The rotating assembly in the 2004.5–2006 6.6L LLY Duramax consists of the crankshaft, connecting rods, pistons, and related bearings—all components that convert combustion into rotational motion. The forged steel crankshaft is supported by main bearings and spins within the engine block, while the forged powder-metal connecting rods link the crank to the aluminum pistons. This assembly is known for its strength and durability at stock power levels, but the LLY’s rods are considered a weak point when pushed beyond 600–650 horsepower. The pistons have a slight bowl design optimized for diesel combustion, and the crankshaft features internal counterweights for balance. Proper lubrication and clearances are critical for longevity, making the rotating assembly a key focus area for performance upgrades, especially in high-power or race builds.