The outer valve spring K 27504 is a heavy-duty, precision-formed coil that works as the primary retaining spring for both inlet and exhaust valves in the Sulzer ZV40/48. Designed to sit outside the inner spring (when fitted as a nested pair), the outer spring takes the brunt of high-load cycles, helps control valve rebound and aids in damping at high engine speeds. Made from fatigue-resistant spring steel and heat-treated for long life, K 27504 is critical for consistent valve seating and timing — inspect for coil relaxation, cracking or loss of free length during overhaul, because worn outer springs lead quickly to valve float, poor combustion and accelerated component wear.