GM Chevrolet 5.0L 305 Mercruiser Cylinder Head – Casting Numbers 059 and 520 | 12552520 12558059

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

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

Restore the power of your GM 5.0L 305 or Mercruiser marine engine with these high-quality remanufactured cylinder heads. Specifically designed to withstand the harsh demands of marine environments—including extreme heat and moisture—these heads are engineered to meet or exceed OEM specifications for a perfect factory fit.

🛠️ 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.