Pushing big boost on a 6.7-liter Cummins is fun until the head gasket lets go. To prevent that expensive and catastrophic failure, installing a set of ARP 625 head studs is the go-to insurance policy for any high-power build. A video from CF Diesel recently broke down the entire tedious, but essential, process of swapping them in without pulling the head.

Teardown And Meticulous Prep

The installation began with a careful disassembly of the top end of the engine. To get access to the factory head bolts, the builder first removed the injector harness and the cast aluminum rocker box. From there, the rockers and valve bridges were pulled, with the video emphasizing the importance of keeping every single component organized by cylinder number to ensure the valvetrain went back together exactly as it came apart.

The One-at-a-Time Method

With the factory head bolts exposed, the core of the job began: replacing them one at a time. Each factory bolt was removed, and a new ARP stud was threaded in by hand until it bottomed out in the block. The video highlighted an important step often missed by first-timers: backing the stud out a half-turn to see to it that it isn’t bottomed out under tension. After applying ARP’s assembly lube, the nuts were torqued in a specific sequence over three separate passes: 50, 100, and finally 150 ft-lbs. This process ensures an even clamping force, which is why the ARP 625 head stud is the top choice when it comes to performance builds.

Notching The Rocker Box For The ARP 625 Head Stud

One part of the job that might catch some installers by surprise was the required modification to the rocker box. An internal cast gusset, located near cylinder number six, interfered with the larger 12-point nut on the new studs. Using a die grinder, the builder carefully notched out the gusset to provide the necessary clearance, stressing the need to thoroughly clean out any metal shavings before reinstallation to avoid engine damage.

The Foundation For Big Power

With the studs torqued and the rocker box having the right clearance, the valvetrain could be reinstalled. The job isn’t truly finished until a valve lash adjustment is performed and a final hot retorque is completed after the engine has run through a full heat cycle. This in-depth installation provides the bulletproof foundation every high-boost Cummins needs, giving owners the confidence to push their trucks to the limit without fear of lifting the head.