* Rotating a bolt: Many tensioners use a bolt that, when rotated (often clockwise), moves the tensioner pulley away from the belt, allowing you to remove the belt. This bolt might be 18mm, but you'll need a way to *hold* the tensioner in place while you rotate the bolt. A wrench on the bolt and a long screwdriver or pry bar wedged against the tensioner assembly to keep it from spinning is often used.
* Using a tensioner pulley tool: Some tensioners require a special tool to compress or move the pulley. This is a purpose-built tool that fits the tensioner design. An 18mm wrench will not work here.
In short: You need more than just an 18mm wrench. You'll probably need either a second wrench to hold the tensioner, a pry bar, and possibly a specialized tool. Before you start, consult a repair manual specific to your 1992 Buick Skylark 3.3L V6. The manual will show you exactly how the tensioner is designed and the correct procedure for removing the belt. Improperly attempting this can lead to injury or damage to the tensioner or other components.
