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Detroit Diesel 12V71T Specifications
| Engine Model: Detroit Diesel 12V71T |
| Engine Type: 2-stroke 12-cylinder turbocharged liquid-cooled uniflow-scavenged diesel |
| Total Displacement: 852 cu.in (13.9 L) |
| Rated Engine Power: 850-1100 Hp (630-815 kW) at 2300 rpm |
| Fuel System Type: Mechanical unit injector |
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| General Technical Data |
The Detroit Diesel 12V71T is a two-stroke,
turbocharged, V12 diesel engine with unit injectors. This engine
represents a large-displacement, high-power variant within Detroit
Diesel's iconic "71 Series" of two-stroke engines. Production spanned
from the 1960s through the 1990s. The 12V71T is a true two-stroke
design, relying on a Roots-type positive displacement blower for
scavenging air, supplemented by exhaust-driven turbochargers to increase
charge density.
It is constructed with a cast-iron cylinder block with wet cylinder
liners and individual cast-iron cylinder heads. The engine operates on
the uniflow scavenging principle, where air enters through ports in the
cylinder liner and exhaust exits through poppet valves in the cylinder
head.
The 12V71T is characterized by its immense power output, high fuel
consumption, and unmistakable turbo-and-blower sound. It is a
non-interference engine design. This engine was employed in heavy-duty
applications such as marine propulsion, large generator sets, and heavy
hauling trucks where maximum power density and torque were required.
General Engine Data
Engine Type: Two-stroke, 45-degree V12, liquid-cooled, turbocharged and
blower-scavenged diesel engine. Bore: 108.0 mm (4.25 in). Stroke: 127.0
mm (5.00 in).
Displacement: 13965 cc (852 cu.in).
Compression Ratio: 18.7:1.
Firing Order: 1L-6R-5L-2R-3L-4R-6L-1R-2L-5R-4L-3R (where L is left bank,
R is right bank).
Cylinder Numbering: Left bank cylinders are 1L-2L-3L-4L-5L-6L (front to
rear). Right bank cylinders are 1R-2R-3R-4R-5R-6R (front to rear).
Engine Rotation (viewed from the flywheel end): Clockwise.
Aspiration: Gear-driven Roots-type positive displacement blower plus one
or two exhaust-driven turbochargers. Fuel Requirement: Diesel fuel,
Number 2-D.
Power Output: Ranges from 850 Hp at 2100 RPM to 1100 Hp at 2300 RPM
(630-815 kW), depending on turbocharger configuration, injector size,
and application.
Torque Output: Ranges from 2250 lb-ft at 1600 RPM to 2750 lb-ft at 1600
RPM.
Governed Speed: 2100-2300 RPM.
Scavenging Air Pressure: 6-10 psi (0.41-0.69 bar) above atmospheric.
Oil Pressure (at operating temperature): 40-60 psi (2.8-4.1 bar) at 2000
RPM.
| Cylinder Block |
The cylinder block is a complex cast-iron structure forming a 45-degree
V configuration. It consists of a massive lower crankcase and an upper
structure supporting the cylinder liners. The block uses removable wet
cylinder liners made of cast iron. Each liner is sealed at the top by a
copper gasket and at the bottom by synthetic rubber O-rings. The liners
feature a series of precision intake ports around their circumference.
The crankshaft is a forged steel unit with seven main bearings.
Connecting rods are forged steel, with the big end using shell-type
bearing inserts. Pistons are aluminum alloy with a Ni-Resist iron insert
in the top ring groove to withstand the extreme heat of two-stroke
combustion. Each piston uses four rings. The piston pin is
full-floating, retained by circlips.
| Cylinder Head and Valves |
Each cylinder has a separate cast-iron cylinder head. The cylinder head
contains two exhaust valves, a unit injector, and a glow plug or air
starting valve assembly. The head does not contain intake valves. The
exhaust valves are actuated by pushrods and rocker arms from a camshaft
located in the V of each cylinder bank. The valve train is adjustable.
Valve seats and guides are replaceable. The cylinder head seals against
the wet liner with a composite steel-asbestos or modern equivalent head
gasket.
Valve Train Data
Valve Arrangement: Two exhaust valves per cylinder (24 total). No intake
valves.
Exhaust Valve Head Diameter: 44.5 mm (1.75 in).
Exhaust Valve Stem Diameter: 11.1 mm (0.437 in).
Valve Lift: 12.7 mm (0.50 in).
Valve Lash (Clearance): 0.38 mm (0.015 in) cold, adjusted at the rocker
arm.
Camshaft Drive: Gear-driven from the crankshaft via an intermediate
idler gear train.
| Fuel System |
The fuel system is a mechanical, camshaft-actuated unit injector system. Each cylinder has a self-contained unit injector. The injector is actuated by a dedicated lobe on the camshaft via a pushrod and rocker arm. Fuel is supplied to the injectors by a gear-type transfer pump at low pressure (30-50 psi / 2-3.5 bar).
Injection timing is fixed, set by the camshaft and injector pushrod
adjustment. Fuel rate (engine power) is controlled by a mechanical
governor connected to a control rack that rotates all injector plungers
simultaneously to change effective stroke. A hand primer pump is used
for system bleeding.
Fuel System Data
Fuel Injection Type: Mechanical unit injector.
Injection Pressure: Generated internally by the unit injector, up to
20,000 psi (1379 bar).
