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Shibaura S773 Engine

The Shibaura S773 is a compact, heavy-duty industrial diesel engine widely utilized in commercial lawn mowers (such as Hustler Turf Equipment), sub-compact tractors, and utility machinery. Engineered as an in-line, multi-cylinder power plant, it is known for its high power-to-weight ratio, structural rigidity, and adherence to Tier 4 emissions standards. The design prioritizes overhead valve (OHV) mechanical simplicity, long service intervals, and reliable low-end torque delivery under demanding commercial operation cycles.

The engine employs a conventional Overhead Valve (OHV) pushrod configuration. It features two valves per cylinder (one intake, one exhaust) actuated by a single, gear-driven camshaft via solid mechanical lifters and rocker arms. Valve clearance adjustments are managed via adjusting screws on the rocker assembly and are scheduled for periodic service intervals. Bore: 77 mm (3.031 inches). Stroke: 72 mm (2.835 inches). Total Displacement: 1.0 Liters (1005 cc or 61.3 cu.in).

Fuel delivery is managed via a reliable, mechanical indirect injection system. It features a Bosch PFR inline injection pump timed directly to the engine's camshaft gear train. This high-pressure pump pushes diesel through steel lines to individual mechanical fuel injectors mounted in the cylinder head. Cold-start assist is provided by individual 12V electric glow plugs positioned inside the pre-combustion chambers, while an external electric fuel shutoff solenoid controls fuel metering to start and stop the engine.

Lubrication is managed by a forced-feed pressure system driven by a trochoid-type oil pump integrated into the gear case. The system pulls oil from a stamped steel oil pan through a full-flow, spin-on oil filter. The engine uses a forced-circulation liquid cooling system. Coolant flow is regulated by a belt-driven, centrifugal water pump and an inline wax-pellet thermostat that maintains optimal thermal efficiency. A pusher or puller fan cools the radiator core, and the factory spec demands a 50/50 ethylene glycol and water mixture to prevent cavitation and internal corrosion.

General Technical Data

Engine Specifications

Engine Model ............... Shibaura S773
Engine Type ............... 4-cycle vertical inline 3-cylinder liquid-cooled diesel
Number of Cylinders ............... 3
Cylinder Arrangement ............... In-line
Engine Bore, in (mm) ............... 3.031 (77.0)
Engine Stroke, in (mm) ............... 2.835 (72.0)
Total Displacement, cu.in (L) ............... 61.3 (1.005)
Rated Power, hp (kW) ............... 22.0 (16.4) at 3000 rpm
Minimum Power, hp (kW) ............... 14.0 (10.4) at 2400 rpm
Rated Speed, rpm ............... 3000
Max Governed Speed, rpm ............... 3000-3050
Low Idle Speed, rpm ............... 750-850
High Idle Speed, rpm ............... 3100-3200
Peak Torque, lb-ft (Nm) ............... 39.5 (53.6) at 1800 rpm
Aspiration Type ............... Naturally Aspirated
Combustion Type ............... Swirl chamber indirect injection
Compression Ratio ............... 22.5:1-23.0:1
Firing Order ............... 1-2-3
Rotation Direction ............... Counterclockwise from flywheel end
Cylinder Block Material ............... Cast iron
Cylinder Head Material ............... Cast iron
Number of Valves per Cylinder ............... 2
Total Number of Valves ............... 6
Intake Valve Arrangement ............... Overhead valve
Exhaust Valve Arrangement ............... Overhead valve
Lubrication System ............... Forced pressure circulation
Oil Pump Type ............... Trochoid rotor gear type
Oil Filter Type ............... Full-flow, spin-on cartridge
Cooling System ............... Forced liquid circulation with centrifugal pump
Water Pump Type ............... Belt-driven centrifugal impeller
Thermostat Type ............... Wax pellet element type
Air Cleaner Type ............... Dry element or oil bath type
Starting System ............... Electric starter motor
Electrical System ............... 12V
Alternator Capacity ............... 15A

