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Cummins QSB6.7 Specifications
| Engine Model: Cummins QSB6.7 |
| Engine Type: 4-cycle inline 6-cylinder common-rail direct injection liquid-cooled diesel |
| Total Displacement: 409 cu.in (6.7 L) |
| Rated Engine Power: 160-300 Hp (119-224 kW) at 2200 rpm |
| Aspiration Type: Turbocharged |
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| General Technical Data |
The Cummins QSB6.7 is a high-performance, electronically controlled, turbocharged and aftercooled, inline six-cylinder diesel engine designed for modern agricultural machinery, construction equipment, forestry machines, material-handling equipment, generator sets, mining support vehicles, and multiple off-highway industrial platforms. As a member of the Cummins Quantum System (QS) engine family, the QSB6.7 combines advanced electronic management, high-pressure common-rail injection, improved combustion efficiency, reduced emissions, and excellent power density.
It complies with global emissions standards
including Tier 3, Tier 4 Interim, Tier 4 Final, Stage IIIA, Stage IIIB,
Stage IV, and Stage V depending on version. The engine is renowned for
its smooth operation, high torque output, fuel economy, long overhaul
life, and flexible configuration options. Its compact, modular structure
and robust architecture support installation in confined engine
compartments while maintaining superior serviceability.
The QSB6.7 is a four-stroke, inline six-cylinder diesel engine with a
displacement of approximately 6.7 liters (409 cubic inches). Bore is
typically 107 mm (4.21 inches), and stroke measures about 124 mm (4.88
inches), producing a long-stroke design optimized for low-speed torque
and high power density. Compression ratio varies with emissions tier but
commonly falls between 16.5:1 and 17.3:1.
Power output ranges broadly from 119 to 224 kW
(160–300 horsepower) at around 2200 rpm depending on configuration. Peak
torque is generally between 700 and 1100 Nm (516–811 lb-ft), typically
available around 1400–1600 rpm. Idle speed is usually set near 750 ± 50
rpm. The electronically controlled turbocharging system supports rapid
transient response, strong altitude compensation, and smooth load
transitions.
The QSB6.7 cylinder block is cast from high-strength iron with deep
reinforcement structures designed to withstand the increased firing
pressures associated with modern high-power, low-emissions diesel
engines. Precision machining ensures optimal alignment of crankshaft,
camshaft, and cylinder bores. The forged-steel crankshaft rides on seven
main bearings engineered for long service life and minimal torsional
vibration.
Cast-in coolant jackets and structural ribs
enhance heat distribution and block rigidity. Internally machined oil
galleries deliver lubrication to the main bearings, connecting rod
bearings, camshaft bearings, piston cooling jets, and other load-bearing
surfaces. Threaded bosses and accessory mounting pads accommodate a wide
range of hydraulic pumps, alternators, A/C compressors, PTO drives, and
industrial attachments.
The cast-iron cylinder head of the QSB6.7 contains direct-injection
combustion chambers optimized for clean combustion and strong torque
output. Each cylinder uses four valves–two intake and two
exhaust–improving airflow and enabling efficient breathing at high rpm
while enhancing low-speed torque. Valve actuation is via pushrods and
rocker arms driven by a gear- or belt-driven camshaft depending on
configuration. Some emissions-tier variants include hydraulic lash
adjusters to minimize maintenance.
Hardened valve seats, high-strength valve guides, and reinforced bridge designs ensure durability under continuous high-temperature load. The combustion geometry, designed with advanced swirl and tumble characteristics, supports efficient fuel-air mixing, helping reduce soot formation and fuel consumption. Coolant passages are integrated to manage temperature distribution across the head.
| Fuel System |
The QSB6.7 employs a high-pressure common-rail fuel system delivering precise and flexible fuel injection for each operating condition. Injection pressures commonly exceed 1600–2000 bar (23,200–29,000 psi) depending on emissions tier. The low-pressure lift pump supplies fuel to a high-pressure pump, which maintains rail pressure under ECM command. Electronically actuated injectors perform multiple injection events–including pilot, main, and post-injection–to optimize combustion, reduce noise, minimize emissions, and improve throttle response.
The electronic control module (ECM) continuously monitors sensors including crankshaft position, camshaft position, rail pressure, boost pressure, coolant temperature, intake temperature, exhaust temperature, and NOx sensors in emissions-equipped variants. These inputs control injection timing, quantity, pressure, turbocharger performance, and regeneration cycles for aftertreatment systems. Fuel filtration includes primary and secondary filters with water separation capability.
| Lubrication System |
The lubrication system is a full-pressure wet-sump configuration powered by a gear-driven oil pump. Oil is drawn through a mesh strainer, filtered by a full-flow filter, and distributed throughout the engine via the main oil gallery. Lubrication targets include crankshaft bearings, rod journals, camshaft bearings, rocker arms, turbocharger bearings, and accessory drives. Piston cooling jets regulate crown temperature during high-load cycles.
