Mitsubishi S6S Specifications
| Engine Model: Mitsubishi S6S |
| Engine Type: 4-cycle inline 6-cylinder naturally aspirated liquid-cooled diesel |
| Total Displacement: 304.9 cu.in (4.99 L) |
| Rated Engine Power: 88.5 Hp (66 kW) at 2500 rpm |
| Fuel System Type: Direct fuel injection |
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The Mitsubishi S6S is a substantial,
six-cylinder inline diesel engine designed for dependable, long-term
service in demanding industrial and construction applications. This
4.996-liter, naturally aspirated power plant delivers smooth, consistent
power through a direct injection combustion system, favoring low-end
torque and fuel efficiency. Its six-cylinder configuration provides
inherent mechanical balance, resulting in minimal vibration and smooth
operation across the entire speed range, a characteristic beneficial for
both operator comfort in machinery and stable power output in generator
sets.
The engine is constructed with a heavy-duty cast iron block and a
gear-driven camshaft, emphasizing durability and simplified maintenance
over high specific output. It serves as a core power source for
medium-sized excavators, large forklifts, and industrial generators
where reliable, continuous-duty performance is more critical than
maximum Hp.
Manufacturer: Mitsubishi Heavy Industries, Ltd.
Engine Model: S6S.
Engine Type: 4-cycle, water-cooled, vertical inline, direct injection
diesel.
Aspiration: Naturally aspirated.
Emission Compliance: Manufactured in configurations conforming to
historical industrial standards such as US EPA Tier 1 or equivalent
pre-regulation stages.
Management System: Mechanical fuel injection with mechanical governor.
Number of Cylinders: 6.
Bore: 94 mm (3.701 in).
Stroke: 120 mm (4.724 in).
Displacement: 4.996 L (4996 cc) (304.9 cu in).
Compression Ratio: 17.5:1.
Firing Order: 1-5-3-6-2-4.
Rotation Direction: Counter-clockwise when viewed from the flywheel
side.
Maximum Gross Power Output: 66 kW (88.5 hp) at 2,500 rpm.
Maximum Gross Torque: 278 Nm (205 lb-ft) at 1,600 rpm.
Rated Speed: 2,500 rpm for variable-speed applications; 1,500 or 1,800
rpm for constant-speed generator duty. Idle Speed: 650-750 rpm.
The cylinder block is a large, massively ribbed casting manufactured
from high-strength gray iron. It employs a deep-skirt design that
extends substantially below the crankshaft centerline, providing an
exceptionally rigid foundation that minimizes block flex and vibration.
The cylinder bores are precision-honed directly into the block material,
a linerless construction that ensures efficient heat transfer from the
cylinder walls to the surrounding coolant jackets.
The crankshaft is a forged steel component, supported by seven main
bearings. This seven-bearing support system is essential for maintaining
precise alignment and stability of the long crankshaft under load,
ensuring smooth rotation and extended bearing life. Connecting rods are
forged steel, fitted with replaceable precision bearing shells at the
crankpin end. The piston pin is a press-fit in the connecting rod small
end.
Pistons are aluminum alloy, designed with a specific re-entrant
combustion bowl to generate the necessary air swirl for efficient
combustion in the direct injection system. The piston ring pack consists
of two chrome-plated compression rings and a three-piece oil control
ring.
A single-piece cast iron cylinder head is utilized, secured to the block
with multiple high-tensile studs and nuts per cylinder. The head is
designed to accommodate one intake and one exhaust valve per cylinder.
Valve seat inserts are manufactured from hardened, heat-resistant alloy
to ensure durability. The valve train operates on an overhead valve
(OHV) principle, with the camshaft positioned in the cylinder block.
The camshaft is gear-driven from the crankshaft, providing positive,
maintenance-free timing. The camshaft actuates the valves via solid
pushrods and rocker arms. Rocker arms are mounted on a stationary shaft
fastened to the cylinder head. Valve clearance is set and maintained by
a screw and locknut adjustment on each rocker arm, a scheduled
maintenance task. The cylinder head is configured for direct injection,
with the fuel injector mounted centrally above each piston.
The engine employs a mechanical, inline pump-line-nozzle fuel injection
system. Core components include a mechanical fuel lift pump, a
six-element inline injection pump, high-pressure fuel lines, and
multi-hole pintle injectors. The injection pump is a large jerk-pump
design, driven by the engine's gear train. It supplies fuel at high
pressure directly into the main combustion chamber within the piston
bowl.
A mechanical centrifugal governor, integral to the injection pump,
regulates engine speed by controlling the position of the fuel rack. The
injection timing and fuel delivery curve are mechanically calibrated.