Fuel System

Fuel Injection Pump Type ............... Bosch inline IDI type
Governor Type ............... Mechanical centrifugal all-speed governor
Fuel Injection Nozzle Type ............... Throttle type nozzle
Injection Timing, degrees ............... 18-20 before top dead center
Fuel Injection Pressure, psi (MPa) ............... 1700-1850 (11.7-12.7)
Fuel Transfer Pump Type ............... Mechanical diaphragm type
Fuel Filter Type ............... Spin-on cartridge with water sedimenter
Recommended Fuel Grade ............... SAE No.2-D, DIN 51601, BS Class A-1
Low Temperature Fuel Grade ............... SAE No.1-D winter formula fuel
Maximum Fuel Return Flow, gal/hr (L/hr) ............... 2.6 (10.0)
Fuel Feed Line Diameter, in (mm) ............... 0.23 (6.0)
Fuel Return Line Diameter, in (mm) ............... 0.19 (4.8)
Maximum Fuel Temperature at Pump Inlet, F (C) ............... 140 (60)
Injection Nozzle Valve Opening Pressure, psi (bar) ............... 1740 (120)
Fuel Tank Vent Requirement ............... Open atmosphere vent orifice

Dimensions and Weight

Overall Length, in (mm) ............... 18.9 (480)
Overall Width, in (mm) ............... 19.8 (505)
Overall Height, in (mm) ............... 21.9 (555)
Dry Weight, lbs (kg) ............... 181 (82)

Maintenance Data

Service Information

Oil Pressure at Low Idle, psi (kPa) ............... 14.5 (100.0)
Oil Pressure at Rated Speed, psi (kPa) ............... 43.5-58.0 (300.0-400.0)
Thermostat Opening Temperature, F (C) ............... 160 (71)
Thermostat Full Open Temperature, F (C) ............... 185 (85)
Cooling System Cap Pressure, psi (kPa) ............... 13.0 (90.0)
Alternator Belt Deflection Under 22 lb Force, in (mm) ............... 0.39-0.47 (10.0-12.0)
Intake Valve Clearance (Cold), in (mm) ............... 0.0080 (0.203)
Exhaust Valve Clearance (Cold), in (mm) ............... 0.0080 (0.203)

Engine Oil and Coolant

Engine Oil Type .................. SAE 30, SAE 10W, or 10W-30
API Service Classifications ......................... CD, CE, CF, CF-4, or CH-4
Engine Oil Capacity with Filter, qts (L) ............... 3.2 (3.0)
Engine Oil Capacity without Filter, qts (L) ............... 2.8 (2.6)
Cooling Capacity, Engine Only, qts (L) ............... 3.4 (3.2)
Cooling Capacity with Radiator, qts (L) ............... 4.4 (4.2)

Service Intervals

Change oil and filter ............... Every 200 hours
Inspect air cleaner ............... Every 50 hours
Replace air cleaner ............... Every 400 hours
Replace fuel filter ............... Every 200 hours
Valve clearance adjustment ............... Every 400 hours
Fuel system inspection ............... Every 600 hours
Change coolant ............... Every 1000 hours
Compression test ............... Every 1000 hours
Clean radiator core ............... Every 250 hours
Inspect belt tension ............... Every 100 hours

