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How to give a Cummins 5.9L 12 valve a second life

Dunks Performance’s Thorough Rebuild Improves the Power, Longevity, and Fuel Economy of a 12-Valve 5.9L Cummins Diesel

Bruce W. Smith
May 1, 2016
Photographers: Bruce W. Smith
First it was a simple oil-cooler failure. A week later, Adam Metter noticed his ’97 Dodge Ram 3500’s 5.9L Cummins engine developed a knock, as the dualie pulled a heavy trailer over a mountain grade. Although the odometer on Adam’s primary heavy-haul work truck had just rolled past 244,000 miles, he always kept the big Ram well maintained inside and out. So, as you can imagine, the knock was disconcerting.
A few days after Adam dropped the pickup off at family owned Dunks Performance in Springfield, Oregon, lead technician Eric Dunks called with the bad news: the Number Six cylinder showed signs of piston scoring. The 20-year-old Cummins needed a rebuild.
Cummins engines have a strong reputation for being built to last far longer than the trucks they power. However, Don Southworth, one of the owners of Eugene, Oregon-based engine shop Southworth Inc., says he sees scored rear cylinders in the older I-6 powerplants quite often.
“The Number Six cylinder is the most prone to overheating and losing clearance between piston and cylinder wall,” Don says. “I’ve seen this happen on 5.9Ls with low miles and high miles. It’s not a mileage issue. It’s related to a rapid heat buildup in the rear two cylinders and the way coolant flows [front to rear] in the block.”
With more than 340,000 ’94-to-’98 Dodge Ram 2500 and 3500 pickups running second-generation, six-cylinder B-Series (6BT) Cummins engines, there’s a good possibility other owners of these workhorses are, or will be, in the same situation as Adam.
In this report, we’re following the ’97 Cummins through the rebuild process and providing insights for other Dodge Ram owners about how to give a worn-out Cummins 5.9L new life.
Clean, Inspect, Measure, and Machine
Dunks sent Adam’s 6BT to Southworth Inc. for a thorough cleaning, pressure test, Magnafluxing, machine work, and a short-block rebuild. What Southworth machinists found is common with many of the Cummins engines that come in their shop with nearly 250,000 miles: very little internal wear.
The head received a clean bill of health, having no cracks between the valve seats, no leak-down, and flatness end to end and side to side on the face. The block is just as sound, with no cooling system cavitational pinholes in the cylinder walls, a flat deck, and all the rotating parts still within Cummins specs. Adam’s engine shows the benefit of sticking to a preventative maintenance regimen, using quality filters, and being diligent on oil changes.
The only area of concern is the rearmost cylinder, which Don says shows the obvious signs of a “high heat moment” causing the piston to scrub the cylinder wall. Preliminary inspection shows the scored cylinder will clean up by boring and honing it out 0.020 inch, using a torque plate to duplicate the same load and cylinder distortion of an engine with the cylinder head installed. Doing this ensures the bores will be perfectly round.
Southworth’s machinists also bore the problem cylinder 0.001 inch larger than the other five holes to give that piston extra clearance in the event of future high-heat moments. They also pay very close attention to valve recession and piston protrusion, marking the protrusion number on the top of each new piston. (This block’s piston protrusion varied between 0.019 and 0.021 inches, and the piston-to-valve clearance of each cylinder fell between the 0.039 and 0.060 inch, per Hamilton Camshafts’ specifications.
In addition to the ARP head studs, Adam chose Mahle pistons with marine-style bowls and a Hamilton 178/208 camshaft (0.290-inch intake/0.320-inch exhaust), so making sure the piston-to-valve clearances are within Cummins’ tolerances is even more crucial to maximize this 6BT’s performance and longevity. Because Adam wants his “new” 5.9L to have more power, better fuel economy, more durability, and better overall driveability than it did when it was removed from his truck, the pistons and cam are the first step toward achieving that goal.
Adding Power Parts
Adam consulted with Eric, his brother and shop owner Mike Dunks, and several aftermarket manufacturers before settling on other replacement components that will work in harmony with the new cam and pistons.