Fuel filtration involves a primary sedimentor/water separator and a
secondary fine filter, both critical for protecting the precision
components of the injection system.
Lubrication is provided by a high-capacity, forced-feed, full-flow wet
sump system. A gear-type oil pump, driven directly from the crankshaft,
draws oil from the sump through a large pickup tube equipped with a
strainer screen. Pressurized oil is routed through a full-flow, spin-on
cartridge oil filter. After filtration, oil enters the main oil gallery
in the block, supplying the crankshaft main and connecting rod bearings,
the camshaft bearings, and the valve gear via internal passages and
hollow pushrods.
The system is designed for high volume and pressure to ensure adequate
lubrication and cooling of all internal bearings across the long
cylinder block. The specified engine oil is API CD or CF grade. Total
oil capacity, including the filter, is 12.5 liters (13.2 US qt). The oil
pan is a heavy-duty stamped steel or cast iron component.
Cooling is managed by a pressurized, pump-circulated liquid system. A
centrifugal water pump, driven by a V-belt from the crankshaft pulley,
provides coolant circulation. System operating temperature is regulated
by a wax-pellet type thermostat. Heat rejection occurs via a substantial
tube-and-fin radiator; the cooling fan is mounted on the engine and is
V-belt driven.
The large displacement and six-cylinder format generate significant
heat, necessitating a high-capacity cooling system. The cooling system
requires a mixture of ethylene-glycol antifreeze and clean, deionized
water, generally in a 50/50 ratio. Total cooling system capacity is 15.0
liters (15.9 US qt) for the engine side, excluding the radiator and
external hose volume.
Intake System: Consists of an air cleaner and an intake manifold.
Exhaust System: Comprises an exhaust manifold and downpipe connecting to
the machine's exhaust silencer.
Electrical System: Operates on a 12V system. A 12V, 3.0 kW starter motor
and a 12V alternator (commonly 50-70A) are standard. The engine may
incorporate an intake manifold heater or glow plugs for cold starting
assistance, depending on the specific variant. An electric stop solenoid
acts on the injection pump rack.
Governor: A mechanical centrifugal governor is standard. Generator set
versions employ an isochronous mechanical governor or an electronic
speed controller for precise frequency regulation.
Length (Front Face of Block to Flywheel Housing): 1,033 mm (40.67 in).
Width (Overall): 593 mm (23.35 in).
Height (Overall, from sump to valve cover): 748 mm (29.45 in).
Dry Weight (with standard accessories): 345 kg (761 lb).
Engine Oil Change: Every 250 operating hours. Oil Filter Replacement:
Every oil change (250 hours). Fuel Filter Replacement: Replace primary
and secondary filter elements every 500 operating hours. Air Cleaner
Element Service: Clean or replace based on restriction indicator;
inspect regularly. Valve Clearance Adjustment: Check and adjust every
500 operating hours.
Coolant Replacement: Drain, flush, and refill every 2,000 operating
hours or every two years. Fan Belt Tension Check/Adjustment: Inspect and
adjust tension every 250 hours; replace at signs of wear. Fuel Injection
System Inspection: Have injection pressure and spray pattern checked by
a specialist every 1,500 hours.
Cylinder Head Nuts: Tighten in the specified multi-step crisscross
sequence to a final torque of 137-147 Nm (101-108 lb-ft).
Main Bearing Cap Bolts: 118-127 Nm (87-94 lb-ft).
Connecting Rod Cap Bolts: 78-88 Nm (58-65 lb-ft).
Flywheel to Crankshaft Bolts: 137-147 Nm (101-108 lb-ft).
Fuel Injector Holder: 69-78 Nm (51-58 lb-ft).
Oil Pan Drain Plug: 59-69 Nm (44-51 lb-ft).
Oil Filter Cartridge: Hand-tighten plus 3/4 turn after gasket contact.
The Mitsubishi S6S engine is found in a range of medium-duty industrial
and construction equipment where its smooth, torquey, and reliable
character is valued. Common applications include: Hydraulic Excavators:
Hyundai Robex R160LC-3, R170LC-3, R180LC-3. Forklift Trucks:
Large-capacity, heavy-duty forklifts and container handlers from
Mitsubishi, Caterpillar, and Komatsu in the 10-18 ton range.
Generator Sets: Industrial and prime power generator sets in the 45-60
kVA power range. Air Compressors: Large industrial stationary and
portable screw-type air compressors. Pumping Equipment: High-volume
water pumps for mining, dewatering, and irrigation. Agricultural
Machinery: Powers large agricultural tractors and combine harvesters in
certain markets. Marine Applications: Used as a propulsion engine for
small tugs, fishing vessels, and as an auxiliary generator drive.
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