D&J Precision Machine built its reputation in the diesel world around serious Cummins engines, precision machining, and high-horsepower applications. Now the Cambridge, Ohio, engine builder is taking that experience into a different corner of the diesel market with a new line of remanufactured 6.6-liter LML Duramax long blocks.
The new program launches with two engines aimed at 2011-2016 Chevrolet Silverado and GMC Sierra 2500HD and 3500HD trucks: the Precision Plus and the Essentials. While the two packages differ significantly in how complete the engine is and in several key upgrades, both begin with the same basic philosophy. D&J completely disassembles, cleans, inspects, machines, and rebuilds each engine in-house rather than treating the replacement as a simple stock-spec refresh.
“LML owners depend on these trucks for work, towing and everyday driving, and when an engine needs replacing, they want confidence in what’s going back under the hood,” said D&J Precision Machine CEO Drew Pumphrey. “We’ve spent years developing and refining our Cummins engine programs, and we’re bringing that same experience and attention to detail to the Duramax platform.”
Starting With The Block
Both D&J LML packages start with a fully remanufactured long block. The engine is completely torn down before the block receives D&J’s machining process. According to the company, that includes CNC blueprinting, boring, honing, and surfacing the deck to establish proper cylinder geometry and piston fit. The crankshaft is also checked for straightness and dimensional accuracy and repaired as necessary.
Rather than reusing the original piston assemblies, D&J installs new OEM-spec Tier 1 pistons and rings. The crankshaft and camshaft are also keyed. This as a way of reducing the possibility of unwanted gear movement that can alter timing or lead to related component damage.
New bearings and thrust washers restore the internal clearances of the rotating assembly, while new lifters, valve springs, and freeze plugs are installed during the remanufacturing process.
This is not an oversized aftermarket competition engine or a race-oriented redesign of the Duramax architecture. Instead, the initial D&J LML program is focused on creating replacement engines for trucks expected to return to daily driving, work, and towing duty.
Reworking The LML Cylinder Heads
The cylinder heads receive their own rebuilding process rather than simply being cleaned and bolted back onto the block. D&J inspects and resurfaces the heads, recuts the valve seats, and installs new valves.
One notable change is the use of an upgraded L5P-style top-hat valve stem seal. D&J says the newer seal design is intended to improve valve sealing and reduce the potential for valve-seal-related problems over the life of the engine.
The Essentials engine receives Tier 1 head gaskets, while Precision Plus takes the cylinder sealing package another step with Tier 1 multi-layer-steel head gaskets and ARP head studs.
That combination is specifically aimed at one of the issues D&J identified when developing its LML program: cylinder-head sealing. The additional clamping force provided by the studs is intended to help maintain gasket sealing under demanding operating conditions rather than reinstalling the engine with a factory-style head-bolt arrangement.
Precision Plus Goes Deeper
Where the two engines really begin to separate is with the additional systems and components included with Precision Plus.
Along with the upgraded head-fastener package, Precision Plus receives an L5P oil cooler. D&J says the newer cooler provides increased oil-cooling capacity, helping control oil temperature and reduce the conditions associated with piston cracking and related piston failures.
The oil pump is pinned as well. The modification provides positive mechanical retention of the pump drive to help prevent rotation or slippage and maintain consistent oil pressure.
For a technically minded Duramax owner, the combination is significant because D&J is addressing several different systems rather than concentrating exclusively on the short-block assembly. Cylinder sealing, oil temperature, oil-pump retention, timing-component retention, valvetrain condition, and piston-and-ring fit are all dealt with during the build.
Precision Plus is also much closer to a complete drop-in assembly.
D&J supplies the engine with rocker assemblies, pushrods, valve bridges, rocker boxes, valve covers, and the intake manifold. The rotating-assembly package also includes the harmonic balancer, flywheel, flex plate, flex-plate washer, and new mounting hardware.
Including those components serves two purposes. It reduces the number of parts that must be removed from the failed engine and transferred to the replacement, and it gives D&J more control over what components become part of the completed installation.
That difference shows up in the estimated labor time. D&J lists approximately 19 hours to install the Precision Plus engine.
Essentials Takes A More Traditional Long-Block Approach
The Essentials package is designed around the same basic machining and rebuilding process but leaves more of the final assembly to the installer.
It uses the precision-machined block, OEM-spec Tier 1 pistons and rings, remanufactured cylinder heads, new valves, L5P-style top-hat valve stem seals, keyed crankshaft and camshaft, new internal wear components, and D&J’s in-house testing process.
Where it differs is in the amount of equipment supplied with the engine and some of the upgrades included in the Precision Plus package. The Essentials long block is intended to be finished during installation using applicable components transferred from the original engine. D&J estimates the job at approximately 25 labor hours, compared with 19 hours for Precision Plus.
There’s also a substantial price difference.
Essentials, part number DJPLB100116, carries a U.S. price of $9,499.99. Precision Plus, part number DJPLB100111, is listed at $13,499.99. Both carry a $3,000 core charge. Canadian pricing is listed at $13,299.99 CAD for Essentials and $18,949.99 CAD for Precision Plus.
In other words, Essentials gives a shop or truck owner the D&J-machined foundation while allowing more of the original engine’s reusable hardware to carry over. Precision Plus adds several mechanical upgrades and considerably more of the hardware necessary to complete the installation.
Testing Before It Leaves Cambridge
Machining tolerances and component selection only matter if the completed engine operates as intended, so D&J has incorporated end-of-line testing into the LML program.
Every engine is checked in-house using the company’s RMC ETS-100 engine-testing equipment. D&J describes the process as a controlled test sequence intended to verify cylinder compression and cooling-system integrity before shipment, oil-pump pressure and volume are also checked.
That kind of testing provides an opportunity to identify assembly, sealing, compression, or oiling problems before the long block is installed in a truck, where diagnosing the same issue would involve significantly more labor and expense.
Built For 2011-2016 LML Trucks
Both engines are intended specifically for the 6.6-liter LML Duramax used in 2011-2016 Chevrolet Silverado 2500HD and 3500HD models and their GMC Sierra 2500HD and 3500HD counterparts.
D&J has also identified several complementary components for the platform, including its listed Screamer LML turbo, stock replacement LML turbo, Duramax exhaust-manifold kit, remanufactured LML injectors, CP3 conversion kit, and Duramax flexplate.
Both long blocks are backed by a 24-month/100,000-mile parts warranty and 24 months of labor coverage, subject to D&J’s warranty terms and conditions.
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