Bonneville America Forums Forums Technical Forums General Tech Spark plug question

I pull my plugs every couple of months to see if they look ok. The last two times I noticed something unusual. If you hold the plug bottom up with the side electrode away from you, one half to the left is a different color than the half to the right. This is exactly the same on both plugs. They are tan on one half and off white on the other. If you averaged the two colors it would be near perfect. The measured gap is set at .85mm and everything else looks fine.

Can one of you more serious wrenchers explain why both plugs have this split appearance?

Are you using stock NGK plugs, or NGK iridiums? Have you side-gapped your plugs?

Below was copied from this website.

The Spark plug to the left is what a normal plug should look like. Grayish-tan to white in color indicates the plug is operating at the proper heat range as well as correct jetting and the cylinder is running healthy. RACER TIP: That vertical color band on the ceramic shows you where the plug is indexed. Meaning that band is aimed slightly at the exhaust valve. Optimum location places the band HERE. If the band is anywhere but here, it means that when the plug is not at it's optimum location. There is still discussion as to whether indexing a plug is worthwhile, but on may applications looking for that last horsepower, it doesn't hurt.

Hope that helps. Sounds to me like they're okay. If you want to check it out, take a black Sharpie and mark a vertical line on the upper porcelin in line with the tan area of the plug. Screw it back into the head and see if the vertical line you made faces the exhaust valve(s).

The plugs are stock. The two different colors are split exactly to each side of the side electrode. One side is very tan and the other side is off white. It's almost as if you drew a line at the opposite side of the electrode and both plugs are the same.