Mitsubishi 6DB1 Specifications
| Engine Model: Mitsubishi 6DB1 |
| Engine Type: 4-cycle inline 6-cylinder liquid-cooled diesel |
| Total Displacement: 522 cu.in (8.55 L) |
| Rated Engine Power: 163-217 Hp (121-162 kW) at 2300 rpm |
| Fuel System Type: Direct injection |
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The Mitsubishi 6DB1 is an 8.5-liter, inline
6-cylinder diesel engine belonging to the Mitsubishi DB series.
Introduced in the 1960s and produced through the 1980s, this engine
became a cornerstone for Mitsubishi Fuso's heavy-duty truck and bus
lines. The 6DB1 engine family includes the naturally aspirated 6DB1 and
the turbocharged 6DB1AT variant. Known for robust cast-iron construction
and a gear-driven timing system, this powerplant was engineered for
extreme durability in industrial and commercial environments.
The engine's architecture prioritizes serviceability and sustained
high-load operation, making it suitable for applications ranging from
heavy-duty trucks to construction machinery and stationary generator
sets. The 6DB1's long-stroke design (150 mm stroke) contributes to
favorable torque characteristics at lower engine speeds, a valued
attribute for off-highway and commercial vehicle operation.
The Mitsubishi 6DB1 engine is recognized for its industrial-grade
durability, straightforward mechanical design, and high torque output at
low engine speeds. The cast-iron cylinder block with wet replaceable
liners permits in-frame overhauls, a significant advantage for fleet
operators seeking extended service life. The gear-driven camshaft
eliminates belt or chain failures, while the mechanical in-line
injection pump delivers reliable fuel metering without electronic
complexity.
The OHV valvetrain with two valves per cylinder offers a balance between
power output and maintenance simplicity. The turbocharged 6DB1AT variant
provides a substantial torque increase over the naturally aspirated
version, improving gradeability and acceleration in heavy truck
applications. The engine's dry weight of approximately 386 kg (851 lb)
reflects its heavy-duty construction. Service considerations include
regular valve clearance adjustment and adherence to injection pump
timing specifications.
Engine Type: Inline 6-cylinder, 4-cycle, water-cooled diesel engine.
Displacement: 8.55 liters (8,550 cc, 522 cu.in).
Bore: 110.0 mm (4.33 in).
Stroke: 150.0 mm (5.91 in). Some early variants utilize a 115.0 mm (4.53
in) stroke.
Compression Ratio: 17.5:1 to 18.5:1, varying with piston design and
application.
Combustion System: Direct injection.
Valvetrain: OHV (Overhead Valve), 2 valves per cylinder (12 total).
Camshaft Drive: Gear train from crankshaft.
Firing Order: 1-5-3-6-2-4.
Rotation (from flywheel end): Counter-clockwise.
Naturally Aspirated (6DB1)
Maximum Power: 121 kW (165 PS, 163 hp) @ 2,300 rpm.
Maximum Torque: 447 Nm (330 lb-ft) @ 1,600 rpm.
Governed Speed Range: 1,000-2,500 rpm.
Turbocharged (6DB1AT)
Maximum Power: 162 kW (220 PS, 217 hp) @ 2,200-2,300 rpm.
Maximum Torque: Up to 686 Nm (506 lb-ft) @ 1,200-1,600 rpm.
Governed Speed Range: 1,000-2,500 rpm.
Generator Set Ratings (60 Hz)
6DB1 (Naturally Aspirated): 70-80 kW (88-100 kVA) continuous @ 1,800
rpm.
6DB1AT (Turbocharged): 100-125 kW (125-156 kVA) continuous @ 1,800 rpm.
The cylinder block is constructed from cast iron with an open-deck
design to accommodate replaceable wet cylinder liners. Each liner is
precision-machined from centrifugally cast iron, surface-hardened, and
replaceable without machining the block. The wet liner design allows
coolant to circulate directly around each cylinder bore, providing
superior heat transfer from the combustion chamber to the cooling
system. Liners are sealed at the bottom with rubber O-rings and at the
top with a compressed copper or steel gasket.
