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Cummins N14 Specifications
| Engine Model: Cummins N14 |
| Engine Type: 4-cycle inline 6-cylinder direct injection liquid-cooled diesel |
| Total Displacement: 855 cu.in (14 L) |
| Rated Engine Power: 205-525 Hp (153-391 kW) at 2000 rpm |
| Aspiration Type: Turbocharged |
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| General Technical Data |
0The Cummins N14 is one of the most iconic heavy-duty diesel engines ever produced, widely used in on-highway trucks, construction equipment, industrial machinery, and generator-set applications. Its reputation for exceptional durability, long overhaul life, simple mechanical and electronic variants, and broad parts availability has made it a workhorse across multiple industries for decades.
Based on the earlier Cummins 855 platform, the
N14 integrates improved cooling, refined combustion geometry, enhanced
fuel systems, and stronger structural components. The engine’s modular
design, mechanical and electronic fuel system options, and reliable
performance under severe-duty conditions contribute to its legendary
status among fleet owners, operators, and service technicians.
The Cummins N14 is a four-stroke, inline six-cylinder diesel engine with
a displacement of approximately 14.0 liters (855 cubic inches). Bore
generally measures 140 mm (5.51 inches), while stroke is approximately
152 mm (5.98 inches), forming a long-stroke design optimized for
extremely high torque output and fuel efficiency. Horsepower ratings
vary widely depending on calibration, ranging from roughly 205 to 525
horsepower (153–391 kW) at around 1700–2100 rpm.
Peak torque ratings typically fall between 1350
and 1850 Nm (996–1365 lb-ft), often achieved at 1200–1400 rpm.
Compression ratio commonly ranges around 17:1 depending on model
version. Earlier N14 engines used mechanical PT (Pressure-Time) fuel
systems, while later models adopted electronic control units (N14 Celect
and Celect Plus). The firing order is 1–5–3–6–2–4, and idle speed
typically ranges between 600 and 650 rpm.
The N14 features a high-strength cast-iron cylinder block built to
support the massive internal pressures associated with heavy-duty
operation. Reinforcement ribs improve rigidity and reduce torsional
stresses during extended full-load cycles. The block accommodates wet
cylinder liners that improve cooling efficiency and support easy
overhaul without machining the block. The forged-steel crankshaft is
supported by seven large main bearings engineered for long-term
durability.
Precision-machined oil galleries distribute
lubrication to critical rotating components, and coolant jackets cast
around each cylinder ensure consistent thermal management under varying
load conditions. Threaded mounting points allow integration with truck
frames, generator housings, and industrial equipment.
The cast-iron cylinder head contains direct-injection combustion
chambers optimized for both mechanical and electronic fuel-injection
systems. Each cylinder includes two intake and two exhaust valves
actuated by pushrods and rocker arms driven by a block-mounted camshaft.
Valve lash is adjustable and must be checked at regular intervals.
Hardened valve seats and wear-resistant valve guides withstand the extreme thermal cycling common in heavy-duty diesel operation. The combustion chamber geometry promotes strong swirl and efficient fuel-air mixing, improving combustion quality and reducing soot. Integrated coolant passages help maintain stable head temperature, reducing the likelihood of cracks and extending long-term service life.
| Fuel System |
Earlier N14 engines use a mechanical PT (Pressure-Time) fuel system.
This system employs a gear-driven PT pump that meters fuel flow based on
pressure and injector orifice timing. Fuel flows through a transfer
pump, filters, and then to injectors that meter injection timing
mechanically. PT systems are known for durability, simple servicing, and
reliable operation.
Later N14 Celect and Celect Plus versions incorporate electronic control
modules (ECMs), electronically actuated injectors, and advanced timing
control. Electronic injection provides better throttle response,
improved fuel economy, lower emissions, and enhanced diagnostic
capability. Injectors use electronically controlled solenoids to meter
fuel precisely.
ECMs monitor engine speed, load, coolant temperature, boost pressure, fuel temperature, intake temperature, and other sensor feedback to optimize injection timing and delivery. Filtration includes primary and secondary fuel filters to protect injectors and pumps from contamination. Fuel pressures vary significantly depending on PT or electronic systems, but all configurations ensure accurate combustion under heavy load.
| Lubrication System |
The lubrication system is a full-pressure wet-sump design powered by a gear-driven oil pump. Oil is drawn through a mesh strainer and forced through full-flow and bypass filters before reaching critical engine components. Lubrication is supplied to crankshaft bearings, connecting rod journals, camshaft bearings, rocker arms, turbocharger bearings, and accessory drives.
