You just spent months planning your build. You’ve invested in a D&J Precision Machine Enforcer Series long block, a high flow cylinder head, and the best fueling components on the market. The engine is finally sitting in the frame, and you’re ready to hear that Cummins purr. 

Before you go out and try to set a new record on the dyno, there is one final, critical step: The Break In.

The first few hours of an engine's life determine whether it will live a long, high horsepower life or suffer from premature blow by, oil consumption, and power loss. Here is how to do it the D&J way…

Why the Break In Period is Not Optional

Modern machining is incredibly precise, but on a microscopic level, your new piston rings and cylinder walls still need to "mate." This process, called seating the rings, requires controlled friction.

If you baby the engine too much, the cylinder walls can glaze over, meaning the rings never fully seal. If you beat on it too hard, too soon, you risk scuffing the parts before they’ve had a chance to settle.

Step 1: Pre Fire Essentials

Your D&J engine arrives pre-lubricated with VR1 20W-50 race oil. This is a high zinc mineral oil specifically chosen because it provides the right environment for components to wear in safely.

• Verify Pressure: Before you ever let the engine fire, unplug the injectors and the fuel supply pump. Crank the engine until you see oil pressure on a mechanical gauge. This ensures oil is reaching the bearings and turbo before they are under load.

• Dry Start Warning: Do not fill the radiator with coolant yet (hold on, we’ll explain why in a second).

Step 2: The First Five Minutes (Setting the Rings)

Start the engine and immediately bring the RPM up to 1,800 RPM. Hold it there steady for five minutes.

Why no coolant? Running without coolant for this very short window allows the cylinders to quickly reach operating temperature, which is essential for the piston rings to expand and seat against the crosshatch of the cylinder walls.

• Note: Do not let the engine idle. Idling is the enemy of a new engine; it causes glazing and hinders camshaft break in.

Step 3: The Cooling System Burp

After five minutes, turn the engine off and check for any leaks. Once the engine has cooled, you can fill it with coolant.

Pro Tip: Leave the heater core hose off the top of the cylinder head while filling. This allows air to escape, ensuring the head is completely full of coolant with no trapped air pockets that could cause potential hot spots.

Step 4: The Twenty Minute Heat Cycle

With the coolant now full, start the engine again and return to 1,800 RPM for twenty minutes. Keep a close eye on your gauges. This step brings the entire block up to a stable operating temperature and allows all components to heat cycle together. Remember to avoid excessive idling.

Step 5: The Hot Re-Torque

This is the step most DIY builders skip, but it’s the most important for the life of your head gasket. After your twenty minute run, turn the engine off, drain the oil, and perform a hot re-torque of the head studs while the engine is still warm.

• D&J Standard Studs: Re-torque to 125 ft-lbs.

• D&J 9/16" Studs: Re-torque to 175 ft-lbs.

• Sequence: Always start in the center and work your way out. This is also the perfect time to check and reset your valve lash (.010" Intake / .020" Exhaust).

Step 6: The First 500 Miles

Once the re-torque is done and fresh break in oil is added, you’re FINALLY ready for the road.

• Vary Your Speed: Do not jump on the highway and set the cruise control. Varying your RPM and load helps the rings seat across the entire powerband.

• Moderate Load: Don't be afraid to give it some throttle (moderate boost), but avoid max effort runs until you’ve cleared the 500 mile mark.

Summary Checklist

1. Pre-lube until oil pressure is confirmed.

2. 5-minute run at 1,800 RPM (No coolant).

3. Fill coolant (Bleed air from the head).

4. 20-minute run at 1,800 RPM.

5. Drain oil & Hot Re-Torque head studs.

6. Check Valve Lash.

7. Drive 500 miles with varying loads.

Still have questions about your specific build? Give us a call or check out our full Break-In Procedure guide on the website.