These have been running in my car for over a year. What are they telling me?
Normal burn. Mixture is correct. Doesn't seem to be burning oil. I know there is a dark oily/sooty area at the bottom outside of the plug but that is common and normal. If that area were white, it would indicate a lean mixture. The area inside the plug at the electrodes appears to be a light brown which is what it should be. If that area were white, lean mixture. If it were dark black or had a lot of build up then that would be an indication of rich mixture or burning oil. Have you done a compression test and if so, what did it show?
I have not done a comp test, but it has plenty as it is a bit of a chore to crank it over by hand. I was very pleased with the looks of these plugs. This is with the modified NH carb I had been running. Will be curious to compare at a future time after running with the "new" Stromber LF.
They look pretty good as far as running. Good color where it counts. I see two that MAY indicate a problem.
#4 is running in some oil. Check the compression. if it's lower than the rest, could be rings. If not, intake guide may be over wear limit.
#3 looks like it could have antifreeze/water exposure. Could be the head gasket or a crack in one of the valve seats. It's still firing so the leak may be minor.
Probably has a rough idle but runs good on the road. Most owners would ignore the signs and keep going.
My eye might be a little out of calibration, but the gap on #4 looks a little too narrow.
I concur the burn patterns appears very satisfactory.
All in all, they seem to be operating fine for a set of old worn out spark plugs. Being the nice guy that I am I'll trade you those old worn out spark plugs for a set of shiny new A-25s.
: ^ )
I must say, the images look more intense than the plugs in real life. #4 looks more oily in the photo, #3 has antisieze on it, no rust. Valve guides are fresh, excellent smooth idle.
Keith, you are toooooo kind.
Here is a comparison from before I did the valves. #1 is on the right again.