Cummins 4BT 3.9L Cylinder Head

3933370 | Cummins 4BT 8V Loaded Complete Reinforced New Cylinder Head | 3903920

Reinforce your engine with our redesigned Cummins 4BT 8V cylinder head, engineered to solve common cracking issues and valvetrain failure.

This is a brand-new, heavy-duty aftermarket casting specifically designed to be the “workhorse” of the industry. We have reinvigorated the 4BT head by making it thicker internally in crack-prone areas and utilizing a higher nickel content in the cast iron. Fully loaded and ready to install, this head is bred to outwork the rest.

🛠️ In-House Machining Process

• Debris-Free Preparation: Every new casting is chemically cleaned and blown out to remove all residual machining oils and manufacturing debris. This ensures your engine’s oiling system remains uncontaminated from the first start-up.
• In-House Precision Machining: Unlike “shelf-stock” heads, we perform all final machine work in-house. This includes final guide sizing and precision valve seat cutting to ensure perfect geometry and clearances.
• Pressure & Integrity Testing: To go beyond the factory standard, we pressure-test every head to 60 PSI. This verifies that the casting is free of porosity leaks or internal defects that could compromise the cooling system.
• Dimensional Inspection: Our technicians perform a multi-point inspection of the gasket-sealing surface. This ensures the head is perfectly flat and meets tight OEM tolerances for a flawless fit.
• Professional Assembly & Setup: Fully loaded with valves, springs, retainers, and valve locks. Includes new high-temp Viton valve stem seals and pre-installed standard size cam bearings for a true plug-and-play experience.
• Vacuum-Seal Verification: Every intake and exhaust port is Vacuum Tested. This guarantees a 100% airtight seal between the valves and seats, ensuring maximum compression and peak performance right out of the box.

📊 Technical Specifications

• Condition: Brand New Reinforced Casting
• Engine Compatibility: Cummins 4BT 3.9L (8-Valve)
• Displacement: 3.9L
• Year Range: 1984-2000
• Engine Type: Diesel
• Material: High-Nickel Content Cast Iron (Address cracking flaws)
• Seals: New High-Temp Viton Valve Stem Seals
• Includes: Valves, Springs, Retainers, Locks, and Cam Bearings (Standard Size)
• Compatible Part Numbers: 3933370, 3903920, 3932011, 3920005, 3966450, 3910275, 3800338, 3909947, 3904570

🚘 Common Applications

Direct replacement for Cummins 4BT 3.9L Engines found in:

• Step Vans / Delivery Trucks: Case, bread trucks, and industrial delivery units
• Agricultural Equipment: Tractors and various farm machinery
• Construction Machinery: Loaders, wood chippers, and stationary equipment
• Custom Builds: Popular for 4BT diesel swaps into Jeeps and classic pickups