Injector Actuation: Mechanical, via camshaft, pushrod, and rocker arm.
Governor: Mechanical centrifugal governor, mounted on the blower drive
housing.
Fuel Transfer Pump: Gear-type, engine-driven.
| Lubrication System |
The lubrication system is a pressure-fed, wet-sump design. A gear-type oil pump, driven from the camshaft gear train, draws oil from the sump. Oil is routed through a full-flow oil filter and an oil cooler. Pressure is regulated by a spring-loaded relief valve.
Lubrication is provided to the crankshaft main and rod bearings,
camshaft bearings, blower drive gears, the blower itself, and the
turbocharger(s) center section. The unit injector rocker arms and
exhaust valve rocker arms are lubricated via oil galleries. The system
includes a water-cooled oil cooler.
Lubrication System Data
Oil Pump Type: Gear-type, camshaft gear-driven.
Oil Capacity (wet sump): 55 US quarts (52 liters).
Oil Filter Type: Replaceable spin-on canister or cartridge type.
Oil Type (recommended): High-quality diesel engine oil, SAE 40 or 15W-40
for multi-grade, meeting API Service Classification CD or later.
Oil Change Interval: 100-250 hours of operation, depending on service
severity.
| Cooling System |
The cooling system is a pressurized, pump-driven system. A centrifugal water pump, gear-driven from the front of the engine, circulates coolant. Coolant flows through the cylinder block water jackets, the cylinder heads, the oil cooler, and the turbocharger(s) cooling jacket.
Thermostats regulate coolant temperature, opening at 160-180°F
(71-82°C). The system is designed for use with a heat exchanger in
marine applications or a radiator in vehicular applications. A coolant
conditioner (Supplemental Coolant Additive - SCA) is required to
maintain proper chemistry and prevent liner cavitation erosion.
Cooling System Data
Cooling System Type: Pressurized, gear-driven pump, with thermostatic
control.
Coolant Capacity (engine only): 25 US quarts (23.7 liters) - system
capacity is significantly larger with external components.
Thermostat Opening Temperature: 180°F (82°C).
Water Pump Drive: Gear-driven from the front gear train.
| Other Systems |
Air System (Scavenging and
Turbocharging)
A Roots-type positive displacement blower is gear-driven from the front
of the engine, providing the baseline scavenging air. One or two
exhaust-driven turbochargers are installed in series with the blower.
The turbocharger(s) compress intake air, which is then fed into the
blower inlet, increasing the density of air delivered to the cylinders.
This "Turbocharged-Aftercooled" or "Twin-Turbo" configuration
significantly increases power output over a naturally aspirated or
blower-only 12V71.
Starting System
The engine uses a 24-volt or 32-volt DC electric starting system with
multiple starters. Cold weather starting is assisted by ether injection
systems (cylinder primers) or by intake air heaters. Many marine and
stationary versions use direct air starting, where compressed air is
admitted directly into the cylinders via starting valves in the heads.
| Dimensions and Weight |
Overall Length: 2050 mm (80.7 in).
Overall Width: 1350 mm (53.1 in).
Overall Height: 1650 mm (65.0 in).
Approximate Dry Weight: 2850 kg (6280 lbs).
| Maintenance Data |
Engine Oil and Filter Change: Every 100 hours for severe service; up to
250 hours for steady-state marine or generator operation.
Oil Analysis: Mandatory for establishing optimal change intervals and
monitoring wear.
Air Filter Service: Clean/replace as indicated by restriction gauge;
critical in all environments.
Valve Lash Adjustment: Check and adjust every 500 hours of operation.
Injector Timing/Rack Setting: Check and adjust every 1000 hours or if
performance issues arise.
Blower Drive Gear Lash: Check every 1000 hours.
Turbocharger Inspection: Check for axial and radial play every 1000
hours.
Coolant SCA Level: Test every 250 hours; replenish as needed.
Wet Liner O-Rings: Inspect/replace during major overhauls; coolant in
oil indicates failure.
| Tightening Torques |
Cylinder Head Bolts: 140-160 lb-ft (190-217 Nm). Tighten in a specific
sequence to specification.
Main Bearing Cap Bolts: 275-300 lb-ft (373-407 Nm).
Connecting Rod Nut: 65-70 lb-ft (88-95 Nm).
Unit Injector Hold-Down Clamp Bolt: 35-40 lb-ft (47-54 Nm).
Rocker Arm Shaft Bracket Bolts: 35-40 lb-ft (47-54 Nm).
Oil Pan Bolts: 25-30 lb-ft (34-41 Nm).
Blower Drive Gear Nut: 350-400 lb-ft (475-542 Nm).
Water Pump Housing Bolts: 35-40 lb-ft (47-54 Nm).
| Machinery Applications |
The Detroit Diesel 12V71T engine was installed in the most demanding heavy-duty equipment: Marine Propulsion: High-speed ferries, tugboats, fishing vessels, and medium-sized commercial ships as primary propulsion. Generator Sets: Prime power and standby generators in the 800-1000 kW range.
Heavy Haul Trucks: Off-highway haul trucks in mining and heavy construction (e.g., Euclid, Dart, and custom chassis). Locomotives: In some diesel-electric locomotive applications, often as a prime mover for smaller switchers or industrial units. Military Applications: In large landing craft and other naval auxiliaries.
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