Changing spark plugs is standard maintenance on gasoline-powered cars. Can you clean and reuse old spark plugs, or should you go for brand new ones?

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 ...

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 ...