Spark plugs that haven't been changed for a long time can become one with the cylinder head. Fortunately, it's possible to repair damaged threads instead of scrapping the head. (Photograph by Chris ...

There's something oddly satisfying about pulling an old spark plug out of an engine, but what do you do with the plug once it's out? Maybe you're having second thoughts about changing the spark plug ...

For hot rodders, spark plugs are often nothing more than inspection tools that reveal whether an engine is running too rich, too lean, or just right. Street guys look for a nice tannish-brown tint on ...