Many N14 engines feature piston cooling jets to regulate temperatures during prolonged heavy-duty cycles. Typical oil pressure ranges from 275 to 450 kPa (40–65 psi) at rated speed and around 100–150 kPa (15–22 psi) at idle. Oil capacity is commonly between 38 and 45 liters (40–47.5 US quarts). High-quality heavy-duty diesel oil meeting API CF or higher classifications are required.
| Cooling System |
The cooling system is a liquid-based design using a belt-driven centrifugal water pump. Coolant flows through block and head passages, absorbing combustion heat and stabilizing engine temperature. The thermostat typically begins opening around 82°C (180°F) and is fully open near 95°C (203°F). Cooling system pressure usually ranges from 90 to 110 kPa (13–16 psi).
Coolant capacity varies depending on equipment configuration but commonly ranges between 45 and 60 liters (47.5–63.4 US quarts). Many N14 engines use air-to-air charge-air coolers (intercoolers) to reduce intake temperatures, enhancing torque and minimizing combustion stress. Proper coolant chemistry prevents corrosion, scale, and cavitation around wet liners.
| Other Systems |
Turbocharging increases air density and supports high torque output. Wastegated turbochargers or fixed-geometry units may be used depending on model. Charge-air cooling improves performance and emissions. The intake system incorporates heavy-duty dry-element air filters with optional dual-stage filtration for dusty conditions. The exhaust manifold is cast iron designed for high-temperature stability.
Electrical systems are generally 12-volt or 24-volt, with alternators ranging between 60 and 120 amperes. Electronic versions include ECM-controlled sensors that support diagnostics, fault detection, and improved engine protection features. PTO drives, hydraulic pump mounts, and front-end accessory drives offer broad application flexibility.
| Dimensions and Weight |
Engine dimensions include:
Length: 1400–1600 mm (55.1–63.0 inches)
Width: 900–1100 mm (35.4–43.3 inches)
Height: 1150–1400 mm (45.3–55.1 inches)
Dry weight commonly ranges between 1,200 and 1,450 kg (2,645–3,197 lbs),
depending on emissions equipment, turbocharger type, aftercooler
configuration, and accessory package. Despite its size, the N14
maintains a serviceable layout for technicians.
| Maintenance Data |
Oil and filter replacement intervals typically occur every 250–400 hours for industrial or generator applications, or every 15,000–30,000 km (9,300–18,600 miles) in on-highway service depending on duty cycle. Fuel filters must be replaced every 250–400 hours. Air filter service depends on environmental dust levels but commonly occurs every 100–300 hours. Valve lash inspection is recommended every 500–600 hours.
Cooling system flushing is required every two years or 2,000 hours. PT and electronic injector servicing typically occurs every 1,500–2,000 hours. Pump calibration, electronic diagnostics, and timing verifications are recommended at major service intervals. Compression testing is often performed at around 4,000–5,000 hours to evaluate internal wear.
| Tightening Torques |
Cylinder head bolts: 270–310 Nm (199–229 lb-ft)
Main bearing cap bolts: 260–300 Nm (192–221 lb-ft)
Connecting rod bolts: 120–150 Nm (89–111 lb-ft)
Flywheel bolts: 400–450 Nm (295–332 lb-ft)
Crankshaft pulley bolt: 300–350 Nm (221–258 lb-ft)
Injector hold-down bolts: 25–30 Nm (18–22 lb-ft)
Intake heater or glow plug (if equipped): 10–15 Nm (7–11 lb-ft)
Oil drain plug: 50–60 Nm (37–44 lb-ft).
| Vehicle Applications |
The Cummins N14 powers long-haul trucks, vocational trucks, mining haulers, construction machinery, agricultural equipment, large generator sets, industrial pumps, and marine auxiliary systems. Its combination of extreme durability, high torque output, broad parts support, and mechanical simplicity in early variants has made it a legendary platform for heavy-duty applications worldwide.
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