Whether you’re hauling heavy loads or chasing a quicker quarter mile pass, the factory components in a Cummins engine were designed for average use, not the extreme pressures of high performance.

Here are the five most common reasons we see engines fail, and how a D&J Remanufactured Long Block is engineered to outlast them all.

1. Connecting Rod Failure 

The Problem: Factory rods, especially the powdered metal versions found in newer 6.7L models, are prone to snapping or bending under high torque and cylinder pressure. When a rod lets loose, it usually takes the engine block… and your pride with it. Our solution, we don't just replace rods, we upgrade the design. Our long blocks often feature D&J Billet H-Beam or I-Beam rods designed to handle double (or even triple) the factory output. Each rod is weight matched and shot peened for maximum fatigue resistance.

2. Blown Head Gaskets & Lifted Heads

The Problem: High boost levels and heat cause the factory cylinder head to lift away from the block. Once that seal is broken, coolant enters the combustion chamber, leading to overheating and catastrophic failure. Our solution, we use CNC machined fire rings and heavy duty head studs. By machining a groove into the head or block and inserting a steel ring, we create a mechanical lock that can withstand 100+ PSI of boost without issue.

3. Dropped Valve Seats

The Problem: Over time, heat cycles can cause the factory valve seats to loosen and drop into the cylinder. This usually results in a destroyed piston and a cracked cylinder head in a matter of seconds. Our solution, every D&J head is thoroughly inspected and machined with oversized, high temp seats that are press fitted with a much tighter tolerance than the OEM standard. We ensure they stay where they belong, even under intense conditions.

4. Spun Main Bearings

The Problem: Under high RPM or high load scenarios, factory main bearings can shift or spin. This cuts off oil flow, creates massive friction, and effectively welds the crankshaft to the block. Our solution is precision, it is in our name after all. We perform line boring and honing on every block to ensure perfect crankshaft alignment. We also use high performance bearings with increased clearance for better oil film thickness, ensuring your engine stays lubricated when the heat is on.

5. Cylinder Wall Cracking & Scoring

The Problem: Thin cylinder walls in late model blocks can crack under extreme pressure. Additionally, wet liners or poor cooling can lead to cavitation and scoring, killing your compression. Our solution, we specialize in Deck Plate Honing. This process simulates the tension of a bolted on cylinder head during the honing process. The result? Perfectly round cylinders that stay round during operation, providing better ring seal, less blow by, and a much longer lifespan.

The D&J Difference: We don't just rebuild engines back to factory specs, we re-engineer them to fix the flaws the factory left behind. A D&J Long Block is a foundation built for power, reliability, and peace of mind.