Mercury - Marine Rotor for GM V6 (Delco HEI) Ignition 8504851 / 8M0062084. Overview. If you've ever worked on a marinized GM V6 with a Delco HEI ignition, you know the rotor takes a beating. It sits in a hot, cramped spot, shaking around while the boat moves, and dealing with moisture every single trip. When it starts to wear out, the engine usually shows it fast-little hiccups at idle, a miss when you throttle up, or that uneven feel you can't quite ignore. This rotor is built for that kind of