When discussing diesel engines, one has to make mention that cylinder pressure is what makes the controlled “boom” happen. There are no spark plugs to ignite the fuel and air, so an exorbitant about of compression is the igniting source. This very high compression ratio (in the area of 22.0:1) can really strain the factory head bolts. Add into the mix any real performance enhancements and it will not take long to realize a blown head gasket because the OE torque-to-yield head bolts were not sufficient. When this happens, you learned the hard way that you should have installed a set of head studs.
If your engine is running fine, why should you consider head studs? With a torque-to-yield bolt, you torque the bolt to a specific torque and then, rotate it to a calculated amount, which is supposed to stretch the bolt a very specific amount. This creates the maximum clamping force of that fastener. However, this way of torquing can result in uneven pressure being applied.
With head studs, the “stretch” is not removed from the equation, but eliminating the torque-to-yield aspect does create a more uniform clamp pressure, and according to Kenny Thompson at KT Performance, “head studs do still have a small amount of stretch to them, but they are much better by design and stronger due to better material.” In other words, the improvements are by virtue of using a high-tensile-strength alloy and a stud rather than a bolt. The stud is threaded into the block by hand and then a fine thread nut is tightened/torqued on the top of the stud which results in a more precise torque of the head.
If you’re a smart diesel owner and you are planning to increase your engine’s output, the first upgrade you need to consider is a set of head studs. In fact, I know plenty of stock Cummins owners who feel upgrading to studs is a good idea. Basically, installing head studs is a good insurance policy.
I recently spent the day at Wrench’s Garage in Haines City, Florida as proprietor, Jake Lang, installed a set of KT Performance’s Gator Fasteners‘ head studs on a 6.7-liter Cummins. Gator Fasteners are manufactured using an 8740 nickel-chrome-moly produced for case hardening. It can often be found in aerospace applications, when wear resistance, toughness, and strength are needed. This means it’s going to hold up under some extreme abuse. In fact, the 10mm studs have a tensile strength of more than 221,000 psi.
From The Beginning
The truck being upgraded at the shop was not experiencing any head gasket “issues”, and the upgrade was to prevent any from presenting themselves. Since the head gasket was still good, Jake decided 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.
If you are upgrading head studs because you have already experienced a head gasket failure and want to prevent it from happening again, then your upgrade will require a bunch more work (head removal and machining, etc.). If you have a high-mileage engine or one presenting cylinder pressure issues, you should probably have the cylinder head removed and checked before installing the new studs. While adding head studs can reduce the risk of blowing a head gasket, they can’t cure a head gasket that is already blown.
Replacing the head studs in a Cummins-equipped truck is easily accomplished with the engine still in the truck. However, there is still some serious 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 this is a Cummins diesel, so it’s not quite that easy.
Making It Better With Head Studs
On the 6.7 engine, the EGR crossover tube will need to be disconnected and moved out of the way, The EGR cooler and other emissions parts, however, are not in the way. There is a multi-piece valve cover assembly that must be removed to get access to the rocker box that is under the valve cover. With the valve cover out of the way, you can access the injector wiring so the rocker box can be taken off. Next, the rocker arms will need to be removed which will allow access to the head bolts. While upgrading to head studs is not difficult, it does take some time, so plan on 6 to 8 hours. Two things I need to mention are, according to Thompson, DO NOT put lubrication on the bottom of the washer and Gator Fasteners does not recommend doing any hot re-torquing.
Another thing I need to mention is the rocker box will need some light modification. The head studs are physically longer than the factory bolts and as such, there is one small area of the rocker box that will need some minor clearancing. While this can be done with a rat-tail file, having a Dremel tool or a small die grinder with a carbide bit will definitely help.
Once you have the studs installed, put everything back together in the reverse of how you took it apart. If you plan to do the installation yourself, and this is your first time, plan on it taking all day or even a weekend to make sure that you’re not rushed. If the installation seems to be at all beyond your capabilities, have your local diesel performance shop perform the installation for you.
Finally, installing head studs will not increase power output, and it is not a guarantee that you will never blow a head gasket — things happen. However, it definitely makes it less likely that you will blow a head gasket when properly installed and torqued.