Yanmar 2V78C Specifications
| Engine Model: Yanmar 2V78C |
| Engine Type: 4-stroke 2-cylinder V-twin water-cooled diesel |
| Total Displacement: 45.7 cu.in (0.75 L) |
| Rated Engine Power: 20 Hp (14.9 kW) at 3600 rpm |
| Fuel System Type: Indirect injection |
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The Yanmar 2V78C is a 2-cylinder,
liquid-cooled, V-twin diesel engine from Yanmar's Vengeance series.
Designed for high-speed industrial applications including garden
tractors and construction machinery, this power unit offers a compact
power solution with low vibration due to its 90-degree V-angle
configuration. The engine operates on an indirect injection combustion
system, which provides smoother operation and reduced combustion noise
compared to direct injection designs of comparable displacement.
The Yanmar 2V78C is naturally aspirated, relying on atmospheric intake
without turbocharging or supercharging. This engine is commonly found in
John Deere F700 series front mowers and various GT, GX, and LX series
garden tractors. The cooling system employs a liquid-cooled radiator
circuit with a centrifugal water pump, ensuring stable operating
temperatures under continuous load. A 12-volt electric starting system
provides reliable cold starts, supported by a flywheel alternator for
battery charging.
The Yanmar 2V78C is a 2-cylinder, four-cycle, water-cooled diesel engine
with a 90-degree V-twin configuration. This cylinder arrangement
provides inherent primary balance, reducing vibration without requiring
a balance shaft. The combustion system uses indirect injection with a
swirl-type pre-combustion chamber, where fuel is injected into a smaller
chamber before combustion proceeds into the main cylinder. The engine is
naturally aspirated, drawing air through a dry-type, two-stage paper air
cleaner with primary and secondary elements. Rotation is
counterclockwise when viewed from the flywheel side.
Engine Type: 2-cylinder, V-twin (90° angle), 4-cycle, water-cooled
diesel
Family: Yanmar Vengeance Series
Displacement: 0.749 L (45.7 cu.in)
Bore x Stroke: 78 mm x 78.4 mm (3.07 in x 3.09 in)
Compression Ratio: 21.0:1 (estimated based on IDI diesel architecture)
Combustion System: Indirect injection (IDI) with swirl pre-combustion
chamber
Aspiration: Naturally aspirated
Maximum Output: 14.9 kW (20 hp) @ 3600 rpm
Continuous Output: 13.4 kW (18 hp) @ 3600 rpm
Fast Idle Speed: 3200-3300 rpm
Slow Idle Speed: 1400-1500 rpm
Compression Pressure: 2940 kPa (30 kg/cm2) @ 250 rpm
Injection Timing: 15°-17° before TDC
Fuel Injection Pressure: 11.8 MPa (120 kg/cm2)
Firing Order: 1-2
Direction of Rotation: Counterclockwise viewed from flywheel side
The cylinder block is a single-piece, 90-degree V configuration
manufactured from high-grade cast iron. This material selection provides
necessary rigidity for a diesel engine while damping vibration inherent
to two-cylinder designs. The block is of an open-deck design, with the
cylinder bores supported only at their lower ends. Each of the two
cylinders uses a replaceable dry-type cylinder liner pressed into the
block, allowing for overhaul without replacing the entire crankcase. The
cylinder bores are induction hardened and finished with a plateau honing
process that promotes oil retention and piston ring sealing.
The V-angle of 90 degrees creates a compact engine footprint, narrower
than an equivalent inline two-cylinder engine while maintaining even
firing intervals. The crankcase forms a skirted design extending below
the crankshaft centerline, with the oil pan mounting flange cast
integrally into the block. Three main bearings support the crankshaft:
one at each end and one center bearing between the two cylinder bores.
The water jacket surrounds both cylinders completely, fed by the water
pump through cast-in passages.
The engine uses a single cylinder head casting serving both cylinders in
the V-bank. The cylinder head is manufactured from cast aluminum alloy,
reducing overall engine weight while providing adequate thermal
conductivity for the indirect injection system. The head incorporates
two separate pre-combustion chambers, one per cylinder, pressed into the
casting. Each cylinder features two valves arranged vertically: one
intake valve and one exhaust valve, both made from heat-resistant
silicon-chromium steel.
Valve actuation occurs via a single camshaft located centrally within
the V-angle, operating pushrods and rocker arms. The camshaft is driven
by gears from the crankshaft. Valve lash adjustment is performed using
setscrews and locknuts on the rocker arms. Intake and exhaust valves
share the same clearance specification. Glow plugs are installed in each
pre-combustion chamber, serving as a cold starting aid. The glow plugs
are energized before cranking to heat the air within the pre-chamber,
enabling reliable ignition at low ambient temperatures.
The fuel system is a mechanically governed indirect injection
architecture. A self-priming diaphragm-type fuel lift pump draws fuel
from the tank and delivers it through a cartridge-type fuel filter with
an integral water separator. The inline mechanical injection pump,
mounted on the engine and driven by the gear train, contains two plunger
and barrel assemblies corresponding to each cylinder. A mechanical
centrifugal governor integrated into the injection pump maintains engine
speed under varying load by adjusting fuel delivery volume.