The block features seven main bearing webs supporting a forged steel
crankshaft with seven main bearings. The crankshaft is
induction-hardened at the journal surfaces and features eight
counterweights for vibration control. The block incorporates integrated
oil galleries supplying the main bearings, connecting rod bearings,
camshaft bearings, and piston cooling jets. The timing gear housing is
integrated into the front of the block.
The cylinder head is manufactured from cast iron and houses the overhead
valve (OHV) arrangement with two valves per cylinder. The cross-flow
design positions intake ports on one side and exhaust ports on the
opposite side, improving volumetric efficiency and cooling of the
exhaust valve area. Intake valves measure 45.0 mm (1.77 in) in diameter,
while exhaust valves measure 40.0 mm (1.57 in). The valvetrain consists
of a single camshaft located in the cylinder block, operating the valves
through hardened pushrods and forged steel rocker arms.
Valve seat inserts are replaceable and manufactured from sintered alloy
material for wear resistance. Valve clearance is adjusted by a screw and
locknut on each rocker arm. The cylinder head is secured by four head
bolts per cylinder (24 total), requiring a multi-step torque sequence.
The cylinder head incorporates the direct injection combustion chambers
with recessed bowls in the piston crowns.
The fuel system employs a mechanical direct injection architecture using
an in-line injection pump (Bosch A-type or P-type, or Mitsubishi-built
equivalent). The injection pump is flange-mounted to the timing gear
housing and driven by the engine's gear train. The in-line pump design
provides individual plungers and barrels for each cylinder, delivering
precise fuel metering across the engine speed range. A mechanical
governor, integrated into the injection pump, maintains engine speed
under varying loads through a centrifugal weight mechanism.
A vacuum-operated or mechanical boost compensator is fitted on
turbocharged 6DB1AT variants to adjust fuel delivery under boost
conditions. High-pressure injection lines deliver fuel to multi-hole
injectors mounted in each cylinder head. Injector opening pressure is
factory set between 150 and 180 bar (2,175-2,610 psi). A mechanical fuel
feed pump, mounted on the injection pump or cylinder block, draws fuel
from the tank and supplies it through primary and secondary fuel
filters.
The lubrication system is a forced-feed, wet-sump type utilizing a
gear-type oil pump mounted to the front timing gear housing. The pump is
driven by the crankshaft gear, ensuring immediate oil pressure upon
startup. Oil is drawn from a cast aluminum or stamped steel oil pan
through a strainer before pressurization. A full-flow spin-on oil filter
is mounted externally on the cylinder block.
The system supplies lubricant to the crankshaft main bearings,
connecting rod bearings, camshaft bearings, timing gears, pushrods,
rocker shaft, valve tips, and in turbocharged variants, the turbocharger
center bearing. The oil pump incorporates a pressure relief valve set
between 3.5 and 4.5 bar (50-65 psi) at rated speed. The oil pan capacity
supports extended operation with a dipstick on the side of the block
indicating oil level. A full-flow oil cooler is fitted on heavy-duty
truck and industrial applications.
The cooling system is a pressurized, water-cooled setup utilizing a
centrifugal water pump driven by the engine's accessory belt. A wax-type
thermostat with a rated opening temperature of 76°C (169°F) or 82°C
(180°F) regulates the engine operating temperature. Coolant circulates
through the cast-iron cylinder block, around the wet cylinder liners,
through the cast-iron cylinder head, and in turbocharged variants,
through the turbocharger bearing housing before passing through a
radiator.
A belt-driven cooling fan, mounted to the water pump pulley, provides
airflow across the radiator. The system incorporates a pressurized
expansion tank or radiator cap rated for 0.7-1.0 bar (10-15 psi). The
coolant capacity varies by application, with truck installations
typically holding 15-20 liters (16-21 qt).
| Intake and Exhaust Systems |
Intake System: Air is drawn through a dry-type paper element air filter
(often a two-stage cyclone pre-cleaner in dusty applications) before
entering the intake manifold. The intake manifold is cast separately and
mounts to the side of the cylinder head. Turbocharged 6DB1AT variants
include an air-to-air intercooler mounted at the front of the vehicle.
