Diesel engines are designed to be in service for a very long time. Because of this, it’s no surprise that we often find prime examples running flawlessly with mileage well into six digits. However, with the rise of the diesel performance industry has also come more frequent rebuilds. One camp rebuilds due to damage, while the other does so to increase performance. We fall into both camps.
Our ’02 LB7 Duramax succumbed to a blown head gasket, burned piston, and munched head by way of poor tuning and a throttle-happy previous owner. A botched rebuild landed it in our driveway for little more than a song. While we could have quickly slammed the engine back together with an eBay piston and replacement head, we finally came to our senses and decided that with more than 200,000 miles on the clock and future power goals of more than double factory, we would be better served to tear the engine down and do it right.
For this, we turned to the skilled hands at L&R Engines in Santa Fe Springs, California. L&R is a small family-run shop that was founded in 1976 in the garage of Larkin Ranney and his wife Robbie. Now, 41 years later, the business is still a family affair, with sons Derek and Brent joining their parents for the daily grind of operating a highly successful engine building enterprise. L&R can handle anything from classic flatheads to large marine diesels and has a particular specialty in building performance Duramax engines.
L&R set to work by quickly disassembling our dirty short-block. The block was then given a much-needed wash in the hot tank before being Magnafluxed to check for hairline cracks and irregularities that could pose issues down the road. Next, the cylinders were bored and honed, the mains were line honed, and finally the head-mounting surface was decked. This all ensured the block was perfectly square and ready to run for another quarter-million miles. After installing new freeze plugs and a quick coat of paint, the block was ready for reassembly.
| Upon finding a burned piston and a really poorly made attempt at a repair and reassembly, we made the tough decision that the engine needed to come out. And because we know the truck has more than 200,000 miles on it (the actual mileage is still a mystery) and we’re shooting for a power figure that will push the limits of the factory internals, we decided a full rebuild was in order.
| We took our LB7 to the Duramax experts at L&R Engines in Santa Fe Springs, California, where it was stripped down and received the full treatment. We caught up with the build when it was ready for assembly—after all the dirty machine work was completed.
| Before beginning, Frank, who has been building engines nearly his entire life, gave the block a good cleaning. Brake cleaner and a rag work wonders for removing any remaining machining oil and residue.
| Duramax engines have used oil squirters to provide cooling for the pistons since day one. These small tubes are affixed to an oil galley with banjo bolts and provide a concentrated blast of oil directly to the bottom of the piston.
| Interestingly, L&R reuses the factory cam bearings. With the frequency of building one to two Duramax engines a week, they told us they have yet to come across a failed factory bearing. They are simply made better and stronger than what’s available in the aftermarket.
| Cleanliness is of utmost importance when building any engine. Frank takes the time to clean every part—even down to the bolts—before reassembly. Here the factory camshaft receives a hot bath before being lubed up for installation. The factory camshaft was reused because it works exceedingly well for the power level we desire and the simple fact that not many aftermarket replacements exist.
| One of the most common failure points on Duramax engines is the cam gear retention pin. This tiny dowel pin is all that is responsible for keeping the camshaft timed to the engine’s rotation. Surprisingly, on our engine that had nothing more than a tuner on it in its previous life, we found that the pin had wallowed out its mounting hole in the camshaft and fell out in our hand. This engine was moments away from catastrophic failure had we not found this.
| LB7 Duramax Engine Build Pin
| The solution to the dowel pin issue is to machine out a pocket in the camshaft and install a 5mm woodruff key. Commonly referred to as “keying the cam,” the woodruff key allows the cam timing gear to attach with no modification and will stay in place even at the most extreme power levels.
| Back at the wash tank, Frank prepares the lifters for installation. The rollers on the lifters are especially susceptible to contamination, so it’s important they go back in clean.
| A heavy coat of assembly lube is applied to each lifter. This thick lubricant helps ensure no damage is caused to the lifter or camshaft upon the initial start-up, before the oiling system reaches full pressure.
| Inserting the lifters back in the engine is as much an art as it is a science. Each pair is held in place with a guide plate and keeper assembly and needs to be perfectly aligned for the setup to attach properly.
| With the camshaft and lifters in place, Frank turned his attention to the preparations needed before installing the crankshaft. We opted for Clevite H-Series main bearings. These high-performance bearings feature enlarged chamfers at the sides for greater crank-fillet clearance and are produced without flash plating for better sealing.
| Laying the crankshaft is a two-person job due to its size and weight. The crank needs to be lowered into the block as straight and level as possible to prevent any dings or scratches to the polished bearing surfaces.
| Another Duramax engine failure point is at the crankshaft. While it’s extremely rare, Duramax crankshafts have been known to break near the first counterweight. This often happens when people add more power and rpm but don’t properly balance the rotating assembly. Duramax crankshafts also suffer from the same issue as the camshaft with the dowel pins and are often keyed as well.
| In an effort to increase bottom end strength, we ditched the factory main bearing bolts in favor of ARP studs. Each stud was threaded in by hand before being cinched down with an Allen head socket to ensure it was installed to the proper depth.
| With the ARP studs installed, Frank carefully lowered each of the main bearing caps into place. These caps need to be installed in the same position and same orientation from which they were removed, and care needs to be taken not to damage the stud threads while lowering the cap into place.
| After applying copious amounts of ARP’s Ultra Torque lubricant, Frank proceeded to torque the main cap studs to 175 ft-lb and the cross bolts to 90 ft-lb in the proper sequence.
| In addition to the vertically oriented studs, Duramax engines also use a horizontal bolt that runs through the block on either side of the main bearing caps to aid in retention. ARP provided these with the stud kit, and they were torqued to spec after the studs.
| With the crankshaft installed, Frank turned his attention back to the camshaft by bolting the retaining plate into place. This could have been done at any time, but Frank held off, coinciding with the next step.
| Finishing off the camshaft and crankshaft installation was affixing the camshaft timing gear and aligning it with the crankshaft. Duramax engines utilize a gear-driven timing system instead of inferior belt or chain arrangements, and the camshaft is driven directly by the crankshaft.