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Yanmar 2V78 Engine

The Yanmar 2V78 is a heavy-duty, twin-cylinder, liquid-cooled, four-stroke diesel engine engineered for industrial, agricultural, and commercial applications. Built with a V-twin configuration, this compact power unit is designed to deliver reliable torque output, exceptional thermal efficiency, and low vibration levels. Its robust cast-iron block design ensures structural integrity under continuous, high-load operations, making it a common choice for utility vehicles, small tractors, generators, and specialized industrial machinery.

The engine features an overhead valve design driven by a high-strength camshaft located within the cylinder block. It utilizes a mechanical pushrod and rocker arm assembly to actuate two valves per cylinder. Valve clearance adjustments must be performed periodically using the standard locknut adjustments on the rocker arms to ensure proper sealing, accurate timing, and optimal volumetric efficiency. The cylinder bore is 78 mm, and the piston stroke is 78 mm. This symmetrical configuration minimizes lateral piston slap against the cylinder walls and reduces internal friction during high-RPM cycles.

The fuel system uses a highly precise, mechanical indirect injection configuration. It consists of a low-pressure feed pump that draws fuel from the tank through a primary fuel filter and water separator. The fuel is then delivered to an inline or cassette-type high-pressure injection pump. This pump times and methers fuel delivery through high-pressure steel lines to the throttle-type injection nozzles positioned within the pre-combustion chambers. Engine speed regulation is precisely managed by a mechanical centrifugal governor integrated into the gear train.

Engine lubrication is handled by a fully pressurized, wet-sump system. A high-efficiency trochoid oil pump, driven directly by the crankshaft, draws oil from the oil pan and forces it through a full-flow, replaceable spin-on oil filter cartridge. Pressurized oil channels distribute lubrication directly to the main bearings, connecting rod journals, and the upper valvetrain components. A mechanical pressure relief valve prevents over-pressurization during cold starts.

Thermal regulation is achieved via a closed-loop liquid cooling system. The system incorporates a centrifugal water pump driven by a V-belt, an engine-mounted radiator, a cooling fan, and a pellet-type thermostat. The thermostat remains closed during startup to allow the engine to rapidly reach its optimal operating temperature, then opens to route coolant through the radiator core, preventing overheating under continuous industrial loads.

General Technical Data

Engine Specifications

Engine Model ............... Yanmar 2V78
Engine Type ............... 4-cycle V-type 2-cylinder indirect injection liquid-cooled diesel
Number of Cylinders ............... 2
Cylinder Arrangement ............... 80-degree V-twin
Engine Bore, in (mm) ............... 3.07 (78.0)
Engine Stroke, in (mm) ............... 3.09 (78.4)
Displacement, cu.in (L) ............... 45.7 (0.749)
Rated Power, hp (kW) ............... 16.1-20.0 (12.0-14.9)
Rated Speed, rpm ............... 2800-3600
Peak Torque ............... 37.6 lb-ft (51.0 Nm) at 2250 rpm
High Idle Speed, rpm ............... 3250-3750
Low Idle Speed, rpm ............... 2475-2525
Aspiration Type ............... Naturally Aspirated
Compression Ratio ............... 23.0:1
Firing Order ............... 1-2
Direction of Rotation ............... Counterclockwise facing flywheel
Combustion System ............... Indirect injection swirl chamber type
Cylinder Block Material ............... Cast iron
Cylinder Head Material ............... Cast iron
Lubrication System ............... Full-pressure lubrication
Oil Pump Type ............... Trochoid gear pump
Oil Filter Type ............... Full-flow spin-on cartridge
Cooling System ............... Liquid-cooled centrifugal pump forced circulation
Water Pump Type ............... Belt-driven centrifugal
Air Cleaner Type ............... Dry dual-element cyclonic
Starting System ............... Electric motor starter
Electrical System ............... 12V
Charging System ............... Alternator 15A

