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The Duramax L5P Goes Back Together

Numbers Game

John Lehenbauer
Aug 1, 2018
Photographers: John Lehenbauer
In the May 2017 issue of Diesel Power, in an article titled “Inside the Duramax L5P,” we visited Gale Banks Engineering in Azusa, California, and documented the complete dismantling of a straight-out-of-the-crate version of GM’s latest 6.6L powerplant. After the engine was completely taken apart, its individual components were compared side by side with the equivalent internal pieces of a Duramax LML. The comparison allowed us to see the innovations and changes GM integrated into its new diesel creation, and many of the features show there’s potential yet to be unlocked.
Not long after returning from our visit, we received a call from Gale Banks, who told us about his plan to put the same L5P back together. He explained that the reassembly process would include measuring tolerances and clearances of key pieces. Recording this data would also provide an accurate analysis of the engine that can be used to design such performance components as camshafts and pistons. It also provides insight into possible issues that may arise from modifying an L5P. Any time there is a chance to gain more understanding of what makes this new engine tick, count us in.
A few weeks after our phone conversation with Gale, we spent three days with Gale Banks Engineering’s lead engine builder, Mike Keegan, as he reassembled and measured the L5P’s critical internal components.
Photo 2/64   |   Mike Keegan begins the engine reassembly by measuring the different crankshaft journals. The main journal’s diameter is 3.1465 inches and the rod’s is 2.6771 inches. Every measurement Mike takes is recorded for future reference.
Photo 3/64   |   Duramax L5P Reassembly Mike Workbench
The bearing caps are installed on the block and torqued to specifications so the bore can be accurately measured.
Photo 7/64   |   Mike then removes the caps, installs the main bearings, and reattaches and torques the caps before measuring each individual bearing while it is in the block. By using the information he gathers about the crank, block, and bearings, and doing a little math, Mike calculates the main bearings have 0.0022 inch of clearance.
Photo 8/64   |   Duramax L5P Reassembly Engine Block Mike Micrometer
The camshaft’s journals (2.3995 inches), lobes, and cam bearings (installed in the block) are analyzed next. After recording the measurements, Mike smears the cam bearings and shaft with assembly lube before installing the cam in the block.
Assembly lube is applied to the crankshaft’s bearings and journals before the crank is set into the block. Bearing-cap main bolts are torque-to-yield (the fastener is designed to yield/stretch when torqued), which causes it to deform and become permanently elongated, so new bolts must be used for final assembly.
Photo 16/64   |   The rear main bearing is the only one that is caged. Thrust washers are installed with the rear main-bearing cap.
Silicone is applied to the original side bearing cap bolts before they are installed. Once they are installed, all the cap bolts are torqued to specification. After the bolts are secured, Mike checks the crank thrust clearance.
Photo 20/64   |   Next, the oil squirters are installed and torqued.
Photo 21/64   |   The timing gears are installed on the crank and camshaft with the timing marks aligned. The cam’s timing gear features a spring for damping shock. To install the gear, the spring is preloaded and tension is held with a set screw. The screw is removed once the timing gear is aligned and bolted into position with the crank gear.
Photo 22/64   |   Lifters are installed in the guides before the assembly is mounted in the block.
Mike measures a piston’s wristpin bore, wristpin, and rod bearings before mating the pistons to the connecting rods. This provides the measurements used to determine the clearances between components. Our L5P’s wristpin-to-piston clearance is 0.0008 inch.
Photo 26/64   |   Ring gaps are checked inside the cylinder before the rings are installed on the pistons. The first ring has 0.014 inch of gap while the second has 0.019 inch. Once installed, the rings (and wipers) are checked to ensure they are clocked correctly.
Photo 27/64   |   Duramax L5P Reassembly Vise Piston Rod Ring Install
All the pistons and cylinders are measured to check tolerances. The piston diameter is 4.0521 inches and cylinder bores are 4.0551 inches, which creates a clearance of 0.003 inches. The bores have a straightness taper of 0.0003 inches and are 0.0002 inches out of round. Rod bearings are coated in assembly lube before the pistons and rods are installed.
Photo 32/64   |   After all the rods are installed on the crankshaft and torqued, the gaps between each rod are checked.
Photo 33/64   |   Mike uses a special dial indicator to check the deck height of the piston and verify the correct gasket thickness. These measurements guarantee optimal combustion and compression ratio (16.8:1).
Photo 34/64   |   An aluminum spacer is used to measure the static position (open and closed) of the intake and exhaust valves. This data provides the correct spring length, which helps determine the spring pressure with the valves open and shut.
Photo 35/64   |   Duramax L5P Reassembly Cylinder Head Dial Indicator Up
Photo 36/64   |   Mike determines the factory camshaft has an intake lobe with 0.389 inch of lift and exhaust lobe of 0.393 inch of lift. The L5P also uses an intake rocker-arm with a 1.39 ratio and exhaust arm with a 1.69 ratio, which increases the camshaft’s total lift to 0.540 inch (intake) and 0.664 inch (exhaust). He measures the distance between the valvespring retainer and the seal (confirming spring height) to know exactly how much more lift and duration can be used on a camshaft before any retainer-to-seal contact would occur. It should be noted that L5P cylinder heads use a new type of valve seal that is held in place with the valvespring, which eliminates the chance of the seal becoming dislodged or moving.
Photo 37/64   |   With the valve removed, Longacre’s Digital Spring Compressor is used to compress the valvespring to the height that was measured with the valve installed and then to press the spring completely to check for binding. Finding the distance at which the spring binds determines the amount of lift that spring can handle.
Photo 38/64   |   Mike installs a degree wheel on the crankshaft and a pointer on the block to find top dead center on the Number One cylinder. He uses a dial indicator to verify exact TDC.
Photo 39/64   |   With the degree wheel installed and TDC set, the cylinder head is installed with four bolts and a head gasket. Four of the valves (two intake and two exhaust) in the head have lighter “checker” springs installed. Mike rotates the crank so the valve can be opened and sets the dial indicator to measure the point at which the valve begins to come in contact with the piston. He notes the crank’s position in degrees versus the depth of the valve in the cylinder. The same process is used to determine at what degree the piston-to-valve interference ends. All four valves are measured.
Photo 40/64   |   Duramax L5P Reassembly Dial Indicator Cylinder Head
Photo 41/64   |   After checking piston-to-valve interference, Mike removes the head and reinstalls the proper valvesprings. He then assembles the top end of the engine with new head gaskets and bolts. The head bolts on an L5P are also torque-to-yield, so new head bolts are a must. With the heads torqued, the pushrods, valve cover gaskets, and rocker arm assemblies are installed.
Photo 42/64   |   Duramax L5P Reassembly Rocker Install
Photo 43/64   |   Once the valve covers are in place, the fuel injectors and lines are mounted.
Mike begins assembling the front of the L5P, installing the oil-pump drive gear, oil pump, high-pressure fuel pump, and timing cover.
Photo 47/64   |   A special installation tool is needed for the front main seal.
Photo 48/64   |   Mike hoists the L5P off the engine stand to install the flywheel housing on the back of the block. With housing in place, the rear main seal is installed using the proper tool.
Photo 49/64   |   Duramax L5P Reassembly Back Engine Flywheel Cover
Photo 50/64   |   With the engine back on the stand, the water pump is installed.
Photo 51/64   |   Mike installs the fuel-feed lines and return lines.
Photo 52/64   |   The L5P’s large oil cooler and filter adapter are installed with all new gaskets.
Photo 57/64   |   The engine assembly is finished off with installation of the wiring harness.
Photo 58/64   |   Engine complete on stand.