Exhaust System: A cast-iron exhaust manifold collects gases and directs
them to a single outlet. In turbocharged variants, the turbocharger is
flange-mounted between the exhaust manifold and the exhaust pipe. A
flexible bellows section may be present to accommodate thermal
expansion.
Timing System: The camshaft is driven by a gear train from the
crankshaft. Hardened steel timing gears at the front of the engine
provide fixed timing without belts or chains requiring replacement. The
gear train sequentially drives the crankshaft gear, idler gear, camshaft
gear, and injection pump gear. Timing marks on each gear must align
during assembly. No timing tensioner is present due to the fixed gear
arrangement.
Starting System: A 24-volt electric starter motor is mounted to the
flywheel housing, engaging a ring gear on the flywheel. The 24V system
provides higher cranking power for diesel engines in cold conditions and
heavy inertia loads. A 24V alternator with output of 25-35 amperes
(heavy-duty variants up to 50 amperes) maintains battery charge.
Turbocharging System (6DB1AT): A fixed-geometry turbocharger (Mitsubishi
TD series or equivalent) is flange-mounted to the exhaust manifold. The
turbocharger utilizes exhaust gas energy to compress intake air,
increasing volumetric efficiency and power output. The turbocharger
bearing housing is supplied with engine oil through a dedicated feed
line.
Glow Plug / Intake Heater: An intake manifold grid heater or individual
cylinder glow plugs provide cold starting assistance. The 24V electrical
system supports rapid heating of the intake air in cold climates.
Overall Engine Length: 1,200 mm (47.2 in) from front timing cover to
flywheel housing.
Overall Engine Width: 680 mm (26.8 in).
Overall Engine Height: 950 mm (37.4 in) from oil pan bottom to rocker
cover top.
Dry Weight: 386 kg (851 lb), inclusive of the flywheel, intake manifold,
exhaust manifold, starter motor, and alternator. Turbocharged 6DB1AT
adds approximately 30 kg (66 lb).
Engine Oil Capacity (with Filter): 15-18 liters (16-19 U.S. qt, 13-16
imperial qt), varying with oil pan configuration and oil cooler
presence. Engine Oil Specification: API CD, CE, CF-4, or CG-4 grade; SAE
15W-40 or SAE 10W-30 viscosity recommended. SAE 30 or SAE 40
single-grade oils may be used in warm climates. Oil Change Interval
(Truck Application): 5,000-10,000 km (3,100-6,200 mi) or 200-250
operating hours. Oil Change Interval (Industrial Stationary): 250-500
operating hours, depending on duty cycle. Fuel Filter Replacement
Interval: 10,000 km (6,200 mi) or 250 operating hours.
Coolant Capacity: 15-20 liters (16-21 qt) inclusive of the radiator and
engine block, varying by application. Coolant Specification: Ethylene
glycol-based antifreeze with supplemental coolant additive (SCA) for wet
sleeve cylinder liner protection. Nitrite-containing coolant is required
for cavitation prevention. Thermostat Opening Temperature: 76°C (169°F)
or 82°C (180°F) depending on application. Air Filter Service: Dry
element replacement when restriction indicator shows vacuum exceeding
635 mm water gauge (25 in H2O) or at 500 hours.
Valve Clearance (Cold): Intake: 0.25 mm (0.010 in); Exhaust: 0.35 mm
(0.014 in) for naturally aspirated variants. Turbocharged variants may
specify intake: 0.30 mm (0.012 in); exhaust: 0.40 mm (0.016 in).
Adjustment is performed by loosening the rocker arm locknut and turning
the adjusting screw while holding the appropriate feeler gauge. Valve
Clearance Inspection Interval: 10,000 km (6,200 mi) or 250 operating
hours.