Fuel System

Fuel Injection Pump Type ............... Yanmar in-line cassette pump type
Fuel Injection Nozzle Type ............... Throttle nozzle type
Fuel Injection Pressure, psi (MPa) ............... 1991-2132 (13.7-14.7)
Fuel Injection Timing, deg ............... 14-16 before top dead center
Fuel Transfer Pump Type ............... Electromagnetic plunger pump
Fuel Filter Type ............... Spin-on element with water separator cartridge
Governor Type ............... Mechanical centrifugal all-speed type
Governor Linkage Type ............... Spring-loaded sliding mechanical rack
Recommended Fuel Grade ............... ASTM D975 No. 2-D ultra low sulfur diesel
Fuel Return Line Type ............... Rubber hose to fuel reservoir
Maximum Fuel Pump Suction Head, in (mm) ............... 19.6 (500.0)
Maximum Fuel Return Backpressure, psi (kPa) ............... 1.45 (10.0)
Nozzle Valve Seat Angle, deg ............... 45
Injection Pump Plunger Diameter, in (mm) ............... 0.196 (5.0)
Injection Pump Plunger Stroke, in (mm) ............... 0.236 (6.0)

Dimensions and Weight

Overall Length, in (mm) ............... 19.1 (485)
Overall Width, in (mm) ............... 19.5 (495)
Overall Height, in (mm) ............... 20.8 (530)
Dry Weight, lbs (kg) ............... 113 (51)
Wet Weight, lbs (kg) ............... 124 (56)

Maintenance Data

Service Information

Minimum Compression Pressure, psi (MPa) ............... 426 (2.94)
Standard Compression Pressure, psi (MPa) ............... 497 (3.43)
Oil Pressure at Rated Speed, psi (MPa) ............... 42.6-56.8 (0.29-0.39)
Oil Pressure at Idle Speed, psi (MPa) ............... 14.2 (0.10)
Oil Temperature Standard Range, F (C) ............... 185-221 (85.0-105.0)
Standard Coolant Operating Temperature, F (C) ............... 167-194 (75.0-90.0)
Thermostat Valve Opening Temperature, F (C) ............... 160 (71.0)
Thermostat Full Open Temperature, F (C) ............... 185 (85.0)
Intake Valve Clearance (Cold), in (mm) ............... 0.0059-0.0078 (0.150-0.200)
Exhaust Valve Clearance (Cold), in (mm) ............... 0.0059-0.0078 (0.150-0.200)

Engine Oil and Coolant

Engine Oil Type .................. SAE 30, SAE 10W-30, or SAE 15W-40
API Service Classifications ......................... CD or higher
Engine Oil Capacity with Filter, qt (L) ............... 2.32 (2.2)
Engine Oil Capacity without Filter, qt (L) ............... 2.11 (2.0)
Cooling System Capacity, qt (L) ............... 1.58 (1.5)

Service Intervals

Change oil and filter ............... Every 200 hours
Inspect air cleaner ............... Every 50 hours
Replace air cleaner ............... Every 250 hours
Replace fuel filter ............... Every 200 hours
Valve clearance adjustment ............... Every 500 hours
Fuel system inspection ............... Every 1000 hours
Change coolant ............... Every 1000 hours
Compression test ............... Every 1000 hours
Clean radiator core ............... Every 200 hours
Inspect belt tension ............... Every 100 hours

