Mercury - Quicksilver Serpentine Belt Idler Pulley L6 Verado / QC4V Series Thermal Resin 8M6003035. Overview. Anyone who's spent long days offshore or cruising the back bays knows how much you depend on the quiet, constant rhythm of your engine. The Quicksilver 8M6003035 Serpentine Belt Idler Pulley is one of those behind-the-scenes parts that keeps everything moving smoothly-literally. It's the kind of component you rarely think about until the day it fails, and that's exactly why boaters trust