QSB6.7 Marine Long Block Workhorse (425-550 HP) Diesel Crate Engine Choate Performance (Copy)

QSB6.7 Marine Long Block Workhorse Engine The QSB6.7 Marine Engine is designed for maximum-performance vessels—such as high-output sportfishers, motor yachts, and rapid-response patrol boats operating frequently at high RPM and wide-open throttle (WOT), where engine failure on open water is completely unacceptable. Upgrades Over the Daily Driver: O-Ringed Heads Coated and Fly Cut Pistons Stage 2 Cam Chromoly Pushrods Key Features and Fixes High-Output Performance: Rated for 425-550 HP for maximum performance vessels. Vibration Mitigation: A fully balanced rotating assembly ensures your vessel runs quiet and smooth, protecting your transmission and running gear. Enhanced Valve Integrity: Features all-new, upgraded exhaust valves that eliminate high-heat separation, preventing catastrophic engine failure at sea. Corrosion Resistance: Billet freeze plugs are installed to eliminate the "rot-out" common with standard brass or steel plugs in marine environments. Machining Process: At Choate Engineering Performance, we don’t just "overhaul" marine engines, we remanufacture them to surpass original factory specifications. Our QSB6.7 marine engines undergo rigorous CNC blueprinting to correct OEM flaws, ensuring the ultimate reliability required for offshore and coastal applications. Engine Block Machining: Each of our engine blocks are CNC blueprint machined using state-of-the-art CNC machines. This process ensures perfect dimensions, precise tolerances, and optimal alignment. This starts with decking the surface of the block to achieve the necessary flatness and smoothness (Ra 30 or better) required for flawless sealing with MLS head gaskets. The cylinders are then diamond honed to an extremely tight tolerance to match the piston diameter (within the nearest 0.0001 inch). Following honing, the main bearing bores are line honed to establish a true, straight centerline for the crankshaft. Finally, the cylinder bores are bored to a true 90 degree angle from the crankshaft centerline. Cylinder Head Machining: Our cylinder heads are fully machined and enhanced in-house to improve airflow and reliability. Each head is first magnafluxed and pressure tested to ensure they are free of any cracks or leaks. The surface is then precision decked to an extremely smooth finish, guaranteeing the necessary flatness for a perfect seal with MLS head gaskets. Internally, the valve seats are machined to optimize airflow and prevent common failures, and the entire valve train geometry is blueprinted to specific tolerances to reduce lifter preload and prolong component life. Rotational Assembly Balancing: The balancing of the rotational assembly is crucial for eliminating vibration and maximizing engine longevity. This precision work involves checking and correcting the balance of the crankshaft, connecting rods, and pistons. The crankshaft is thoroughly checked for run-out and inspected for fatigue before being polished and ground to strict concentricity tolerances (0.0005 or less) to ensure the new bearings receive the best possible surface. Rods are inspected and conditioned, and all bearing clearances checked to ensure proper fitment with the new bearings. Each of the pistons, rings, and pin retainers are meticulously weight matched (to a tolerance of 2 grams or less) prior to crank balancing. Then the entire assembly is dynamically balanced on specialized equipment. This ensures that the engine runs smoothly, minimizing stress on the bearings, and extends the overall life of the components. Components and Parts: Engine Core Components Cylinder Block Crankshaft Steel Connecting Rods Stage 2 Camshaft Coated and Flycut Pistons O-Ringed Cylinder Head Chromoly Pushrods New Main Bearings New Rod Bearings New Cam Bearings Main Bolts Head Studs Rockers Billet Freeze Plugs New Oil Pump Upper Oil Pan Lower Oil Pan Gaskets and Seals New Head Gaskets Rear Main Seal Front Gear Housing Cylinder Head Components New Valve Guides New Socket Plug New Oversized Valve Seats New Threaded Plugs Marine-Grade Confidence: 2 Year / 2,000 Hour Warranty When you’re out on the water, reliability isn’t just a luxury, it’s a necessity. At Choate, we stand behind the precision engineering of our QSB6.7 Marine Engines with a comprehensive 2-Year / 2,000-Hour Warranty. We understand that marine environments are among the most demanding on earth. From high-idle trolling to wide-open throttle transitions, our warranty is designed to give you total peace of mind while you navigate. Whether you are a commercial operator or a recreational enthusiast, we ensure your investment is protected against defects in materials and workmanship.