this...

only one plug looked like this, all the other ones were normal. What conditions would cause this and why would they only occur in one cylinder? (it's #1 if that's important)

Thanks.

 

I think the only thing that would cause that is detonation. Improper timing, too low octane, or not enough cooling to that cylinder can all be reasons for that.

GP

 

gpierce pretty much covered it, the temps get too hot and the fuel/air mixture pre-ignites, will often cause serious damage to an engine. If you have a lot of carbon build up in your cylinders it may be retaining enough heat to do that. if you have higher than stock compression you should probably be using premium.

 

Thanks guys! Maybe there is enough build up in that cylinder to cause this. Possibly a bad valve? I notice that it idles rough, apparently at random. That's why i checked the plugs in the first place.