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I read that the "R" means it has a resistor. Is it ok to substitute say an RJ19LM into a machine running a J19LM?

Also, I'm wondering about the "s" at the end of the briggs plugs. For instance, 796112 vs 796112s. Can these be substituted for one another?

Thanks.

I've used J19LM and RJ19LM interchangeably over the years with no issues in my push mower.

Oh Boy,
A spark plug thread.
Almost as good as an oil thread .

All spark plugs have a resistance,
It is the air gap between the electrodes
That resistance depends upon the resistance provided by the air between them
So outside the engine it is a lot less than inside the engine and inside the engine it gets bigger as the compression increases .

Sparks happen when the potential energy ( we will call it voltage ) at the gap is bigger than the resistance of the gap .
However the voltage the gap sees , does not come down the wire at it's full level'
It starts at essentially 0 V and gets bigger till it reaches the maximum voltage that the coil can produce then drops back to 0 again .
Some where between the two 0 V levels we hope that it jumps the gap and ignites the fuel in the engine .

However there is a second path for the energy to escape and that is down the side of the center electrode and inside an engine this often is less than the gap .
When this happens we say the plug has gone bad and replace it .

The whole idea of a resistor plug is to prevent the voltage getting to the gap until it is big enough to jump the gap thus reducing the chance that it will leak down the side .
The upside of this is the internal resistance of the plug is often greater than the gap resistance so the accuracy of the gap distance is not as critical as it is with a standard plug

This is good & has been know from the very first day that a coil was used to fire an engine .

Remember that a wider plug gap RETARDS the spark which retards the timing and on a small engine there is no provision for adjustment other than changing the air gap between the magneto & the flywheel.
On a slow reving engine like a lawnmower this is not a big problem because the timing window for the spark is quite large and the power loss is minimal .
But on a high reving engine like a chain saw it makes a massive difference .

Now the big problem is not for the plug, it is for the coil and in modern engines the trigger chip for that coil .
The longer the voltage is building up inside that coil the more heat is being generated and heat is not good for the chip so can & does cause premature failure of the chip which kills the coil stone dead.
The other problem is higher voltages inside the coil increase the potential for internal shorting of the coil should there be any little flaws in the insulation of the wires.
On some engines it will make no difference at all on others it will kill the coil
Down here a plug retails for $ 7.50 and coils start at $ 45.00 so it is a no brainer to use the correct plug.

As cost pressures get greater and computer technology used in production get better coils will become more sensitive to the type & grade of plug because the wire maker for instance can use thinner wire & less laquer on the wire .

Woohoo a spark plug thread. Check the guns and knives at the door.
When the first engines had magneto ignitions solid core wires and standard plugs ruled the world. Then a guy named charles kettering invented the battery ignition system for cars. Solid core wires and standard plugs still worked then they started putting AM radios in cars. The ignition system became an audible tachometer in the radio from the EMI. So carbon core resistive wires and resistor plugs were introduced to stop the noise in the radios. Fast forward to to electronics sensitive to EMI. Carbon core or spiral wound wires and resistor plugs still reduce EMI. Older magnetos do not like resistor wires or plugs. Tends to raise the voltage needed to fire the plugs and it overheats the magneto. If you have an old magneto tractor use solid wires and non resistor plugs. Modern magnetos may or may not like resistor plugs. All depends on the magneto. MOST modern magnetos resistor or non-resistor won't make a difference SOME equipment will require resistor plugs to supress EMI.

lefty2cox said:

I read that the "R" means it has a resistor. Is it ok to substitute say an RJ19LM into a machine running a J19LM?

Also, I'm wondering about the "s" at the end of the briggs plugs. For instance, 796112 vs 796112s. Can these be substituted for one another?

Thanks.

Click to expand...

And the -s is just that they made a minor change hat has little to no consequence.
Could be nothing more than than , in a box , or on a blow moulded card or in a trade pack of 144 loose plugs .
Could be they changed the gap , or it is pre-gapped or not pre-gapped

Covid 19 must have folks locked down and not want to jump into a spark pkug thread.?

" my spark plugs are better than your spark plugs"?

Well...I feel like the prettiest girl at the dance. Thanks for the info. Very much appreciated as I've recently started studying electronics and this was super helpful. If I understood correctly, as far as the resistor vs non-resistor, it depends on the machine, resilience of the coil, as well as how critical timing is. Got it, I think.