Service Specifications

Cylinder Bore Inner Diameter, in (mm) ............... 3.0315-3.0323 (77.000-77.019)
Cylinder Bore Roundness, in (mm) ............... 0.0004 (0.010)
Cylinder Block Top Surface Flatness, in (mm) ............... 0.0020 (0.050)
Cylinder Head Bottom Surface Flatness, in (mm) ............... 0.0020 (0.050)
Connecting Rod Small End Bushing I.D, in (mm) ............... 0.8271-0.8276 (21.008-21.020)
Connecting Rod Big End Side Axial Play, in (mm) ............... 0.0039-0.0118 (0.100-0.300)
Connecting Rod Bearing Clearance, in (mm) ............... 0.0014-0.0033 (0.035-0.083)
Crankshaft Main Journal Diameter, in (mm) ............... 2.0457-2.0463 (51.964-51.975)
Crankpin Journal Diameter, in (mm) ............... 1.6915-1.6921 (42.964-42.975)
Crankshaft Main Bearing Clearance, in (mm) ............... 0.0014-0.0034 (0.035-0.087)
Crankshaft End Play, in (mm) ............... 0.0020-0.0069 (0.050-0.175)
Piston Outer Diameter, in (mm) ............... 3.0295-3.0303 (76.950-76.969)
Piston to Cylinder Bore Clearance, in (mm) ............... 0.0012-0.0027 (0.031-0.069)
Piston Pin Bore Inner Diameter, in (mm) ............... 0.8268-0.8271 (21.000-21.009)
Piston Pin Outer Diameter, in (mm) ............... 0.8266-0.8268 (20.995-21.000)
Piston Pin to Piston Pin Bore Clearance, in (mm) ............... 0.0000-0.0006 (0.000-0.014)
Piston Pin to Con Rod Bushing Clearance, in (mm) ............... 0.0003-0.0010 (0.008-0.025)
Top Ring Groove Width, in (mm) ............... 0.0610-0.0622 (1.550-1.580)
Second Ring Groove Width, in (mm) ............... 0.0602-0.0614 (1.530-1.560)
Oil Ring Groove Width, in (mm) ............... 0.1189-0.1201 (3.020-3.040)
Top Ring Side Clearance, in (mm) ............... 0.0024-0.0039 (0.060-0.100)
Second Ring Side Clearance, in (mm) ............... 0.0020-0.0035 (0.050-0.090)
Oil Piston Ring Side Clearance, in (mm) ............... 0.0008-0.0024 (0.020-0.060)
Top Ring End Gap, in (mm) ............... 0.0059-0.0118 (0.150-0.300)
Second Ring End Gap, in (mm) ............... 0.0059-0.0118 (0.150-0.300)
Oil Ring End Gap, in (mm) ............... 0.0079-0.0157 (0.200-0.400)
Intake Valve Stem Outer Diameter, in (mm) ............... 0.2343-0.2348 (5.950-5.965)
Exhaust Valve Stem Outer Diameter, in (mm) ............... 0.2339-0.2344 (5.940-5.955)
Intake Valve Stem to Guide Clearance, in (mm) ............... 0.0012-0.0024 (0.030-0.060)
Exhaust Valve Stem to Guide Clearance, in (mm) ............... 0.0016-0.0028 (0.040-0.070)
Valve Guide Inner Diameter, in (mm) ............... 0.2358-0.2364 (5.990-6.010)
Intake Valve Margin Thickness, in (mm) ............... 0.0354-0.0394 (0.900-1.000)
Exhaust Valve Margin Thickness, in (mm) ............... 0.0354-0.0394 (0.900-1.000)
Intake Valve Seat Angle, degrees ............... 45
Exhaust Valve Seat Angle, degrees ............... 45
Intake Valve Face Angle, degrees ............... 45
Exhaust Valve Face Angle, degrees ............... 45
Valve Spring Free Length, in (mm) ............... 1.3780 (35.000)
Camshaft Journal Outer Diameter, in (mm) ............... 1.5724-1.5732 (39.940-39.960)
Camshaft Bearing Clearance, in (mm) ............... 0.0016-0.0036 (0.040-0.092)
Cam Lobe Height (Intake), in (mm) ............... 1.0425-1.0445 (26.480-26.530)
Cam Lobe Height (Exhaust), in (mm) ............... 1.0425-1.0445 (26.480-26.530)
Camshaft Axial End Play, in (mm) ............... 0.0020-0.0059 (0.050-0.150)
Rocker Arm Shaft Outer Diameter, in (mm) ............... 0.4713-0.4719 (11.973-11.984)
Rocker Arm Bushing Inner Diameter, in (mm) ............... 0.4724-0.4736 (12.000-12.030)
Rocker Arm Bushing to Shaft Clearance, in (mm) ............... 0.0006-0.0022 (0.016-0.057)
Idler Gear Shaft Outer Diameter, in (mm) ............... 0.9439-0.9445 (23.975-23.990)
Idler Gear Bushing Inner Diameter, in (mm) ............... 0.9449-0.9461 (24.000-24.025)
Idler Gear Bushing to Shaft Clearance, in (mm) ............... 0.0004-0.0020 (0.010-0.050)

