Mitsubishi K3H Specifications
| Engine Model: Mitsubishi K3H |
| Engine Type: 4-cycle inline 3-cylinder naturally aspirated liquid-cooled diesel |
| Total Displacement: 78.7 cu.in (1.29 L) |
| Rated Engine Power: 28 Hp (21 kW) at 2700 rpm |
| Fuel System Type: Direct injection |
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The Mitsubishi K3H is a compact, 3-cylinder,
vertical, water-cooled diesel engine from Mitsubishi’s K-series engine
family. Produced from the early 1980s through the 1990s, this engine was
engineered for agricultural and construction applications where
durability, fuel economy, and ease of maintenance are prioritized over
maximum power output. The naturally aspirated diesel displaces 1.290
liters (1,290 cc) from a bore and stroke of 78 mm x 90 mm - an
undersquare configuration favoring torque production at lower engine
speeds.
The Mitsubishi K3H developed 28 hp (20.9 kW) at 2,700 rpm, making it
suitable for light to moderate agricultural tasks and construction
equipment operation. The engine features a cast iron cylinder block, an
overhead valve (OHV) valvetrain with two valves per cylinder, and a
mechanical direct injection fuel system. The K3H became a preferred
powerplant for the Mitsubishi MT250 and MT280D compact tractors, as well
as mini excavators in the agricultural and construction sectors. Known
for its economical operation and straightforward serviceability, the K3H
remains active in aftermarket parts supply and equipment restoration.
Engine Code: K3H
Engine Family: Mitsubishi K-series
Configuration: Inline 3-cylinder
Cycle: 4-cycle diesel
Valvetrain: Overhead Valve (OHV), 6 valves (2 per cylinder)
Displacement: 1.290 liters (1,290 cc; 78.7 cu.in)
Bore: 78.0 mm (3.07 in)
Stroke: 90.0 mm (3.54 in)
Firing Order: 1-3-2
Aspiration: Naturally aspirated
Fuel System: Mechanical direct injection
Injection Timing: 21° BTDC
Maximum Power: 28 hp (21 kW; 28.4 PS) at 2700 rpm
Idle Speed: 850-950 rpm (standard diesel operating range)
Set Speed Range: 2850-3150 rpm (K3H-11, K3H-12 variants)
The cylinder block is constructed from cast iron, providing the
structural rigidity, vibration damping, and thermal mass required for
sustained diesel operation in agricultural and construction
environments. The block features a vertical, in-line 3-cylinder
configuration with a deep-skirt design.
The cylinder bores are machined directly into the cast iron casting;
this engine does not use removable liners in its standard configuration.
The crankshaft is supported by four main bearings. Connecting rods are
forged steel. Pistons are aluminum alloy with a combustion bowl
optimized for the direct injection spray pattern. The engine includes
piston cooling features appropriate for naturally aspirated diesel
operation.
The cylinder head is manufactured from cast iron, ensuring uniform
thermal expansion with the cylinder block and providing a robust sealing
surface for the head gasket under diesel compression pressures. The
valve arrangement is overhead valve (OHV) with two valves per cylinder -
one intake and one exhaust - actuated by pushrods from a camshaft
located within the cylinder block. The valvetrain incorporates
mechanical lash adjusters, requiring periodic valve clearance inspection
and manual adjustment.
Valve seats are precision-machined and reinforced to withstand diesel
combustion pressures, with integrated cooling channels circulating
coolant to manage high temperatures under heavy-duty operations. Valve
clearance (cold) is 0.25 mm (0.0098 in) for both intake and exhaust
valves. The combustion chamber is a direct injection design, with the
piston bowl forming the majority of the combustion volume.
The fuel system employs mechanical direct injection with an in-line
injection pump. The pump is mounted to the side of the cylinder block
and is driven from the front gear train. The injection timing is set at
21° BTDC. The injectors are mechanical, spring-loaded, multi-hole
nozzles that open when fuel pressure overcomes spring preload.
A mechanical centrifugal governor controls fuel delivery based on engine
speed and load demand. A manual shut-off lever stops the engine by
cutting fuel supply. The system includes a fuel filter with a water
separator between the fuel tank and injection pump. A mechanical
hand-priming lever assists in bleeding air after filter changes.
The lubrication system is a pressurized, full-flow wet-sump design
utilizing a gear-type oil pump driven from the crankshaft. The oil pump
draws fluid from a cast iron oil pan. A full-flow spin-on oil filter is
mounted to the cylinder block. Recommended oil viscosity is 15W-40
conforming to API CD, CE, CF-4, or higher diesel specifications. Oil
pressure specification at rated speed is 35-50 psi (2.4-3.4 bar).
