julien_d said:
Given one particular engine set up as the standard, you have plug A and plug B. Plug B has a higher operating temperature in our current engine setup than does plug A. So naturally plug B introduces heat into the engine that plug A does not.
Nope. Plug B just transfers the available heat from the plug nose to the steel plug body more slowly. Same heat energy in the engine, same heat introduced to the plug nose, but just a less efficient cooling path to the available heat sinks the steel plug body and the cylinder head.
If you were to remove the steel plug washer install a thin fiber washer in it's place you'd see the plug act like it was a hotter plug. No change in energy, just a less efficient path for the heat to travel along.
Thermodynamics aside, the moral of the story is:
- plugs need to be hot enough to keep the nose fairly clean
- load, and time under load have the biggest influence on plug heat range required
- If your riding stays the same, and your bike is jetted correctly, the weather has no influence on the plug heat range required.
If you pull plugs once in a while you'll see they will give you a very clear indication of whether or not they are running at the right temps.
Evidence of a grainy insulator or a glazed look points to an excess of heat. The ceramic will look like a glazed donut with a weird shine if it's running too hot. If it's on the edge of being too hot you'll see small spots where the glazing is just starting to appear, usually close to the center electrode.
If the insulator surface looks similar to a new plug with just a very slight coloring (two-strokes only) then it's running at a safe temperature.
If it's too cold you'll see too much color and a build up of deposits on the ceramic.
sr5bidder said:
hey thanks Rich I found your post from 1999 that you have just copied and pasted, but have also read something from Gordon Jennings: "there's a 125cc motocross machine residing in our shop which runs a lot stronger and cleaner since it has been retimed for less advance, jetted leaner, and been given a hotter spark plug."
you say if it doesn't foul forget about it while in the same artical Gordon speaks of fuel film on the eletrode and the insulator tip being hot enough not to allow any soot build up..
I have preached about running plugs hot enough to keep the insulator clean for ages. You have to keep in mind that most people are convinced they should see a plug color that looks very dark (too cold with too many deposits) so trying to convince them to do otherwise scares some people. No one ever broke an engine because they ran too cold a plug, but they sure have hell have slowed a few down. ;)
Long ago, Dr. Theodore VonKarman wrote:
"When you are talking to technically illiterate people you must resort to the plausible falsehood instead of the difficult truth."
The sad fact is, lots of riders don't want to understand or don't want to be bothered, so the advice to not mess with it if the plugs don't foul is a safe approach for them.
Gordon Jenning's took some flack over the years for his views on plugs but in my opinion he was dead on accurate. I think he took the correct approach by explaining things in detail and trusting people to be sharp enough to do the right thing with the information rather than just glossing over things with a "plausible falsehood" like most magazine guys do.
I try to do the same as GJ when I can. I'm convinced the more riders know the better the chance of them making good decisions and having more fun along the way as a result.
As you get deeper into the specifics of tuning you'll find that the chocolate colored plugs that so many strive for are a just safety crutch for disinterested (or technically ignorant) tuners. They are a long way from a proper setup.