Tightening Torques

Cylinder Head M10 Bolts, lb-ft (Nm) ............... 45.0 (61.0)
Cylinder Head M12 Bolts, lb-ft (Nm) ............... 70.1 (95.0)
Main Bearing Holder Support Cap, lb-ft (Nm) ............... 35.4-39.1 (48.0-53.0)
Main Bearing Holder Block Attachment Bolts, lb-ft (Nm) ............... 22.1 (30.0)
Connecting Rod Cap Nuts, lb-ft (Nm) ............... 18.5-19.9 (25.0-27.0)
Flywheel Retaining Bolts, lb-ft (Nm) ............... 41.3-50.9 (56.0-69.0)
Crankshaft Center Pulley Attachment Bolt, lb-ft (Nm) ............... 90.0-100.0 (122.0-135.0)
Crankshaft Rear Plate Fasteners, lb-ft (Nm) ............... 33.9-39.9 (46.0-54.0)
Rocker Arm Support Assembly Bolts, lb-ft (Nm) ............... 21.0-25.0 (28.0-34.0)
Valve Cover Retaining Cap Nuts, lb-ft (Nm) ............... 7.0-9.0 (9.5-12.0)
Timing Gear Case Cover Fasteners, lb-ft (Nm) ............... 14.0-18.0 (19.0-24.0)
Oil Pan Mounting Fasteners, lb-ft (Nm) ............... 7.0-9.0 (9.5-12.0)
Oil Pan Hexagonal Drain Plug Bolt, lb-ft (Nm) ............... 25.0-30.0 (34.0-41.0)
Fuel Injection Pump Intake Delivery Valves, lb-ft (Nm) ............... 29.0-33.0 (39.0-45.0)
Fuel Injection Pump High Pressure Line Nuts, lb-ft (Nm) ............... 18.0-22.0 (24.0-30.0)
Fuel Injection Nozzle Holder into Head, lb-ft (Nm) ............... 43.0-51.0 (59.0-69.0)
Fuel Nozzle Leak-Off Fuel Line Nut, lb-ft (Nm) ............... 18.0-22.0 (24.0-30.0)
Glow Plug Structural Body, lb-ft (Nm) ............... 11.0-15.0 (15.0-20.0)
Glow Plug Electrical Power Cable Terminal Nut, lb-ft (Nm) ............... 1.1-1.5 (1.5-2.0)
Thermostat Housing Attachment Flandge Bolts, lb-ft (Nm) ............... 14.0-18.0 (19.0-24.0)
Water Pump Assembly Flange Mounting Bolts, lb-ft (Nm) ............... 14.0-18.0 (19.0-24.0)
Water Temperature Gauge Sensor, lb-ft (Nm) ............... 18.0-22.0 (24.0-30.0)
Oil Pressure Sensor Indicator Switch, lb-ft (Nm) ............... 11.0-15.0 (15.0-20.0)
Exhaust Manifold Exhaust Fasteners, lb-ft (Nm) ............... 18.0-22.0 (24.0-30.0)
Intake Manifold Air Intake Bolts, lb-ft (Nm) ............... 14.0-18.0 (19.0-24.0)
Electric Starter Chassis Mounting Bolts, lb-ft (Nm) ............... 35.0-45.0 (47.0-61.0)
Alternator Pivoting Adjustment Bracket Bolt, lb-ft (Nm) ............... 14.0-18.0 (19.0-24.0)
Alternator Tension Lock Adjusting Bolt, lb-ft (Nm) ............... 9.0-13.0 (12.0-18.0)
Fan Pulley Drive Hub Assembly Nut, lb-ft (Nm) ............... 40.0-50.0 (54.0-68.0)

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