GM Chevrolet 5.0L 305 Mercruiser New Cylinder Head – Casting Numbers 059 and 520 | 12552520 12558059 | No Core Required

GM Chevrolet 5.0L 305 & Mercruiser Marine New Cylinder Head – Casting #059 / #520

Marine-Grade Precision Rebuild – Fully Loaded and Ready for the Water

Restore your engine’s mechanical integrity with this brand-new GM 5.0L (305) Marine cylinder head. Engineered for the high-duty cycles of Mercruiser and Volvo Penta applications, this fresh, high-density castings are free from the thermal fatigue and corrosion common in used Marine cores. Every unit is precision-finished in-house, including final guide sizing and multi-angle valve seat cutting on our Rottler equipment to ensure perfect geometry. To guarantee a high-pressure combustion seal, the deck is PCD-milled on our Rottler S85A to achieve the ultra-low Surface Roughness (Ra) required for long-term gasket retention in moisture-heavy environments. These heads are pressure-tested to 60 PSI and undergo ultrasonic cleaning of all internal cooling passages to ensure maximum thermal dissipation and out-of-the-box reliability

🛠️ In-House Machining Process

• Cleaning: Fully disassembled and thermally cleaned.
• Soda Blasted: Castings are blasted with Sodium Bicarbonate. Because baking soda is water-soluble, there is zero risk of abrasive media clogging oil passages.
• Pressure Testing: Tested to 60 PSI to ensure no cracks or porosity leaks.
• Surfacing: All heads are resurfaced on our Rottler S85A for a precision gasket-sealing surface.
• Valve Job: Multi-angle valve job performed; every port is Vacuum Tested to ensure valves are seated 100% airtight.

📊 Technical Specifications

• Engine Compatibility: GM Chevrolet 5.0L 305 / Mercruiser Marine
• Casting Numbers: #059 and #520
• Assembly: Fully loaded with valves and springs
• Marine Optimized: Enhanced heat resistance and durability for salt and freshwater use

🚛 Fitment Data

Common Applications:

• Mercruiser Marine: 5.0L 305 V8 Engines
• Chevrolet/GMC C/K 1500 & 2500: 1996–1999 (5.0L)
• Chevrolet Express / GMC Savana 1500 & 2500: 1996–2002 (5.0L)
• Application Note: Ideal for marine rebuilds and Vortec-era small block truck repairs.