Mitsubishi L3A Specifications
| Engine Model: Mitsubishi L3A |
| Engine Type: 4-cycle inline 3-cylinder naturally aspirated liquid-cooled diesel |
| Total Displacement: 42.5 cu.in (0.69 L) |
| Rated Engine Power: 17 Hp (13 kW) at 2700 rpm |
| Fuel System Type: Indirect injection |
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The Mitsubishi L3A is a compact, vertical,
water-cooled three-cylinder diesel engine from the Mitsubishi L-Series.
Produced from the mid-1970s through the late 1980s, this power unit was
engineered for small agricultural machinery, garden tractors, and light
industrial equipment where fuel efficiency, reliability, and compact
dimensions were required. The L3A uses an indirect injection combustion
system with a swirl chamber, a design that provides smooth operation and
good cold-start performance at the expense of some fuel economy compared
to direct injection engines.
The engine features a cast iron cylinder block, an aluminum alloy
cylinder head, and a naturally aspirated induction system. With a
displacement of 696 cc and power output of approximately 17 hp at 2,700
rpm, the L3A found its most recognized application in the Bolens
DGT-1700 garden tractor. The engine’s simple construction, mechanical
fuel system, and accessible service points made it suitable for
owner-maintained equipment in agricultural and residential settings.
The Mitsubishi L3A is a four-stroke, water-cooled, inline-three diesel
engine with a total displacement of 696 cc (0.696 L / 42.5 cu.in). The
bore and stroke dimensions are 65 mm (2.56 in) and 70 mm (2.76 in),
respectively, creating an undersquare configuration that emphasizes
low-speed torque production. The valvetrain employs an overhead valve
(OHV) design with two valves per cylinder - one intake and one exhaust -
for a total of six valves. The camshaft is positioned within the
cylinder block and actuates the valves through pushrods and rocker arms.
The combustion system uses indirect injection with a swirl chamber type
pre-combustion chamber. Induction is naturally aspirated through a cast
iron intake manifold. The fuel system is mechanical, utilizing an
in-line injection pump with a mechanical governor. The compression ratio
is set at a value suitable for indirect injection operation, with the
swirl chamber providing air motion for fuel-air mixing. Maximum power is
13 kW (17 hp) at 2,700 rpm. Peak torque is produced at a lower engine
speed, with the exact value varying by governor calibration. The engine
speed range for continuous operation is from idle to rated speed. The
firing order is 1-2-3, the standard arrangement for inline-three
engines.
The cylinder block is constructed from cast iron, a material selected
for its rigidity, wear resistance, and ability to withstand diesel
combustion loads. The inline-three configuration incorporates four main
bearings supporting a forged steel or cast iron crankshaft. The
crankshaft is counterweighted to balance the reciprocating forces of the
three-cylinder design. The connecting rods are constructed from forged
steel or sintered metal depending on the production year.
The cylinder bores are machined directly into the cast iron block
without removable liners. A plateau honed finish optimizes oil retention
and piston ring sealing. The water jacket surrounds the cylinders for
effective heat transfer, with coolant flow directed upward toward the
cylinder head. The block incorporates a deep-skirt design to enhance
structural stiffness. Cast-in mounting feet provide attachment points
for the equipment frame. The timing gear housing is integrated into the
front of the block, housing the gear train that drives the camshaft and
injection pump.
The cylinder head is manufactured from aluminum alloy, providing reduced
mass and enhanced heat dissipation compared to ferrous alternatives. The
overhead valve (OHV) arrangement positions the camshaft within the
block, with valve actuation provided by pushrods and rocker arms. The
rocker arms pivot on a rocker shaft mounted to the cylinder head and are
adjustable to set valve clearance.
Valves are arranged in-line along the cylinder head axis, with each
cylinder served by one intake valve and one exhaust valve. The indirect
injection system incorporates a swirl chamber for each cylinder,
machined into the cylinder head. This swirl chamber generates rotational
air motion during the compression stroke, promoting thorough mixing of
fuel and air before combustion begins - a feature that provides smooth,
quiet operation at the expense of some thermal efficiency.
