Cummins diesel engines are known for their insane reliability over upwards of 500,000 miles. When it comes to doubling their horsepower, however, there are a few precautions to be taken. Besides the “killer dowel pin” problem, which we’ve covered in the past but will revisit soon, Cummins engines are also prone to blown head gaskets—a problem that can happen at any time. Unfortunately, head gasket reliability depends on how warped the Cummins head has become during many years and miles of driving. We’ve seen some trucks survive at 50 psi with nitrous, while other trucks start leaking at 200 rwhp with the fuel plate removed. It’s just the luck of the draw.
Even with some unknowns, there are still some things that you can do to stack the deck in your favor. After decades of use and thousands of heat cycles, head bolts lose their elasticity and the head gasket settles. This means that the head bolts that started out at 60 ft-lb and 90 degrees (about 120 ft-lb) might loosen up by 20-30 ft-lb or even more. Less clamping force also means it’s more likely that a blown head gasket will result from turning the power up, which we were about to do. The good news is that performing a re-torque, while time consuming, is fairly simple. Eventually, we’ll step up to a set of serious ARP 625 head studs and a fire-ringed gasket, but for the price (virtually free other than the ARP lube and labor), our Cummins re-torque was a pretty good deal.
The individual cylinder valve covers of the 5.9L Cummins were the next item on the chopping block, which was fine because we needed new gaskets. They were removed by loosening a single bolt for each one.
tbrown’s Diesel technician Gustavo “Goose” Quezada started by removing the engine cover on our stock, highmileage engine. There are a few things that need to be taken off in order to gain access to all 26 head bolts. The intake horn was the first item to be removed.
You can see here that the injection lines for the engine are also in the way when attempting a re-torque, so those would have to go.
Removing the injection pump lines really isn’t all that bad, but they should be removed as a group from the engine (as shown) and lifted off.
As you can see from this photo, the bolts started turning as we re-tightened them, indicating that they did indeed loosen up as compared to the factory specifications.
It may look like a cheat, but torquing the bolts to 125 ft-lb yielded about the same amount of twist to all the head bolts—about 1/8 of a turn. If any turned a quarter turn or more, we’d also have to recheck our valve lash. With our newfound clamping force, we’re ready to move on to Scheid Diesel’s 5x0.018-inch injectors!
Once the bolts were marked, we loosened a single bolt until we could get under it, lubed it with ARP assembly lube (including the washer), and then re-tightened it before moving to the next one. Make sure to perform this step one bolt at a time because if you loosen all of them at once, your gasket will lose its seal.
Here we provided the factory head bolt torquing sequence to show you the right order to re-tighten each bolt. This is done to ensure an equal clamping force on all parts of the head gasket.
The return line for the injectors also was taken off, which was fine because injectors would be our next step.
Now the fun part. We marked all the head bolts with a yellow paint marker to see how much they would turn. If one bolt is turning way more than any other it would mean that it’s losing its elasticity, which could spell trouble.
There are many theories about the best way to re-torque head bolts including creeping at 5 ft-lb increments (which tries to “cheat” the bolt’s elasticity), but we chose to mirror the factory method by torquing each bolt to 60 ft-lb and then going straight to 125 ft-lb.