Quicksilver - Idler Pulley MerCruiser V8 Series Flat 3.5-Inch Pulley 865444T. Overview. There is a certain comfort in hearing your engine belt spin smoothly, with no chirps or chatter. When the belt system is right, you can feel it in the throttle response, the steering assist, even the way the boat settles into its cruise speed. If your idler pulley is worn, the whole engine starts to sound unsettled. This Mercury Marine part brings that quiet confidence back. It is a small component, but it pl