For those playing along at home, this issue finds us wrapping up our LB7 Duramax short-block build. Last time around, we dropped our trashed engine off with the skilled hands of L&R Engines in Santa Fe Springs, California. The block was disassembled, cleaned, and machined before heading to assembly. L&R’s resident Duramax expert, Frank, then installed the crankshaft, camshaft, and associated hardware. Our build continues as we prepare the rotating assembly for installation.
| While we thought it prudent to upgrade most parts, the factory rods were reused. LB7 connecting rods are known to be good for somewhere in the region of 700 rear-wheel horsepower, so with our goal being just slightly under that threshold, we made the decision to spare the expense of aftermarket rods and roll the dice on our stockers.
| What we did do, however, was upgrade from the factory connecting rod bolts to ARP units. ARP’s rod bolt kit features the company’s ARP2000 bolts, which are rated at 220,000 psi tensile strength and are reusable—unlike the factory torque-to-yield fasteners. Frank checked each rod and sized all the bolts prior to installation to ensure a proper fit and long life.
| For an added bit of insurance, we opted to replace the LB7’s pistons with upgraded units. Mahle Motorsports offers two levels of piston for the Duramax engine: cast and forged. With our output goals not being insane (by diesel performance standards, anyway), we chose the cast performance pistons over forged. Mahle’s cast performance pistons are machined from OE castings and retain the steel top ring insert. The bowls are de-lipped to help prevent erosion issues caused by high pressure, long duration, and advanced timing. Compression ratio is reduced slightly, from 17.5:1 to 16.8:1 on the standard pistons and 16.5:1 on units with machined valve pockets. Skirts are coated with a proprietary Grafal coating, which reduces drag and increases scuff resistance.
| Lb7 Duramax Engine Build Part 2 Pistons
| As with the main bearings, we also utilized Clevite H-Series bearings on the connecting rods. These performance bearings, originally designed for NASCAR racing, are among the best that can be purchased and are well suited to the high levels of stress a modified diesel engine creates.
| Frank carefully compressed the rings and knocked each piston into its assigned hole. Duramax pistons are directional, so care needs to be taken to ensure they land in the proper spot. Once the rings cleared the deck, Frank carefully guided each piston in, ensuring the rods didn’t knick or gouge the cylinder wall or crankshaft on their way in.
| With all the pistons installed, the ARP rods bolts were torqued to 95 ft-lb. ARP also includes instructions for using the stretch method to determine tightness, if you should choose to use this over a traditional torque wrench.
| Since the engine was open, we deemed it prudent to replace the oil pump as well, considering we had no knowledge of its history or origin. We used a factory replacement Melling M316 found for less than $200. The Duramax oil pump is located under the front cover and is geardriven off the crankshaft, so replacing one with the engine in the chassis can be quite difficult.
| With the oil pump in place, Frank could turn his attention to the oil pickup tube. The Duramax’s oil pickup is one of the most stout factory units we’ve encountered.
| As mentioned, the Duramax engine’s time and accessory drive is geardriven. While belts and chains can stretch and break, utilizing a geardrive ensures the engine won’t fall out of time and that critical accessories such as the oil pump, water pump, and high-pressure fuel pump will work flawlessly for (ideally) their entire life cycle.
| When Isuzu was designing the Duramax engine, we can only guess there was an engineer with an aversion to reusable gaskets, because most of the critical sealing surfaces use simple silicone. Included with our Clevite gasket set were two tubes of Victor Reinz Bead-n-Seal aluminum-silicone sealant. Frank used this wherever required, such as on the front cover.
| With the timing geardrive complete and silicone applied, the front cover was bolted into place.
| The front and rear main seals require a special tool set to install properly, which has caused issues for a lot of professional builders and shade-tree mechanics alike. Without the tool, leaks are almost a guarantee, even if a similar press is utilized.
| At this point, we just had to stop and admire the progress. What was once a nasty grease ball and then a pile of parts was starting to look like something substantial.
| The rear bellhousing adapter follows the same story as the front cover. Save for a pair of O-rings on the coolant passages, the cover seals to the block with a silicone bead.
| The rear main seal also uses a special tool for proper installation. You can see here the alignment pins that ensure the seal is perfectly centered on the rear of the crankshaft. It’s worth noting that L&R only uses factory GM rear main seals. On the hundreds of Duramax engines L&R has built over the years, the company has learned that nothing installs easier or seals better than the factory unit.
| After installing the rear main seal, Frank turned his attention to torquing the fasteners that secure the bellhousing adapter to the engine block.
| Duramax engines utilize a two-piece oil pan design. The upper oil pan, seen here, acts as a windage tray separating the crankshaft from the oil in the lower pan. Oil is allowed to drain off the rotating assembly into the pan, but dirty oil is restricted from splashing upward.
| The upper oil pan also has the unique job of connecting front and rear covers to the engine block. This creates what is essentially one cohesive structure between the three pieces. And, you guessed it, the pan seals to the block with silicone.
| With the upper oil pan in place, Frank turns his attention to the lower pan. The factory lower pan is a hideous stamped-steel piece, so naturally we replaced this with a cast-aluminum version from Pacific Performance Engineering. PPE’s lower oil pan increases capacity slightly, aids in cooling, and allows for a complete drain during oil changes, unlike the stock pan.
| While the engine was apart, we also chose to replace the factory water pump with an upgraded unit from Sinister Diesel. Factory Duramax water pumps are known to have their impeller and/or gear slip on the shaft since they are merely press-fit units. This issue is made worse when power and rpm is increased. Sinister fixes the issue by TIG-welding the impeller and drive gear to the shaft.
| Lb7 Duramax Engine Build Part 2 Water Pump
| It’s important to replace the water pump when the engine is apart for the simple fact that doing so requires removal of the harmonic balancer. While it’s certainly possible to perform the task while the engine is in the chassis, it becomes a fairly large project in itself.
| Since we’re not planning to spin the engine much faster than the factory limiter, and we balanced the entire rotating assembly, we chose to reuse the stock harmonic balancer. We did, however, replace the retaining bolt and washer with upgraded units from ARP.
| Duramax engines also utilize a two-piece ring gear and flexplate arrangement. Both are used to balance out the rotational forces of the engine, while the starter engages the ring gear and the flexplate connects the torque converter to the crankshaft.
| We made the call to upgrade our flexplate to BD Diesel Performance’s heavy-duty forged billet unit. As a direct bolt-in part, BD’s flexplate uses twice the material of the factory unit, is rated to handle up to 1,500 lb-ft of torque, and carries with it an SFI 29.3 rating. While solid flywheels exist, BD’s flexplate still allows for axial thrust, which prevents the issues that arise from using a solid piece in a non-dedicated race application. A black oxide coating prevents corrosion, and the whole thing is precision neutral balanced. Flexplate bolts need to be replaced whenever they are removed, so we took the opportunity to upgrade these to ARP as well.