Cylinder pressure in diesel is essentially what makes the power. And there are several variables that lead to increased pressure, such as adding more fuel and boost. Toss in today’s common rail injection sequences and factory torque-to-yield head bolts, and you can see why cranking up the power can pop a head gasket, or worse.

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In addition to performance tuning, fuel system, intake and exhaust upgrades, if you own a 6.7L Cummins a set of head studs should be on your “to-do” list. The ARP CA 625 head studs are individually wrapped to protect them in transit and come with nuts, washers and assembly lube.

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1. & 2. To start the installation, Chase Fleece removes decorative trim panels and the multi-piece valve cover.

3. This EGR tube also needs to be temporarily removed to make way for the stud installation.

4. After disconnecting all of the fuel injector harness leads, Fleece removed the injector assembly and set it aside.

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5. & 6. Fleece next unbolted and removed the rocker box assembly, digging further into the top of the head.

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7. & 8. Finally each pair of rocker arms was removed from the head along with the push rods and valve bridges. Be sure to set them down in order so that they can be reassembled in their original positions.

9. After removing two of the factory head bolts at a time, Fleece replaces them with the new head studs from ARP. He uses an electric ratchet to run them into the block, but they’re only installed hand tight; it’s not necessary to torque the studs into the block. Additionally, be sure to install the six longer 6.625-inch studs in the locations along the exhaust manifold on the cylinder head outside of the valve cover.

Smart diesel owner/builders who plan on upping the power ante via more fuel and boost typically use a set of head studs to ensure even clamping force between the cylinder head, head gasket and block, as well as reducing any chance of head bolt “stretch” under high-boost circumstances. Racers have been using head studs for years for their even clamping force, and more and more owners of street-driven diesels, especially those with Cummins 5.9 and 6.7L motors, are installing head studs as an insurance policy. And on the 6.7L, many builders attribute the larger pistons in the 6.7L Cummins for upping cylinder pressures even more.

A simple and relatively easy cure for head gasket failure prevention is to install a set of head studs from a high-quality manufacturer like PureFlow/AirDog, whose Anthony Reams is in the process of building the ultimate shop truck. Reams wanted to provide some additional insurance for the head gasket in his 2012 Ram 2500 since he’d be turning up the power with a whole host of aftermarket modifications.

Reams turned to the folks at Automotive Racing Products a.k.a. ARP for a set of the top-of-the-line Custom Age 625 head studs and then headed north to Brownsburg, Indiana, to Fleece Performance Engineering for the installation. Since the head gasket was still good in Reams’ truck, the folks at Fleece were able to swap out the stock head bolts for the new head studs one at a time without removing the head or replacing the head gasket.

On the other hand, if the head gasket is blown, or there’s even the slightest inclination it may have gotten hurt in some high-boost runs, then further diagnostics may be necessary including the cylinder leak-down test. A good rule of thumb is when in doubt, yank it out. High-mileage engines or ones with cylinder pressure issues should have the cylinder head removed and checked, including decking, before installing a new head gasket. Think about studs as preventative medicine. They will help reduce the risk of blowing a head gasket, but won’t necessarily cure a head gasket that has already blown.

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10, 11 and 12 ARP supplies two packets of their proprietary Ultra-Torque fastener assembly lubricant with each set of head studs. The lubricant allows the fasteners to be tightened to the proper torque value without binding and provides accurate torque measurement. Fleece applies Ultra-Torque to the faces of the washer and nut as well as the threads of the stud.

13. Fleece starts each nut by hand to make sure that the threads are properly engaged before running the nuts down on the studs.

14. Before moving on to another pair of bolts and repeating the process, Fleece torques the nuts to 150 ft-lb in three equal steps as recommended by ARP. Be sure to use a high-quality torque wrench so that you get accurate and consistent torque results.

15. After all of the head bolts are replaced with the ARP studs and properly torqued, Fleece reinstalls the push rods, valve bridges and rocker arms, and then adjusts the valve lash setting at .010-inch on the intake and .020-inch on the exhaust valves.

16. Then he installed the rocker box and fuel injector harness, being careful not to over-tighten or cross-thread the harness nuts on the fuel injectors.

17. Fleece installs the multi-piece valve cover to complete the job.

ARP makes head studs for the Cummins engines in standard and Custom Age 625 materials. The standard studs are a great upgrade to replace factory head bolts and will handle being torqued tighter than the factory bolts, making them a good alternative for budget-minded diesel enthusiasts who are not pushing the power limits too hard in daily-driver trucks. For those like Reams who plan to push the limits harder, it’s best to go ahead and spend more initially and go with the stronger CA 625 studs to begin with since they can be torqued even higher than the standard studs to make it even more difficult to lift the head and blow a gasket.

On a Cummins-equipped truck, the studs can be installed with the engine in the vehicle, but there’s still a good amount of disassembly required to get far enough down into the head to replace the factory bolts with the new studs. It would be nice if you could simply remove the valve cover and swap the bolts for the studs, but unfortunately you need to dig down deeper than that to even reach the head bolts.

On the 6.7L truck the multi-piece valve cover assembly must be removed and you may even have to temporarily remove some parts of the emissions system that interfere with access to the cylinder head. Then the fuel injector wiring harness must be removed along with the rocker box and even the rocker arms themselves just to reach the head bolts. Without a doubt, installing head studs is a labor-intensive job that will get some grease under your fingernails, but the resulting longevity and peace of mind when pushing the truck hard are well worth it.

It took veteran diesel tech Chase Fleece nearly a full day to install the head studs along with the typical photographic slowdowns. If you plan to do the installation yourself, be sure to set aside a long day or even a weekend to make sure that you’re not rushed and are able to do the job right. If the installation seems to be at all beyond your capabilities have your local diesel performance shop perform the installation for you.

Follow along over the next few pages to see an overview of the installation on Reams’ Ram 2500. Diesel performance experts like Chase Fleece and the team at Fleece Performance Engineering recommend installing head studs on your 6.7L Cummins whenever you plan on pertformance upgrades and tunes to help minimize the risk of blowing head gaskets. If you do it before you have problems it really is cheap insurance compared to the downtime and expense you will pay to repair a blown head gasket.

Installing head studs is not a guarantee that you will never blow a head gasket, but it sure makes it less likely that you will blow a head gasket when properly installed and torqued. Remember that installing head studs won’t help your truck make more power, but they will help keep the power that you make inside the combustion chamber where it belongs! DW

SOURCES:

Automotive Racing Products (ARP)
Dept. DW
1863 Eastman Avenue
Ventura, CA 93003
800-826-3045
www.arp-bolts.com

Fleece Performance Engineering
Dept. DW
468 Southpoint Circle
Brownsburg, IN 46112
855-839-5040
www.fleeceperformance.com