What Are the Limits of a Stock 6.6L Duramax L5P Engine?

Tearing an engine apart and putting it back together can yield a lot of information about that powerplant, including how well or how poorly it is constructed. However, disassembly and rebuilding does not provide all the facts about what the engine can do. The only way to truly understand everything is to test it. And the best place to test an oil-burner is in the controlled environment of a dyno cell.

Shortly after Gale Banks Engineering’s lead engine builder Mike Keegan finished reassembling the 6.6L Duramax L5P engine, the powerplant was mounted on the dyno (minus the EGR and catalytic converter, in order to see how the engine performs without those restrictions), ready to be put through its paces.

One problem with the engine not having an EGR is that all the exhaust gases go directly into the turbocharger. The excess exhaust volume is more than the turbo is designed to support, which hinders its ability and efficiency.

On the dyno, a Banks ECU is used to control engines that are being tested, making easy fuel and timing adjustments possible for our L5P test. Sensors were installed to monitor every pressure, temperature, density, and bit of data that can be analyzed. All the information was tied to two prototype Banks Power iDash gauges that act as data loggers.

For the first test, which we used as a baseline, the engine was run at 2,800 rpm. It produced 450 hp and 844 lb-ft of torque (peak torque is at 1,600 rpm) and put out lots of vital ancillary information. Additional tests were then performed, with minor adjustments made to timing, fuel, and the position of the turbo’s vanes in order to determine the engine’s maximum potential. With the turbo vanes wide open, fuel delivery increased (to the upper limit of the stock system), and timing set to a sweet spot (advanced until an increase in performance was seen), our L5P made 540 hp and 915 lb-ft of torque at 3,100 rpm—the limit for the turbocharger (it got too hot due to an overabundance of exhaust-drive pressure), as well as the fuel system.

The dyno gives us an abundance of information about the stock L5P’s performance potential and its limits. Capturing this type of data can be a huge benefit to engine builders and aftermarket-parts manufacturers who are working to resolve the engine’s shortcomings and push its performance limits farther.
A look inside Banks Power Dyno Cell 2 and the 6.6L Duramax L5P engine that is ready to run.
Photo 62/64   |   Gale Banks provided us with some insight on how the engine dyno works.
Photo 63/64   |   Aaron Sandstrom mans the controls, while Gale Banks monitors instruments during the L5P’s pulls on the dyno.
Photo 64/64   |   Duramax L5P Reassembly Dyno Control Room Looking Into Dyno Cell


Gale Banks Engineering
Azusa, CA 91702