How To O-Ring a Cummins Head to Handle High-Boost Pressures
Circle of Confidence
Nothing beats the feeling of rolling a Dodge Ram pickup with a freshly compound-turbocharged Cummins diesel engine out of the shop and onto the street for the first time and experiencing the reward for the hours and dollars invested to gain a big bump in power. After making a few easy loops to get everything warmed up properly, you finally mat the throttle and feel all the torque come alive as the compounds do what they were designed to.
Everything happens simultaneously: The needle on the boost gauge rises to 20 psi and suddenly whips north of 40 psi as the turbos work their magic. Tires smoke. The exhaust cleans up. You’re pushed into the seat. Yes, everything is working better than you imagined. What a rush!
However, just when you think you’re now all set with brute power at your disposal any time your right foot is matted, boost suddenly falls and white smoke starts pouring from the tailpipe. The power is gone as quickly as it began, and the acidic smell of burning rubber filling the cab is replaced by the heartbreaking odor of hot oil and antifreeze coming from places it shouldn’t. Your rig’s compounded Cummins just blew the head gasket—or worse.
“We’ve seen a number of customers come through here over the years that have installed their own compound turbos and ended up having head gasket issues,” says Bill Allen, general manager of Source Automotive, an Oregon-based diesel-performance shop that specializes exclusively in Cummins. “They install ARP head studs and bolt on the turbos thinking all is well. Then they find out studs alone aren’t enough to hold the gasket in place when those boost pressures head north of 40 psi.”
While high-quality head studs add a needed level of engine durability, those who hot-rod 24-valve engines with compound turbos need to concentrate on taking measures on the head itself when boost pressures head north of 40 psi. If you don’t, head-gasket failure is guaranteed. That was the situation we found ourselves in with our Ford F-250 “Fummins.”
Our project rig’s salvage-yard ’00 5.9L powerplant had more than 200,000 miles on it before it was dropped into our Super Duty’s engine bay. Since we were on a tight budget, only basic upgrades were done. It was cleaned up externally, ARP cylinder-head studs replaced the factory bolts, and we ran it on an engine stand to make sure all was good before performing the transplant.
It held together with the big single turbo. But when the compounds were added, the head gasket blew out after the third hard pull on the dyno (about the same time the needle on the boost gauge flew past 40 psi). The expensive lesson we learned is that if you’re going to put compounds on any diesel, it’s imperative the head be prepared accordingly. Tight budget or not, this means having the head rebuilt and O-ringed to accommodate increased boost pressures. If the engine is out of the truck, the block should be addressed as well.
Prepping a used 24-valve 5.9L or 6.7L Cummins head for compound turbos involves surfacing the head, replacing valve guides, and cleaning the seats, as well as upgrading valves, seals, and springs. Once all of this is done, then the head is O-ringed.
We turned to Bearing Service Company in Portland, Oregon, an expert diesel-engine machine shop, for the rebuild portion. Owner Brian Schutzler says his company has specialized in engine rebuilding since 1929, and all the work is custom. They don’t cut corners when it comes to making sure the work is done with tight tolerances and extreme attention to every detail.
BSC’s work on our Cummins casting affirms this ethic. After Brian cleaned, Magnafluxed, and resurfaced the head (which was slightly warped and probably the cause of the initial gasket failure), technician Jacob Portillo handled the rebuild. Intake and exhaust valves were replaced with higher-quality versions, which Jacob trued before installation. “We do that to ensure they are perfect before assembly, because mass-produced valves can have some wobble. We take .001 to .002 inch off the face to make sure they are true,” the veteran machinist says.
Jacob also pays special attention to valve heights, cleaning out the oil-return passage and the injector hold-down thread holes so there are no issues during reassembly. He also checked our set of Mountain High Performance cryo’d 125-pound spring pressure rates and heights. “This is just your basic diesel head rebuild,” Brian says. “It’s nothing really special. We do a lot more exotic stuff when it comes to building an engine for sled pulling or drag racing.”
The two biggest upgrades done to our head were replacing the original valvesprings with 125-pound Mountain High Performance pieces and replacing all the valve stem seals with S.B. International’s Viton seals.
“On a head for any compound-turbocharged Cummins, we install top-hat–style seals because the valvespring itself holds them in position and will not allow the seal to fail from higher combustion temperature and boost values,” Bill says.
“We use the green exhaust material on our seals specifically for the higher temperature rating of high-horsepower diesel engines. As for the cryo-treated valvesprings with the increased seat pressure, again, we want to eliminate possible valve float or bind under the higher rpm and boost pressure owners see with the compounds.”
Source Automotive’s lead diesel technician Robert Gates handled the O-ring procedure using BHJ Products’ special O-ring register plate and cutter kit. The cutter is a crank-style, hand-operated device that attaches to a jig that is torqued atop the head. Both tools are precision-machined, with tolerances greater than .001 inch.
The O-ringing process is quite simple: A groove that’s aligned with the head gasket’s fire ring is cut in the face of the head, and then a stainless steel wire is inserted in the groove. But cutting grooves to the exact depth that’s necessary and deciding how much the wire protrudes above the fire deck is anything but simple. Experience plays a huge role in such factors.
BHJ offers a wide array of jigs and special heat-treated stainless wire for O-ringing diesel cylinder heads. BHJ’s Chris Ouellette says, “We tell Cummins customers they should get perfect results using .041-inch wire in .039-inch grooves and let them go their own way from there. We do recommend a protrusion of .006 inch (+/1 >001 inch) for MLS gaskets and .011 inch (+/- .001 inch) for composite Cummins B gaskets.”
Bill’s approach to O-ringing—step up one size, using .048-inch grooves set at a depth of .040 inch to hold .051 inch wire—stems from having more than a decade of experience in both building and racing 1,000-plus-horsepower, street-strip diesel rigs. This size groove supports a protrusion of .011 inch above the fire deck, so the wire bites into the fire ring without cutting so deeply that it affects the gasket’s structural integrity. Source Automotive says it has never experienced a gasket failure using that O-ring package on engines taking in more than 70 psi of boost.
Installing ARP StudsARP’s installation tips for PN 247-4202 (Cummins 24-valve 5.9L/6.7L cylinder-head studs): Use only ARP Ultra-Torque lubricant under the head of the bolt, or on the bearing surface of the nut, to ensure an accurate load clamp. Use Ultra-Torque on the stud ends that go into the block. Install the head first, then the ARP studs. Place ARP washers chamfer-side up. Never reuse ARP studs if they have stretched more than .001 inch. Torque sequence: 40 lb-ft, 80 lb-ft, and 125 lb-ft in sequential cycles using the standard clockwise sequence working outward from the two center bolts. If you retorque after the engine has run, do so with it no warmer than room temperature.
Source AutomotiveClackmas, OR 97015
BHJ Products Inc.Newark, CA
Mobile Diesel Service541-459-8939
Bearing Service Company503-222-1366
Mountain High Performance303-420-6218