Injector Inspection Interval: 1,000 operating hours for opening pressure
testing, spray pattern inspection, and flow testing. Injection Pump
Timing: Static timing set at 18-20 degrees before top dead center for
naturally aspirated variants; 16-18 degrees before top dead center for
turbocharged variants. Timing is verified by aligning marks on the pump
flange and timing gear housing or by using a dial indicator on the pump
plunger. Wet Cylinder Liner Protrusion: 0.05-0.15 mm (0.002-0.006 in)
above the block deck, measured with a dial indicator and straight edge.
Cylinder Head Bolts, Step 1: 50 Nm (5.1 kgf-m, 37 lb-ft).
Cylinder Head Bolts, Step 2: 100 Nm (10.2 kgf-m, 74 lb-ft).
Cylinder Head Bolts, Step 3: 160 Nm (16.3 kgf-m, 118 lb-ft).
Main Bearing Cap Bolts: 180 Nm (18.4 kgf-m, 133 lb-ft).
Connecting Rod Cap Bolts: 100 Nm (10.2 kgf-m, 74 lb-ft).
Flywheel Bolts: 120 Nm (12.2 kgf-m, 89 lb-ft).
Crankshaft Pulley Bolt: 300 Nm (30.6 kgf-m, 221 lb-ft).
Camshaft Bearing Cap Bolts: 20 Nm (2.0 kgf-m, 15 lb-ft).
Rocker Arm Shaft Bolts: 35 Nm (3.6 kgf-m, 26 lb-ft).
Intake Manifold Bolts: 25 Nm (2.5 kgf-m, 18 lb-ft).
Exhaust Manifold Nuts: 30 Nm (3.1 kgf-m, 22 lb-ft).
Injection Pump Mounting Nuts: 25 Nm (2.5 kgf-m, 18 lb-ft).
Injector Hold-Down Clamp Bolts: 30 Nm (3.1 kgf-m, 22 lb-ft).
Turbocharger Mounting Nuts (6DB1AT): 45 Nm (4.6 kgf-m, 33 lb-ft).
Oil Filter (Spin-on Type): 18 Nm (1.8 kgf-m, 13 lb-ft).
Oil Pan Bolts: 20 Nm (2.0 kgf-m, 15 lb-ft).
Timing Gear Cover Bolts: 15 Nm (1.5 kgf-m, 11 lb-ft).
Starter Motor Mounting Bolts: 45 Nm (4.6 kgf-m, 33 lb-ft).
The Mitsubishi 6DB1 and 6DB1AT engines were utilized across Mitsubishi
Fuso truck and bus lineups, as well as in construction machinery and
industrial stationary power applications from the 1960s through the
1980s.
Mitsubishi Fuso Trucks (Medium and Heavy
Duty)
Fuso T-series (T33, T37, T38): Medium-duty cab-over trucks for general
freight and construction.
Fuso FK series: Medium-duty trucks in the Mitsubishi Fuso lineup.
Fuso FM series: Heavy-duty trucks for long-haul and regional
distribution.
Fuso FV series: Large-capacity trucks for heavy haulage.
Mitsubishi Canter (early models): Some heavy-duty Canter variants
utilized the 6DB1 engine.
Buses
Fuso B820J: Heavy-duty bus chassis for intercity and tourist
applications.
Fuso MR520: Rear-engine bus configuration for urban transit.
Fuso MP series: Coach and bus chassis in Asian and export markets.
Construction and Earthmoving Equipment
Mitsubishi MG3 and MG300 Motor Graders: Road construction and
maintenance equipment.
Mitsubishi MS230 Excavator: Large hydraulic excavator for civil works.
Mitsubishi BS series wheel loaders: Heavy-duty loading equipment.
PandH Kobelco 435 TC Crane: Truck-mounted crane with the 6DB1 engine.
Kobelco excavators: Various models utilizing the 6DB1 as a power unit.
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