He takes one step up the 6BT performance ladder from intake to exhaust by adding Banks Power’s TwinRam intake; a BD Diesel Performance Cam Plate kit, downpipe, stainless one-piece exhaust manifold, and 60hp injectors; Fleece Performance Engineering’s Coolant Bypass; and a 4-inch Diamond Eye exhaust system.
This combination should boost the 12-valve Cummins’ power from a modest 215 hp/440 lb-ft to about 400 hp/820 lb-ft, while keeping exhaust gas temperature well within a safe operating range—even while towing heavy loads.
Adam’s Dodge Ram 3500 should also get better fuel economy in the lower rpm, run cleaner, and have considerably better all-around throttle response and driveability. That’s a good combination for any diesel-powered work truck.
Cam Plate Mods
Replacing old technology with new is just one aspect of doing a 6BT rebuild the right way. The other is continuing the inspection process as those new parts are being bolted in place. Eric says if you are reusing the original oil cooler it should be pressure-tested and flushed out with solvent to ensure it’s squeaky clean before being reinstalled. “I recommend pressure-testing new ones, too,” the certified Chrysler technician says. “It pays to be over cautious.”
Eric also recommends replacing the P-pump’s fuel solenoid if it looks like it’s the original part and adjusting/replacing the fuel-stop plate (“cam plate”) while they are easy to reach. The solenoid on Adam’s engine was fairly new, but Eric discovered the cam plate had been ground flat, which is a popular backyard method for maximizing a 12-valve Cummins’ power.
That modified plate might have contributed to the Number Six cylinder’s heat issues. “While this modification adds more fuel and therefore increases power, it also produces excessive black smoke (from unburned fuel) while elevating EGT under load,” says Cam Rose, a customer support technician at BD Diesel Performance.
“The fuel plate’s profile is the thing that schedules fuel delivery, so different plates are suitable for different injection pumps and power levels. A ‘zero’ plate will not give you an ideal fuel curve. So, although the truck will go faster, it won’t perform as well or run as clean as it will with a properly chosen fuel plate. Fuel economy will be compromised, too.”
Eric replaces the modified “zero” plate with the custom-profile unit from BD. He also takes a close look at the P7100 pump’s throttle-stop adjustment screw to make sure the head isn’t flattened from decades of use. “Sometimes, the soft metal head of the stop gets beat down, making it difficult to adjust the idle. Now is the best time to adjust or repair it.”
Finishing Touches
Having the Cummins I-6 sitting out in the open is also the ideal time to install a coolant bypass, which Eric does using Fleece’s kit. He also replaces the rear main seal, which gets brittle with time and miles, cracks, and starts seeping.
At the front of the engine, a new oil pump is installed and Eric makes sure the 5/16-inch steel dowel pin that helps align the aluminum front timing cover has the retainer to keep the pin from vibrating out and falling into the timing gears. “If you have a 6BT without the ‘killer dowel pin’ kit, put it in,” Eric says.
The cylinder head is set in place and Eric installs the ARP studs by hand until they just barely touch the bottom of the block. Then he reverses them out about an eighth of a turn. He checks the head closely to make sure no injector coppers (washers) have been accidentally left in the head before installing BD Diesel’s marine 370hp injectors. “It’s easy to miss an old copper and lay a new one on top,” Eric says.
From there, it’s the normal reassembly process, cleaning and replacing stock parts, bolting on the new performance items, torquing fasteners to specification, and double-checking everything. The rebuilt 5.9L looks impressive with its new turbo, intake, exhaust manifolds, and plumbing.
Of course, it will be even more impressive when the ignition key is turned. After a new Diamond Eye exhaust system and BD Diesel Performance’s exhaust brake and downpipe are installed, along with a new South Bend twin-disc clutch, Adam will be back on the road, driving a 20-year-old Dodge Ram 3500 that can run right alongside the new ones and be as reliable as a sledgehammer while doing it.
Photo 2/26   |   002 Cummins 6BT Rebuild Bad Piston
The Number Six piston (left) in Adam Metter’s ’97 Cummins 5.9L engine suffered a “high-heat moment,” resulting in the loss of sufficient piston-to-cylinder clearance. The discoloration on the inside of the piston skirt confirms this, according to Don Southworth of Southworth Inc., a Eugene, Oregon-based engine rebuilding/machine shop that is doing the repair work on Adam’s 12-valve. While the engine has nearly a quarter-million miles on it, the other pistons look like new.
