2007.5-2010 Chevy Duramax LMM Engine Components

Inside the LMM long block

The LMM is a Duramax LBZ long block with the block casting reinforced, better main bearing material, thicker connecting rod I-sections and a larger piston pin bore. It is a gray iron deep-skirt block with cast aluminum heads, a nitrided forged crankshaft and fracture-split forged rods, 4.055 in bore by 3.897 in stroke, 16.8:1 compression. The valvetrain is cam-in-block overhead-valve with hydraulic roller lifters and four valves per cylinder. Fuel enters through six-hole nozzles on a Bosch common rail system that peaks at 26,000 psi, and that nozzle pattern is the reason the pistons matter as much as they do. When you are deciding whether a used engine is worth freshening, 300 psi is the minimum compression figure for these.

What fails and why

Pistons are the LMM's power limiter, and the number is around 600 hp. The six-hole pattern aims opposed fuel streams above the wrist pin and builds a hot spot there, so cracked pistons show up on trucks with aggressive timing, extra fuel or long pulls at high exhaust temperature. The warning is sudden damage under load and crankcase pressure, not a slow decline. Head gaskets are a different story: the riveted gasket used from late 2006 through 2010 is the best factory design and rarely lets go by itself, but an overheat will finish it, and the signs are coolant loss, a pressurized cooling system and white sweet smoke. Fuel dilution of the oil from particulate filter regeneration runs in the background on every one of these engines, since raw fuel washes down the cylinder walls into the crankcase and above five percent by volume the oil has lost the lubricity the bearings are counting on. There is no documented LMM-specific valvetrain failure pattern, so rocker and spring parts here are build items rather than the fix for a known defect.

Stock replacement vs. upgrade

A gasket-and-seal refresh on a stock truck is a replace-in-kind job: match the original gasket style, choose the engine gasket set that covers what you are actually removing, and reseal the timing cover and rear main while access is open. The one upgrade we recommend without hesitation on a truck that tows or is tuned is ARP head studs with the riveted-style late-2006-2010 gasket; the A through D grades only describe thickness, so the grade is a measurement, not a quality ladder. Past that, main studs, rod bolts, crankshaft dowel pin kits and valve spring sets are power-build hardware that goes in when the pistons do. Stock-replacement CP3 pumps and 10, 12 and 14 mm stroker CP3s are both cataloged for the LMM, so pick fueling and pistons together rather than in sequence. Whatever you build, keeping exhaust temperature down and staying off stacked tunes is what keeps the pistons in one piece.

What we carry

Mahle covers sealing: lower engine gasket sets, engine gasket sets without head gaskets, timing cover gasket sets and seals, and rear main crankshaft seals. Merchant Automotive lists full engine gasket sets with or without head gaskets and with or without bolts, plus pushrods, oil cooler installation and seal kits, high performance motor mounts, a deluxe glow plug replacement kit and glow plug nuts. XDP brings X220 head and main stud kits, connecting rod bolt kits, crankshaft dowel pin kits, HD rocker arm shafts and billet valve bridges, street performance pushrods, valve springs and retainers, stock and performance harmonic balancers, and camshaft and crankshaft position sensors. Pistons are listed in this group as well. ARP and Gator Fasteners add fastener kits, PPE the silicone engine mount bushings, oil filler cap and oil filtration hardware, ACDelco the 9G glow plug and Dorman an engine oil cooler. Parts from BD Diesel, Wehrli Custom Fabrication and Fleece Performance Engineering also appear in this group.

Fitment notes

Buy by engine code. Internal parts for these engines are routinely cataloged 2001-2010, 2006-2010 or 2006-2016, which spans LB7, LLY, LBZ, LMM and LML, so the year filter alone will hand you parts that do not belong in your truck, and glow plugs are the classic example. Watch the 2007 overlap, since a 2007 Silverado HD Classic is the earlier body with the LBZ. The engine oil cooler on these trucks is built into the driver-side radiator tank, so confirm which cooler assembly and seal kit your truck actually uses before ordering. Head gasket grade is measured, not guessed, and gaskets are sold by side as well as grade. Nothing here carries forward to a 2011 LML, which changed to a CP4 pump and added DEF. When a listing range is broad, use the fitment checker on the product page or call us with the VIN.

Frequently asked questions

How much power will stock LMM pistons hold?

Figure around 600 hp as the practical ceiling. The six-hole injector spray pattern concentrates heat above the wrist pin, so what cracks them is aggressive timing, over-fueling and sustained high exhaust temperature under load. If the build target is past that, the pistons come out and the fueling plan goes in at the same time rather than later.

Which engine gasket set should I order?

Order by what you are taking apart. The sets come with head gaskets or without, and with bolts or without, and there are separate lower engine gasket sets for bottom-end work. Head gaskets are also sold individually by thickness grade and by side, so if the heads are coming off, measure and order the grade your engine calls for instead of assuming.

Are head studs worth it on a truck that only tows occasionally?

If the heads are already off, yes. ARP studs with the riveted-style late-2006-2010 gasket is the spec we build to for towing and tuned trucks, and the labor to do it later is the same labor you are paying for now. On a sealed stock engine that has never overheated, there is no reason to go looking for the job.

Not sure what fits? Call the shop at the number in the header, or use the fitment checker on any product page. We install everything we sell.