Normal operating oil pressure typically ranges from 300 to 500 kPa (44–72 psi), while idle pressure usually falls between 100 and 150 kPa (15–22 psi). Oil capacity ranges from 11 to 18 liters (11.6–19 US quarts) depending on sump configuration. Engines equipped with DPF require low-ash lubrication oil to protect the aftertreatment.
| Cooling System |
The QSB6.7 uses a liquid-cooling system comprising a belt-driven centrifugal water pump, cast-in coolant passages, thermostat, radiator, and pressurized expansion tank. The thermostat begins opening near 82°C (180°F) and is fully open around 95°C (203°F). Cooling system pressure is typically between 90 and 110 kPa (13–16 psi). Coolant capacity generally ranges between 15 and 25 liters (15.8–26.4 US quarts), depending on installation.
Air-to-air or air-to-water charge-air cooling is used to reduce intake air temperature, enhancing combustion stability and power output. The ECM monitors coolant temperature and controls derating or shutdown procedures to prevent overheating. Proper coolant chemistry is essential to prevent corrosion, cavitation, scaling, and liner pitting.
| Other Systems |
The turbocharging system may employ a wastegate or variable-geometry turbocharger (VGT) depending on emissions tier. VGT systems provide precise control of boost pressure, improved transient performance, and efficient exhaust backpressure management for aftertreatment support. Charge-air cooling improves density and reduces thermal stress.
Heavy-duty intake filtration, including dual-stage filters for severe-duty applications, protects the engine from particulate ingress. Exhaust aftertreatment systems may include DOC (Diesel Oxidation Catalyst), DPF (Diesel Particulate Filter), SCR (Selective Catalytic Reduction), ammonia slip catalyst, and EGR (Exhaust Gas Recirculation). Electrical systems may use 12- or 24-volts with alternators rated between 60 and 150 amperes. The ECM provides continuous diagnostics, fault-code monitoring, and service alerts, aiding maintenance and operational uptime.
| Dimensions and Weight |
Physical dimensions include:
Length 1050–1250 mm (41.3–49.2 inches)
Width 700–900 mm (27.6–35.4 inches)
Height 1000–1250 mm (39.4–49.2 inches)
Dry weight generally ranges from 480 to 590 kg (1058–1301 lbs),
depending on emissions equipment, turbocharger type, and
application-specific accessories. Despite its displacement, the engine
offers a relatively compact packaging suitable for modern equipment
bays.
| Maintenance Data |
Oil and filter replacement intervals for the QSB6.7 typically occur every 500 hours under normal duty cycles, with more frequent changes recommended for severe service. Fuel filters should be replaced every 500 hours, with water separators drained routinely. Air filters require maintenance every 250–500 hours depending on dust exposure. Coolant replacement intervals depend on coolant chemistry but generally occur every two years or during major service.
Valve lash inspection may be required on non-hydraulic-lash variants. Aftertreatment-equipped engines require regular DPF regeneration cycles and periodic cleaning depending on duty cycle. The ECM stores detailed operational data useful for predictive maintenance, troubleshooting, and performance optimization.
| Tightening Torques |
Cylinder head bolts: 180–210 Nm (133–155 lb-ft)
Main bearing cap bolts: 150–180 Nm (111–133 lb-ft)
Connecting rod bolts: 70–90 Nm (52–66 lb-ft)
Flywheel bolts: 220–260 Nm (162–192 lb-ft)
Crankshaft pulley bolt: 240–280 Nm (177–207 lb-ft)
Injector hold-down: 20–25 Nm (15–18 lb-ft)
Glow plugs or intake heaters: 10–15 Nm (7–11 lb-ft)
Oil drain plug: 30–40 Nm (22–30 lb-ft).
| Vehicle Applications |
The Cummins QSB6.7 powers a wide variety of heavy-duty and mid-size equipment including agricultural tractors, excavators, wheel loaders, forestry processors, compactors, mining support trucks, telehandlers, cranes, generator sets, industrial pumps, drilling rigs, specialized marine support machinery, and other off-highway platforms. Its balance of strong torque, compact dimensions, modern emissions capability, electronic control, and long-term durability makes it suitable for demanding industrial environments worldwide.
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