Photo 3/26   |   003 Cummins 6BT Rebuild Cylinder Damage
This photo details exactly where the piston was making contact with the cylinder wall.
Photo 4/26   |   004 Cummins 6BT Rebuild Measuring
After Don cleans the block and cylinder head, they both undergo a very thorough inspection inside and out, which includes Magnafluxing, pressure tests, and measurement of all the surfaces to see which of them need attention. Even with more than 244,000 miles on the odometer, the rotating assembly in Adam’s engine is still within factory specifications.
Photo 5/26   |   005 Cummins 6BT Rebuild Oil Squirter
One easily overlooked part in the 5.9L short-block rebuild is the plastic piston oil squirters, which can become clogged or fall out. Don replaces the old ones with the same factory-green Cummins versions to ensure the pistons are properly cooled.
Photo 6/26   |   006 Cummins 6BT Rebuild Torque Plate
A torque plate is an important tool that’s used for boring and honing any Cummins 5.9L block. By ensuring each hole will be perfectly round and within specifications while under the stress of head studs that are torqued with 150 ft-lb, the plate helps eliminate the possibility of there being piston-to-cylinder clearance issues during the engine’s final assembly.
Photo 7/26   |   007 Cummins 6BT Rebuild Surfaced Block
Here’s Adam’s 5.9L Cummins short-block. The deck is lightly surfaced, and the block is fitted with new bearings and Mahle 0.020-inch-overbore marine-style pistons. Don says the original crankshaft and rods are still like new, so they’re being reused, as are the old freeze plugs (unless there’s something wrong with one).
Photo 8/26   |   008 Cummins 6BT Rebuild Mahle Piston
Mahle Performance marine-style bowl pistons measure 64 mm (2.52 inches) across with 47.1 cc volume while stock 5.9L Cummins measure 52 mm (2.02 inches) with 44.5 cc volume. Note: Don hones the Number Six cylinder 0.001 inch larger (creating 0.007 inches of piston-to-cylinder clearance) than the others to compensate for extra heat around that cylinder. Mahle’s specs call for cylinders 1 through 5 to have between a 0.0055- and 0.0065-inch clearance. The number written on top of the piston indicates the amount it protrudes above deck surface, which for this cylinder is 0.0195 inches.
Photo 9/26   |   009 Cummins 6BT Rebuild Hamilton Cam
A good towing/fuel economy camshaft for the 12-valve Cummins is Hamilton Cams’ Part Number 178-208 (0.290-inch intake/0.320-inch exhaust lift). It moves a lot of air at low rpm, and the short duration and wide lobe-separation angle help reduce EGT and spool the turbo quicker. The cam makes part-throttle operation better throughout the entire rpm band, too.
Photo 10/26   |   010 Cummins 6BT Rebuild BD Turbo
Along with the new cam, Adam’s upgrade includes BD Diesel Performnace’s Super B turbo, which flows 270 cfm more air than the stock Holset HX35W and 2 to 5 more psi of boost, adding about 120 hp with no other modifications. The Super B provides our rebuilt 6BT quick spool-up, cooler EGT, and no surging. It's ideal for towing and all-around highway use.
Photo 11/26   |   011 Cummins 6BT Rebuild BD Boost Control
The turbo comes with a replacement fitting (left) for the boost-control actuator. The restricted orifice increases boost pressure up to 5 psi by delaying the ingress of air into the wastegate actuator. Then some of this pressure is allowed to bleed off to the atmosphere through the small hole in the side of the elbow.
Photo 12/26   |   012 Cummins 6BT Rebuild BD Intake
Adam is replacing the stock exhaust manifold with BD’s one-piece stainless version, which has far better flow characteristics and is matched to the Super B turbo. Improved exhaust flow promotes faster throttle response, added power, and lower EGT. Stainless steel is much more thermally stable than cast iron, so it doesn’t expand and contract nearly as much, and it holds the heat rather than wicking it into the engine bay.
Photo 13/26   |   013 Cummins 6BT Rebuild ARP Head Stud
Eric installs the ARP studs by screwing them in fingertight first, then backing off a fraction so they are not bottomed out.
