Spark plug number query?

[Enigma]

I had a very rough running engine and did all the usuals maintenance items and finally found that I had a dead plug. I found a set of RN 12 YC used plugs that cured the problem. I have a 7:1 engine which originally had N8 plugs. I know that the numbers mean their heat range but what I don't know is the different effects that the different ranges do.
Terri Ann suggests RN 11 YC and I just bought a set. I also saw some Rc 9 YC. Should I exchange them or is it ok to run the 11 YC"s

Thanks John

[cousindave]

I love the yc's

[Enigma]

But what do the numbers mean for the engine. Does one run hot plugs or cold plugs and which # is which and why??

[Donnie]

But what do the numbers mean for the engine. Does one run hot plugs or cold plugs and which # is which and why??

Hi, The R =resistor, that is a a carbon impregnated string in place of a stranded wire core, A wire of the older style will carry the spark, but will cause RFI or radio static, tv shudder and a whole host of other undesirable effects, mostly unknown to you unless you have a radio in your rig. Your neighbors will know................:-0
the #'s 5 8 9 10 etc in the range in which the plug heats up to to burn off undesirable deposits..the lower the #= the colder the plug burns, thus it will allow carbon to build up on the tip & foul the plug..== a high compression engine will require a colder plug because the heat in the combustion chamber is much hotter and a hot plug {hi #} will quickly burn off the tip ,or ping on acceleration,,, A lower comp engine, yours, or a worn engine needs a hotter plug to ward of the build up of carbon, from oel consumption, and other factors such as the octane rating of fuel, methanol & other gasoline additives.
C is the "wire core" running down thru the plug...C= copper .Most plugs went to copper years ago under the thought process that copper was a better mousetrap...newer plugs have gone to platinum, silver & a host of other metals, none to be considered for your use.....I just got up so I hope this all makes sense...Oh, yes B4 I forget, a simple test is to drive your rig under the normal conditions that you usually drive, myself , my 109 is used only on highway driving to swap meets, so after a half hour of driving, push in the clutch , shut off the engine, coast into a rest area, allow the engine to cool, then remove 1 plus & read it. it should be a grey color..not white=too hot. not black=too cold or other problems, not always plug related...another tip, when changing plugs remove them & keep them in order from front 2 back, this will allow U 2 find any problems. cap, wire, cyl comp, wrong plugs etc. good luck, Donnie

[gudjeon]

I cross referred to an AC R44XL. Cross over directly from the old skool design of Champion N8. 10 bucks for 4 fit my bill perfectly. Projected electrode to put spark more in the centre of the combustion chamber. I use these on my 7:1 engine and works a charm.

[yorker]

RN12YC
R= resistor
N=14mm Thread
12=Temp Range
Y= extended nose
C= copper