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 ...

Replacing your spark plugs is important and usually a fairly simple process, but if they seize in the cylinder heads it's an entirely different matter.

Along with swapping out the air filter and changing the oil, replacing the spark plugs is one of the few things left that require service on a modern gasoline engine. Some newer than the twenty-year ...