Mercury - Quicksilver Serpentine Belt Idler Pulley For MerCruiser Engines 807757T. Overview. Smooth, steady belt operation keeps your boat's vital systems running right - and the Mercury Marine 807757T Quicksilver Idler Pulley helps make that happen. Designed for MerCruiser 4.3L, 5.0L, 5.7L, 6.2L, and 8.2L sterndrive and inboard engines made by General Motors, this OEM pulley guides the serpentine belt while maintaining proper tension and alignment. Made from a durable thermal resin with an inte