Service Specifications

Cylinder Bore Inside Diameter, in (mm) ............... 3.0708-3.0712 (78.000-78.010)
Cylinder Bore Wear Limit Maximum, in (mm) ............... 3.0787 (78.200)
Cylinder Bore Out-of-Round Limit, in (mm) ............... 0.0004 (0.010)
Cylinder Block Upper Deck Surface Warpage Flatness, in (mm) ............... 0.0019 (0.050)
Main Bearing Journal Bore I.D, in (mm) ............... 1.8897-1.8903 (48.000-48.016)
Connecting Rod Small End Bushing I.D, in (mm) ............... 0.8665-0.8673 (22.010-22.030)
Connecting Rod Big End I.D, in (mm) ............... 1.6929-1.6933 (43.000-43.010)
Crankpin Standard Diameter, in (mm) ............... 1.5744-1.5748 (39.991-40.000)
Crankpin Bearing Clearance, in (mm) ............... 0.0011-0.0025 (0.030-0.064)
Connecting Rod Bearing Clearance, in (mm) ............... 0.0047 (0.120)
Connecting Rod Side Play, in (mm) ............... 0.0059-0.0137 (0.150-0.350)
Crankshaft Main Journal Diameter, in (mm) ............... 1.7318-1.7322 (43.991-44.000)
Crankshaft Main Bearing Clearance, in (mm) ............... 0.0011-0.0026 (0.030-0.068)
Crankshaft End Play, in (mm) ............... 0.0043-0.0082 (0.110-0.210)
Piston Skirt Outside Diameter, in (mm) ............... 3.0681-3.0689 (77.930-77.950)
Piston to Cylinder Wall Clearance, in (mm) ............... 0.0019-0.0031 (0.050-0.080)
Piston Pin Bore Inside Diameter, in (mm) ............... 0.8661-0.8665 (22.000-22.009)
Piston Pin Outside Diameter, in (mm) ............... 0.8657-0.8661 (21.989-22.000)
Piston Pin to Piston Pin Bore Clearance , in (mm) ............... 0.0000-0.0007 (0.000-0.020)
Top Ring Groove Width, in (mm) ............... 0.0602-0.0610 (1.530-1.550)
Second Ring Groove Width, in (mm) ............... 0.0602-0.0610 (1.530-1.550)
Oil Ring Groove Width, in (mm) ............... 0.1185-0.1193 (3.010-3.030)
Top Ring Side Clearance, in (mm) ............... 0.0024-0.0039 (0.060-0.100)
Second Ring Side Clearance, in (mm) ............... 0.0019-0.0035 (0.050-0.090)
Oil Ring Side Clearance, in (mm) ............... 0.0012-0.0028 (0.030-0.070)
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) ............... 0.0078-0.0157 (0.200-0.400)
Cylinder Head Bottom Surface Distortion Flatness, in (mm) ............... 0.0011 (0.030)
Intake Valve Stem Outside Diameter, in (mm) ............... 0.2346-0.2350 (5.960-5.970)
Exhaust Valve Stem Outside Diameter, in (mm) ............... 0.2340-0.2344 (5.945-5.955)
Intake Valve Guide Inside Diameter, in (mm) ............... 0.2362-0.2367 (6.000-6.012)
Exhaust Valve Guide Inside Diameter, in (mm) ............... 0.2362-0.2367 (6.000-6.012)
Intake Valve Stem-to-Guide Clearance, in (mm) ............... 0.0011-0.0020 (0.030-0.052)
Exhaust Valve Stem-to-Guide Clearance, in (mm) ............... 0.0017-0.0026 (0.045-0.067)
Intake Valve Seat Angle, deg ............... 45
Exhaust Valve Seat Angle, deg ............... 45
Intake Valve Face Angle, deg ............... 45
Exhaust Valve Face Angle, deg ............... 45
Intake Valve Sink Depth, in (mm) ............... 0.0157-0.0236 (0.400-0.600)
Exhaust Valve Sink Depth , in (mm) ............... 0.0157-0.0236 (0.400-0.600)
Valve Spring Free Length, in (mm) ............... 1.3937 (35.400)
Camshaft Main Journal Diameter, in (mm) ............... 1.4169-1.4173 (35.991-36.000)
Camshaft Journal Bearing Clearance, in (mm) ............... 0.0011-0.0029 (0.030-0.075)
Camshaft Cam Lobe Height (Intake), in (mm) ............... 1.2582-1.2614 (31.960-32.040)
Camshaft Cam Lobe Height (Exhaust), in (mm) ............... 1.2582-1.2614 (31.960-32.040)
Rocker Arm Shaft Outside Diameter, in (mm) ............... 0.4716-0.4720 (11.980-11.990)
Rocker Arm Bushing Inside Diameter, in (mm) ............... 0.4724-0.4732 (12.000-12.020)
Rocker Arm Shaft-to-Bushing Clearance, in (mm) ............... 0.0003-0.0015 (0.010-0.040)
Crankshaft Timing Gear to Camshaft Gear Backlash, in (mm) ............... 0.0027-0.0055 (0.070-0.140)
Camshaft Gear to Idler Gear Backlash, in (mm) ............... 0.0027-0.0055 (0.070-0.140)
Idler Gear to Oil Pump Gear Backlash, in (mm) ............... 0.0027-0.0055 (0.070-0.140)
Idler Gear to Oil Pump Gear Backlash, in (mm) ............... 0.0098 (0.250)