The cooling system is a pressure-controlled, thermostatically regulated
water-cooled arrangement with a belt-driven centrifugal water pump.
Coolant circulates through the cast iron cylinder block and cylinder
head.
A wax-element thermostat, with an opening temperature of 71-82°C
(160-180°F), regulates coolant flow to the front-mounted radiator. A
0.7-0.9 bar (10-13 psi) radiator cap maintains system pressure. The
system uses an ethylene glycol-based diesel coolant.
Intake System: The intake system includes a dry-type pleated paper air
filter suitable for agricultural and construction environments. The
intake manifold distributes air to each cylinder.
Exhaust System: The exhaust manifold is constructed from cast iron with
a single outlet flange. A muffler is fitted for noise reduction.
Electrical System: The engine is equipped with a 12-volt starter motor
and alternator. Glow plugs are installed for cold-start assistance.
Starting System: A key-operated starter switch engages the starter
motor. Glow plugs are pre-heated before starting in cold conditions.
Governor System: The mechanical centrifugal governor within the
injection pump maintains engine speed under varying loads, calibrated
for agricultural equipment operation.
Overall Length: 646 mm (25.4 in)
Overall Width: 564 mm (22.2 in)
Overall Height: 682 mm (26.9 in)
Dry Weight (engine only): 112 kg (247 lb)
Dry Weight (with flywheel and manifolds): 120 kg (265 lb)
Engine Oil Capacity (with filter change): 5.5-6.0 liters (5.8-6.3 qt)
Engine Oil Specification: 15W-40, API CD, CE, CF-4, or higher diesel oil
Oil Change Interval: 150 hours (severe duty) or 300 hours (normal duty)
Coolant Capacity (engine only): 3.5-4.0 liters (3.7-4.2 qt)
Coolant Specification: Ethylene glycol-based diesel coolant
Coolant Change Interval: 1,000 hours or 24 months
Thermostat Opening Temperature: 71-82°C (160-180°F)
Valve Clearance (cold, intake): 0.25 mm (0.0098 in)
Valve Clearance (cold, exhaust): 0.25 mm (0.0098 in)
Valve Clearance Adjustment Interval: 500 hours
Fuel Filter Replacement Interval: 500 hours
Air Filter Replacement Interval: Clean every 250 hours; replace as
required
Drive Belt Tension: Deflection of 10-12 mm (0.39-0.47 in) under 10 kg
(22 lb) force
Injection Timing: 21° BTDC
Injector Service Interval: Inspect spray pattern and opening pressure
every 1,000 hours
Cylinder Head Bolts (M14 main bolts): 147-157 Nm (108.4-115.7 lb-ft)
Cylinder Head Bolts (M14 tappet side bolts): 98-108 Nm (72.3-79.5 lb-ft)
Connecting Rod Cap Nuts: 54-63 Nm (39.8-46.3 lb-ft)
Intake Manifold Bolts: 22-28 Nm (16-21 lb-ft)
Exhaust Manifold Nuts: 18-25 Nm (13-18 lb-ft)
Injector Hold-Down Clamp Screws: 22-25 Nm (16-18 lb-ft)
Glow Plugs: 15-20 Nm (11-15 lb-ft)
Oil Pan Bolts: 10-12 Nm (7-9 lb-ft)
Water Pump Bolts: 20-25 Nm (15-18 lb-ft)
Oil Filter (spin-on): 15 Nm (11 lb-ft)
Starter Motor Mounting Bolts: 30-35 Nm (22-26 lb-ft)
Mitsubishi MT250 Compact Tractor: The K3H engine served as the
powerplant for the MT250, a compact utility tractor designed for
small-scale agricultural operations. The engine’s torque characteristics
suited light to moderate farming tasks including mowing, tilling, and
material handling.
Mitsubishi MT280D Compact Tractor (1984-1991): The K3H was the standard
engine for the MT280D, producing 28 hp at 2,700 rpm. This tractor was
equipped with a 9-forward, 3-reverse synchronized transmission and
featured a liquid-cooled 3-cylinder design enhancing efficiency and
longevity. The compact footprint allowed enhanced maneuverability in
tight spaces for small-scale operations and hobby farming.
Mini Excavators and Construction Equipment: The K3H engine is installed
in mini excavators and small construction machinery, particularly in
Mitsubishi-branded equipment. The diesel engine configuration provides
higher torque than equivalent gasoline engines, beneficial for
navigating varied terrain conditions. Engine components including
cylinder heads remain available for excavator applications.
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