that delivers more energy since there is no resistor to steal energy away?

I would say that is up to you..

Like I said before I use non-resistor ones...But each there own..With rev limit coil's I could see a problem...But I bet your a@@ I will try one out on one and see if it is true ...lol.. But that is just me.