Tightening Torques

Cylinder Head Bolt, lb-ft (Nm) ............... 39.1-43.4 (53.0-59.0)
Connecting Rod Cap Bolt, lb-ft (Nm) ............... 17.4-20.2 (23.5-27.5)
Main Bearing Cap Bolt, lb-ft (Nm) ............... 39.1-43.4 (53.0-59.0)
Flywheel Mounting Bolt, lb-ft (Nm) ............... 57.8-65.1 (78.4-88.3)
Flywheel Housing Cap Screw, lb-ft (Nm) ............... 17.4-21.7 (23.5-29.4)
Crankshaft Pulley End Bolt, lb-ft (Nm) ............... 61.4-69.4 (83.3-94.1)
Camshaft Thrust Plate Bolt, lb-ft (Nm) ............... 6.5-8.7 (8.8-11.8)
Rocker Arm Shaft Support Bracket Bolt, lb-ft (Nm) ............... 6.5-8.7 (8.8-11.8)
Valve Cover Bonnet Bolt, lb-ft (Nm) ............... 5.1-7.2 (6.9-9.8)
Oil Pan Drain Plug, lb-ft (Nm) ............... 21.7-28.9 (29.4-39.2)
Oil Pan Mounting Bolt, lb-ft (Nm) ............... 5.1-7.2 (6.9-9.8)
Gear Case Front Cover Bolt, lb-ft (Nm) ............... 6.5-8.7 (8.8-11.8)
Gear Case Front Cover Bolt, lb-ft (Nm) ............... 17.4-21.7 (23.5-29.4)
Fuel Injection Pump Retaining Nut, lb-ft (Nm) ............... 5.1-7.2 (6.9-9.8)
Fuel Injection Pump Delivery Valve Holder, lb-ft (Nm) ............... 25.3-28.9 (34.3-39.2)
Fuel Injection Nozzle Case Nut, lb-ft (Nm) ............... 28.9-36.1 (39.2-49.0)
Fuel Injection Nozzle Holder Bolt, lb-ft (Nm) ............... 5.1-7.2 (6.9-9.8)
Fuel Injection Nozzle Holder Joint Nut, lb-ft (Nm) ............... 14.5-18.1 (19.6-24.5)
Fuel Return Line Joint Bolt, lb-ft (Nm) ............... 5.1-7.2 (6.9-9.8)
Fuel Pump Spill Timing Hole Plug, lb-ft (Nm) ............... 7.2-10.8 (9.8-14.7)
Exhaust Manifold Mounting Stud Nut, lb-ft (Nm) ............... 17.4-21.7 (23.5-29.4)
Intake Manifold Mounting Bolt, lb-ft (Nm) ............... 6.5-8.7 (8.8-11.8)
Starter Motor Mounting Bolt, lb-ft (Nm) ............... 17.4-21.7 (23.5-29.4)
Alternator Pivot Mount Bolt, lb-ft (Nm) ............... 14.5-18.1 (19.6-24.5)
Alternator Adjuster Link Tensioning Bolt, lb-ft (Nm) ............... 6.5-8.7 (8.8-11.8)
Oil Pressure Switch, lb-ft (Nm) ............... 7.2-10.8 (9.8-14.7)
Coolant Temperature Switch, lb-ft (Nm) ............... 14.5-21.7 (19.6-29.4)
Glow Plug Torque, lb-ft (Nm) ............... 5.8-8.7 (7.8-11.8)
Water Pump Assembly Mounting Bolt, lb-ft (Nm) ............... 6.5-8.7 (8.8-11.8)
Thermostat Housing Cover Bolt, lb-ft (Nm) ............... 6.5-8.7 (8.8-11.8)
Radiator Fan Mounting Bolt, lb-ft (Nm) ............... 5.1-7.2 (6.9-9.8)
Oil Pump Stator Base Cover Screw, lb-ft (Nm) ............... 4.3-6.5 (5.9-8.8)
Idler Shaft Plate Bolt, lb-ft (Nm) ............... 6.5-8.7 (8.8-11.8)
Oil Pressure Relief Valve Plug, lb-ft (Nm) ............... 17.4-23.1 (23.5-31.4)
Fuel Filter Bracket Wall Bolt, lb-ft (Nm) ............... 17.4-21.7 (23.5-29.4)
Air Cleaner Bracket Clamping Screw, lb-ft (Nm) ............... 5.1-7.2 (6.9-9.8)
Muffler Flange Attachment Stud Nut, lb-ft (Nm) ............... 17.4-21.7 (23.5-29.4)
Stop Solenoid Lock Nut, lb-ft (Nm) ............... 10.8-14.5 (14.7-19.6)

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