Valve seat inserts are pressed into the cylinder head and machined to
precise angles. The valve springs are of the single-coil type. The
cylinder head gasket is a composite or steel design, providing reliable
sealing between the aluminum head and cast iron block.
The fuel system is a mechanical indirect injection system utilizing an
in-line injection pump mounted to the cylinder block and driven by the
timing gear train. Each cylinder has its own pump element (plunger and
barrel), delivering high-pressure fuel through steel lines to the
injection nozzles. A mechanical governor integrated into the injection
pump maintains engine speed under varying loads, automatically adjusting
fuel delivery to hold the set speed selected by the operator.
The injection nozzles are of the pintle type, positioned within each
swirl chamber. The nozzles are selected for the indirect injection
system, providing a spray pattern suited to the swirl chamber geometry.
A feed pump, integral to the injection pump, draws fuel from the
equipment-mounted tank through a fuel filter. A manual primer lever on
the feed pump allows bleeding of air from the system after filter
replacement.
The injection timing is mechanically fixed but adjustable by shimming
the pump mounting flange or rotating the pump housing. The maximum
injection pressure is lower than that of direct injection systems,
reflecting the indirect injection combustion principle.
The lubrication system is a full-pressure, full-flow circuit utilizing a
gear-type oil pump mounted within the timing gear case. The pump draws
engine oil from a cast aluminum or steel sump through a strainer screen
before directing it through a spin-on full-flow oil filter. An oil
pressure relief valve maintains system pressure within the specified
range. The main oil gallery distributes pressurized oil to the
crankshaft main bearings, connecting rod bearings, camshaft bearings,
and rocker arm assemblies.
The timing gears are lubricated by splash oil. The total engine oil
capacity, including the filter, is 2.5 L (2.6 qt) to 3.0 L (3.2 qt)
depending on the oil pan configuration. Recommended oil viscosity is SAE
10W-30 with a diesel rating of API Class CD or higher. SAE 30 mono-grade
oil is acceptable in warm ambient temperatures.
The cooling system is a thermostatically controlled water circulation
circuit designed for the compact dimensions of the L3A. A belt-driven
centrifugal water pump, mounted to the front of the cylinder block,
circulates a mixture of water and ethylene glycol antifreeze through the
cylinder block, cylinder head, and the radiator. The thermostat is a
wax-pellet type positioned on the coolant outlet of the cylinder head,
maintaining engine operating temperature within the range of 80°C to
90°C (176°F to 194°F).
The radiator is a vertical-core construction sized to the equipment
application. An engine-driven fan, mounted on the water pump pulley,
provides cooling airflow. An expansion or overflow tank allows for
coolant expansion. The total cooling system capacity varies by equipment
configuration but is 3.0 L (3.2 qt) to 4.0 L (4.2 qt).
| Intake and Exhaust Systems |
Intake System: The intake manifold is constructed from cast iron. The
naturally aspirated induction system draws air through a dry-type paper
air filter housed in a metal or plastic air cleaner assembly. An intake
silencer reduces induction noise. A flame arrestor is not required for
this industrial application.
Exhaust System: The exhaust manifold is constructed from cast iron,
mounting to the side of the cylinder head. The manifold collects exhaust
gases from all three cylinders and directs them to a single outlet for
connection to the equipment’s muffler and exhaust pipe. Back pressure
must be maintained within specified limits for proper engine operation.
Electrical System: The electrical system operates on 12 volts with a
small-capacity alternator or generator depending on the equipment. A
starter motor provides cranking power. Glow plugs are installed in each
swirl chamber for cold-start assistance, with glow duration controlled
by a manual switch or automatic timer. The glow plug system is essential
for reliable starting at ambient temperatures below 10°C (50°F).
Timing Drive: The camshaft and injection pump are driven by a gear train
from the crankshaft. This gear drive system eliminates the need for
timing belt or chain replacements, contributing to the engine’s
simplicity and long service life. Accessory drives for the water pump
and alternator are belt-driven from the crankshaft pulley.