Thank you for the "s" clarification as well. I'll stick with the standard plug for this machine then because I'm working on an older one. I do, however, have a correct cross-reference in my spark plug draw, it just has the "s". I'll gap it properly. I own this machine so any adverse consequences to my mistakes will be my own.

S means "Synthetic"!!

Maybe no knows actually reason why resistor spark plugs came existence. They are to reduce RFI and is now must many systems with computers and other electronic components. There is both resistor and inductor types with the same purpose of reducing RFI. RFI still affects analog radio communications including the automobile AM radio band. At one time cars passing your home would screw up your television reception too much like air capacitor arcing due to much RF voltage being applied for the air gap.

I use to drive my family crazy while on CW by flicking the touch control lamps thru all its modes. I finally found that problem was that I was using a receiving air cap instead of a transmitting cap. I could actually see the acring while keying.

How many people here do you think will know what "CW" means? I do.

If you were talking electrically, you have three choices, Construction Wireman, Carrier Wave or Caution/Warning. Problem is it should be abbreviated C/W. CW without the slash would mean Clockwise. At least that is how I taught my students.

Then there Continuous Wave or more commonly as Morse Code transmission and yes I still transmit in that mode as it becoming less common we relay things in code two ways.

A bit familiar with CW. I was a morse interceptor in the Army back in the 70's in Berlin. Nothing like sitting and hacking dits for 8 hours a day. Only thing that makes it better is having a massive hangover and a raging thunder storm for an entire shift. Sure as heck can't do it now but i used to do 22 WPM.

Hammermechanicman said:

A bit familiar with CW. I was a morse interceptor in the Army back in the 70's in Berlin. Nothing like sitting and hacking dits for 8 hours a day. Only thing that makes it better is having a massive hangover and a raging thunder storm for an entire shift. Sure as heck can't do it now but i used to do 22 WPM.

Click to expand...

Thank you for your service , Hammer ??????

lefty2cox said:

Well...I feel like the prettiest girl at the dance. Thanks for the info. Very much appreciated as I've recently started studying electronics and this was super helpful. If I understood correctly, as far as the resistor vs non-resistor, it depends on the machine, resilience of the coil, as well as how critical timing is. Got it, I think.

Thank you for the "s" clarification as well. I'll stick with the standard plug for this machine then because I'm working on an older one. I do, however, have a correct cross-reference in my spark plug draw, it just has the "s". I'll gap it properly. I own this machine so any adverse consequences to my mistakes will be my own.

Click to expand...

Usually spark plug threads bring out all of the You-tube watchers experts then the Ford / Chev brand prejudices etc & they can be a lot of fun .
Perhaps the scarcastic humour right from the start scarred them off .
Seems like you have your head screwed on right.
Plug grades & types are far more important for magneto ignitions than standard kettering ignition ( battery coil ) .
In almost the earliest motor cycle magazine I read was the brass button bodge for cleaning a fouled plug.
The Brass Buttons ( because every one wore old army great coats with brass buttons ) was to run the spark plug HT cable to a brass button then hold it off the spark plug .
This forced the spark to jump a fouled plug gap and eventually burn the crud off.
It is still a standard method of detecting an bad plug by a lot of mechanics & was one thing that those electronic tune up machines used to analyse your engine which were really popular in the 60's & 70's.
It is also what was behind all of those magic mileage / power boosters that were popular in the 70's & 80's till people realized they were a fraud.
I you can wrap your head around electronics then you are one in a million .
And once you have things sorted, buy your kids / grandkids / nephews & neices electronics kits to get them into it.
Nothing a small child loves more is to make a machine that makes a fart noise.
A bit off topic, but worth talking about
there are 3 things that every parent should give their kids to "play " with that will set them up for life
1) a musical instrument
2) a magnifing glass / microscope
3) electronics kits

I had a magnifying glass, set everything on fire that I could during a sunshiny day.

I thought the three things you let your kids play with were guns, knives and fireworks. It weeds out the dumb ones. ?

Hammermechanicman said:

I thought the three things you let your kids play with were guns, knives and fireworks. It weeds out the dumb ones. ?

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that trick didn't work on me, heaheaheaheahheaa