Photo 14/26   |   014 Cummins 6BT Rebuild Eric Dunks
Eric finishes the manifold and turbo installation on Adam’s ’97 5.9L Cummins 12-valve engine.
Photo 15/26   |   015 Cummins 6BT Rebuild BD Cam Plate
A common modification to older Cummins powerplants like this 6BT is grinding the P7100 injection pump’s stock cam plate until it is flat (right.). This is often referred to as a “zero” plate, and the process is a backyard method of increasing fuel delivery from the injection pump. However, a zero plate increases EGT and pours on the fuel all the time, so it’s not good for towing or fuel economy. The stair-step-like profile of BD’s Number Ten fuel plate (left) is designed to add about 100 hp and improve fuel economy over a stock plate.
Photo 16/26   |   016 Cummins 6BT Rebuild Throttle Stop
While inspecting and upgrading the P-pump, don’t forget to take a close look at the head of the idle-adjustment screw, which can flatten over time, making it difficult to adjust. Replace or repair as necessary.
Photo 17/26   |   017 Cummins 6BT Rebuild Fuel Solenoid
Eric recommends replacing the pump’s fuel solenoid with a new one if it appears to be the original. This one on Adam’s 5.9L was replaced by Dunks a few years earlier, so it doesn’t need replacing.
Photo 18/26   |   018 Cummins 6BT Rebuild BD Injector
Along with Mahle pistons, the BD Super B turbo, and Hamilton cam, Adam’s 6BT is also receiving BD’s 60hp injectors. The bigger injectors are actually Marine 370 units and work well when combined with the other minor modifications being made to this engine.
Photo 19/26   |   019 Cummins 6BT Rebuild Dowel Pin
Adam’s 12-valve Cummins is already updated with the “killer dowel pin” kit that prevents the aluminum timing cover’s 5/16-inch alignment pin (arrow) from vibrating out and possibly destroying the engine..
Photo 20/26   |   020 Cummins 6BT Rebuild Fleece Coolant Bypass
Another safety upgrade Eric is making during this rebuild is adding a Fleece Performance Engineering coolant bypass kit. Controlled by a secondary thermostat located in a CNC-machined housing, the bypass allows engine coolant to flow directly to the back cylinders.
Photo 21/26   |   021 Cummins 6BT Rebuild Oil Pump
The oil pump is a standard replacement part for all Dunks’ engine rebuilds. “It’s inexpensive and right out in the open,” Eric says.
Photo 22/26   |   022 Cummins 6BT Rebuild Oil Cooler
Another critical element of the rebuild is making sure the oil cooler is flushed and pressure-tested before reinstallation. This is a common failure item when miles and years start adding up, so make sure the parts that go back into the engine are trustworthy.
Photo 23/26   |   023 Cummins 6BT Rebuild Rear Main Seal
Eric says replacing the rear main seal is mandatory. Heat and age make it brittle and crack, as this one has done
Photo 24/26   |   024 Cummins 6BT Rebuild Install
Dunks Performance always has a steady flow of diesel engine repairs and rebuilds being added to the shop’s calendar. As Eric drops the rebuilt 12-valve into Adam’s ’97 Dodge Ram 3500 4x4, another customer’s Ram 2500 is waiting in the next bay to have the final touches applied to its rebuilt 24-vlave 5.9L.
Photo 25/26   |   025 Cummins 6BT Rebuild Banks TwinPak Intake
Eric replaces the stock Cummins single-plane intake manifold (laying on top of the engine) with Banks Power’s TwinRam manifold and up pipe. This intake upgrade ensures greater and more even airflow to the front and rear cylinders. Better airflow equals better fuel burn for more power and better mpg.
Photo 26/26   |   026 Cummins 6BT Rebuild Diamond Eye Exhaust Scr
Airflow is further enhanced by the 4-inch BD downpipe that plumbs right into a Diamond Eye Performance exhaust system, which is twice the diameter of the factory tubes.


Gale Banks Engineering
Azusa, CA 91702
BD Diesel Performance
Sumas, WA 98295
South Bend Clutch
Mishawaka, IN 46545
Diamond Eye Performance
Athena, OR 97813
Fleece Performance Engineering
North Salem, IN 46165
Hamilton Cams
Dunks Performance
Southworth, Inc.