Mercury - Valve Spring Kit 357 CT Iron Heads Precision Steel Components 8M0120862. Overview. Anyone who's spent time around a circle track engine knows there's a rhythm to performance-an even, confident pulse that tells you the valvetrain is working exactly as it should. When that rhythm slips, even just a little, you feel it right away. That's why replacing worn components with trusted parts matters so much. The Quicksilver 8M0120862 Valve Spring Kit brings back that steady, responsive feel tha