Rollers assure easy turning in cylinder. Exclusive stabilizer spring allows operator to take selective cut to minimize chatter. Spring-loaded carbide cutter follows contour of cylinder. Complete ridge removed in just a few easy turns. Offset jaw guides assure rigidity throughout the range When replacing pistons or rings, or whenever you're rebuilding or overhauling an engine, always remove the ridge that forms at the top of the cylinder. The pistons and rings will suffer damage if the ridge is left in place when the engine starts up for the first time.