Quicksilver - Idler Pulley MerCruiser V6 & V8 Series 6-Groove Pulley Design 864625T. Overview. Every boater knows the importance of a quiet, well-behaved serpentine belt system. When the belt tracks straight, tensions properly, and runs over smooth pulleys, the whole engine feels calmer. But when an idler pulley starts to go, you hear it - that faint chirp, that slight vibration, that little reminder that it's time for fresh hardware. This Mercury Marine part replaces that uncertainty with confi