For any engine builder, the moment of truth often comes down to the final click of a torque wrench. It’s a process built on trust—trust in your tools, your measurements, and the parts you’re installing.

In a recent video uploaded by BoostLine Products on their YouTube channel, Adam Horwatt from the Race Winning Brands R&D team walked through this exact process.

He demonstrated the thorough assembly of a Cummins 5.9-liter 6BT engine featuring BoostLine’s new connecting rods. Their goal? Well, they want to make over 2,000 lb-ft of torque.

The Importance of Pre-Assembly

The video begins not with final assembly, but with a critical pre-assembly step. Adam explains that this is a chance to check bearing clearances and, more importantly, to verify rod bolt stretch.

He calls it a “recommended extra step using stretch gauge to ensure proper fastener clamping force, as torque wrench calibration can vary in the field.”

The process involves torquing the high-quality ARP rod bolts to the spec sheet’s 135 lb-ft, and then using a stretch gauge to confirm the bolt has stretched between 6.5 and 7.0 thousandths of an inch.

If it hasn’t, the torque value is adjusted until that precise stretch is achieved, guaranteeing the correct clamping force.

Piston Assembly and Installation

Once the rods are prepped, the video moves to the piston assembly. Adam highlights another critical detail for builders: “Rod orientation is important for proper assembly, so make sure that the serial number side of the rod is opposite the piston sprayer notch in the piston.”

After carefully installing the wrist pins and retaining clips, the piston and rod assemblies are lubricated and slid into the cylinder bores using a ring compressor.

The rod caps are then installed and torqued to the specific value that was determined during the bolt stretch test. Finally, a quick spin of the crankshaft confirms that everything should rotate without binding.

Dyno Built Cummins 5.9-liter 6BT

This step-by-step process shows that building a Cummins 5.9-liter 6BT engine to handle 2,000 lb-ft of torque is more than just using strong parts. It’s about the precision and care taken during assembly.

Every measurement, every drop of lube, and every final torque sequence is what gives a builder confidence that their new engine will hold together when it’s finally time to make some real power on the dyno.