6.6L Duramax LB7 Short-Block Rebuild: Part 1
6.6L Duramax LB7 short-block rebuild: Part 1
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.
The ’02 Chevrolet Silverado 2500HD owned by Monica Gonderman (yes, the Truck Trend Network’s daily news editor) came with a 6.6L Duramax LB7 engine that had succumbed to a blown cylinder head gasket, burned piston, and munched head by way of poor tuning and a throttle-happy previous owner. A botched rebuild landed the truck in Monica’s driveway for little more than a song. While she could have quickly slammed the engine back together with an eBay piston and replacement head, the Gondermans decided that with more than 200,000 miles on the odometer and future power goals of more than double the stock output, they will be better served to tear the engine down and do it right.
For this, Monica 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 first disassembles the dirty short-block, then gives the core a much-needed wash in the hot tank before Magnafluxing it to check for hairline cracks and irregularities that could pose issues down the road.
After cleaning and inspection, the cylinders are bored and honed, the main bearing bores are line-honed, and finally the deck surface is milled. This all ensures the block is perfectly square and ready to run for another quarter-million miles. After installing new freeze plugs and a quick coat of paint, the block is ready for reassembly, which we’ll review in a future report.
The engine was taken to the Duramax experts at L&R Engines in Santa Fe Springs, California, where it was stripped down and received the full prep treatment (cleaning, machining, and such).
Frank, an L&R engine specialist, has been building engines nearly his entire life. Before starting the rebuild, he gives the block a good cleaning. Brake cleaner and a rag work wonders for removing any remaining machining oil and residue.
Duramax engines use oil squirters to provide cooling for the pistons . 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.
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 camshaft receives a hot bath before being lubed for installation. The stock cam is reused because it works exceedingly well for the power level
(650 hp) Monica and Jason are shooting for, but also because not many aftermarket replacements exist.
Interestingly, L&R reuses the factory cam bearings. Building one to two Duramax engines a week, Derek says they have yet to come across a failed factory bearing. He believes the stock hardware is made better and stronger than pieces that are available in the aftermarket.
One of the most common failure points on Duramax engines is the cam-gear retention pin. This tiny dowel pin is fully responsible for keeping the camshaft timed to the engine’s rotation. Surprisingly, we found the pin had oblonged its mounting hole in the camshaft, and it literally fell out. The rebuilt engine would have been moments away from catastrophic failure had this problem not been discovered.
The solution to the dowel pin issue is to machine 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 into 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 turns his attention to preparing to install the crankshaft. The Clevite H-Series main bearings being used 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 cranks are known to break near the first counterweight. This often happens when people increase power and rpm but don’t properly balance the rotating assembly. The crankshafts also suffer from the same issue as the camshaft’s dowel pins and are often keyed as well.
In an effort to increase bottom-end strength, the stock main-bearing bolts are ditched in favor of ARP studs. Each stud is threaded in by hand before being cinched down with an Allen head socket to ensure it is installed to the proper depth.
With the studs installed, Frank carefully lowers each of the main-bearing caps into place. These caps need to be installed in the same position and same orientation they were removed from, 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 torques 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 retaining bolts that run horizontally through the block on either side of the main-bearing caps. They are included with the stud kit and torqued to specification after the studs are secured.
With the crankshaft installed, Frank turns his attention back to the camshaft by bolting the retaining plate into place. This can be done at any time, but it actually coincides with the next step.
Affixing the camshaft timing gear and aligning it with the crankshaft is the finishing task for cam and crank installation. Duramax engines utilize a gear-driven timing system instead of belt or chain arrangements, and the camshaft is driven directly by the crankshaft.
Upon finding a burned piston and a poor attempt at a repair and reassembly, Monica and Jason Gonderman made the tough decision that the 6.6L Duramax LB7 engine in Monica’s ’02 Chevrolet Silverado 2500HD needs to come out. And because the truck has more than 200,000 miles on it (the actual mileage is still a mystery) and the plan is to achieve a power figure that will push the limits of the stock internals, a full rebuild is in order.