The overall length, measured from the front pulley to the flywheel
housing face, is 500 mm (19.7 in). Width across the cylinder head and
injection pump is 450 mm (17.7 in). Height from the bottom of the oil
sump to the top of the cylinder head cover is 600 mm (23.6 in). The dry
weight of the engine, inclusive of the intake and exhaust manifolds,
injection pump, starter, alternator, and flywheel but without
transmission or fluids, is 90 kg (198 lb).
The Mitsubishi L3A requires regular maintenance aligned with small
engine service intervals. The engine oil and filter must be replaced
after the first 50 hours of operation (break-in), then every 100
operating hours or annually, whichever comes first. The oil filter
requires replacement every 200 operating hours, with the initial
break-in change at 50 hours.
The oil capacity is 2.5 L (2.6 qt) to 3.0 L (3.2 qt). The fuel filter
requires replacement every 200 operating hours or as indicated by
reduced engine performance. The air filter element should be inspected
at each oil change and replaced when dirty. Valve clearance adjustment
is required at intervals of 200 operating hours, with cold clearances of
0.25 mm (0.010 in) for both intake and exhaust valves.
The cooling system requires periodic flushing and coolant replacement
every 500 operating hours or 12 months. The glow plugs should be tested
before each cold season and replaced if resistance values deviate from
specification. The injection pump timing should be checked at major
overhaul intervals.
Cylinder Head Bolts (M10 / Large): 73.5 to 83.4 Nm (54.3 to 61.5 lb-ft).
Cylinder Head Bolts (M8 / Small): 19.6 to 29.4 Nm (14.5 to 21.7 lb-ft).
Main Bearing Cap Bolts: 50 to 60 Nm (37 to 44 lb-ft).
Connecting Rod Cap Nuts: 48.8 to 54.2 Nm (36.0 to 40.0 lb-ft).
Rocker Arm Shaft Bracket Bolts: 20 to 25 Nm (15 to 18 lb-ft).
Rocker Arm Adjustment Locknuts: 10 to 15 Nm (7 to 11 lb-ft).
Flywheel Bolts: 45 to 55 Nm (33 to 41 lb-ft).
Crankshaft Pulley Bolt: 80 to 100 Nm (59 to 74 lb-ft).
Intake Manifold Bolts: 15 to 20 Nm (11 to 15 lb-ft).
Exhaust Manifold Nuts: 18 to 25 Nm (13 to 18 lb-ft).
Injection Pump Mounting Nuts: 20 to 25 Nm (15 to 18 lb-ft).
Injector Holders: 50 to 60 Nm (37 to 44 lb-ft).
Oil Pan Bolts: 10 to 15 Nm (7 to 11 lb-ft).
Glow Plugs: 10 to 15 Nm (7 to 11 lb-ft).
The Mitsubishi L3A engine was deployed primarily in small agricultural
and industrial equipment, with limited on-road applications.
Bolens DGT-1700 Garden Tractor: The L3A was the factory-installed diesel
engine in the Bolens DGT-1700, a heavy-duty garden tractor produced in
the early 1980s. This application represented the most recognized use of
the L3A in the North American market, mated to a hydrostatic
transmission and used for mowing, tilling, and snow removal.
Mitsubishi Farm Machinery: The L3A was installed in various
Mitsubishi-branded agricultural machines for the Japanese domestic
market, including small tillers, compact tractors, and power carts.
These applications utilized the engine’s compact dimensions and low fuel
consumption for small-scale farming operations.
Industrial Power Units: The L3A was sold as a stationary power unit for
pumps, generators, and small compressors. These applications used a
radiator cooling package matched to the specific installation.
Compact Construction Equipment: Some small construction equipment,
including compaction rollers and small trenching machines, utilized the
L3A as their power source. Service intervals for these applications
followed engine operating hours rather than distance traveled.
Production of the L3A ceased in the late 1980s, with later L-Series
engines offering increased displacement and direct injection combustion.
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