A piston ring groove cleaner is a specialty scraper used during engine rebuilds. Over thousands of miles, oil burns inside the piston ring grooves, leaving behind hard carbon crust. If you put new rings into dirty grooves, the rings will bind, stick, or sit unevenly, causing low compression and heavy oil consumption. The groove cleaner clamps onto the piston body and uses a small cutter wheel to scrape this carbon out.
The cutter wheel has different teeth matching standard ring groove widths, like 1/16, 5/64, or 3/16 inches. Select the tooth that fits snugly without binding, adjust the tool tension, and rotate it around the piston. The blade shaves the carbon out, leaving a clean, flat channel. Be careful not to force the tool, as the cutter can scrape away the aluminum piston metal, widening the groove and ruining the piston.