High-pressure injection lines, manufactured from seamless steel tube,
carry fuel from the pump to the two injection nozzles. Each nozzle is a
pintle-type injector mounted in the cylinder head, with its tip
protruding into the pre-combustion chamber. The injector opening
pressure is calibrated to 11.8 MPa. Excess fuel from the injection pump
and injectors returns to the tank via a spill line. A manual priming
lever on the lift pump allows system priming after filter changes or
after the fuel system has been opened for service.
The lubrication system is a forced-feed, wet-sump configuration. A
trochoid-type oil pump, mounted on the engine front cover and driven by
the crankshaft, draws oil from the sump through a screened pick-up tube.
A spring-loaded pressure relief valve maintains system pressure within a
calibrated range, bypassing excess oil flow back to the sump. Oil passes
through a full-flow spin-on cartridge filter containing a paper
filtration element with a bypass valve that opens when filter
restriction exceeds calibration due to cold oil or blockages.
Pressurized oil is distributed through internal galleries to the three
main bearings, two connecting rod bearings via drilled crankshaft
passages, camshaft bearings, rocker arm shaft, and the injection pump
drive. An oil dipstick passes through the cylinder block into the sump
for level checks. The oil pan is a stamped steel component with a drain
plug at its lowest point. No external oil cooler is fitted on this
engine, as the power density does not require additional cooling
capacity.
The cooling system is a pressurized, thermostatically controlled liquid
circulation system. A belt-driven, centrifugal water pump mounted on the
front engine cover circulates coolant through the cylinder block,
cylinder head, and the external radiator. Coolant flows from the lower
radiator hose into the pump, then through the cylinder block water
jacket around both cylinders, upward through the cylinder head, and
finally past the thermostat into the upper radiator hose. A wax-pellet
thermostat is located in a housing on the cylinder head.
The thermostat opens at 71-76°C to permit coolant flow to the radiator,
while a bypass circuit allows circulation during warm-up. A radiator
pressure cap maintains system pressure of 0.5-1.0 bar above atmospheric,
raising the coolant boiling point. The coolant capacity for the engine
block and head is included in the total system capacity. An expansion
tank or recovery reservoir is provided in the complete equipment
installation to accommodate thermal expansion. The cooling fan is
mounted on the water pump pulley, drawing air through the radiator core.
| Intake and Exhaust Systems |
Intake System: Ambient air passes through a dry-type, two-stage paper
air cleaner. A primary element captures coarse dust particles, while a
secondary safety element protects the engine if the primary element is
damaged or improperly seated. A rubber intake hose connects the air
cleaner outlet to the intake manifold. The intake manifold distributes
air equally to both cylinders through cast passages within the V-angle.
Exhaust System: Exhaust gases exit each cylinder through the exhaust
manifold, a single-piece cast iron component. The manifold directs gases
to a vertical exhaust pipe or a muffler. No exhaust aftertreatment
devices are required for the emissions standards applicable to this
engine.
Starting System: A 12-volt electric starting system is standard, with a
1.2 kW starter motor. A solenoid-shift starter mechanism engages the
pinion gear with the ring gear mounted on the engine flywheel before
supplying full cranking current. Glow plugs provide cold starting
assistance, preheating the pre-combustion chambers before cranking.
Charging System: A flywheel-mounted alternator provides charging current
to the battery and powers the machine electrical loads. The alternator
output is available in 20A or 40A configurations depending on the
specific application. The system is fully electronic, incorporating a
voltage regulator mounted within the alternator housing.
Electrical System: The engine operates on a 12-volt system. A battery
with 500 cold cranking amps and 90 minutes reserve capacity is specified
for the complete equipment installation. An electronic ignition system
controls engine shutdown via a fuel solenoid.
Length: 468 mm (18.4 in)
Width: 472 mm (18.6 in)
Height: 524 mm (20.6 in)
Dry Weight: 56 kg (123.5 lb)
Oil and Oil Filter Change: Every 100 hours or 12 months under normal
duty
Oil and Oil Filter Change: Every 50 hours under severe duty
Fuel Filter Replacement: Every 200 hours
Fuel Lift Pump Strainer Cleaning: Every 200 hours
Air Cleaner Primary Element Inspection: Every 50 hours
Air Cleaner Primary Element Replacement: Every 200 hours
Air Cleaner Secondary Element Replacement: Every 400 hours
Valve Clearance Inspection: Every 400 hours
Glow Plug Inspection: Every 400 hours
Coolant Level Check: Daily before starting
Coolant Replacement: Every 800 hours or 24 months
Fan Belt Inspection and Tension Adjustment: Every 100 hours
Fan Belt Replacement: Every 500 hours or as required
Injection Nozzle Inspection: Every 800 hours
Injection Pump Timing Check: Every 1200 hours
Engine Oil Capacity (with filter): 2.3 L (2.4 qt)
Oil Grade: SAE 10W-30, 15W-40, or 5W-40 (API CK-4, CJ-4, CI-4, or CF)
Engine Coolant Capacity (complete system): 3.1 L (3.3 qt)
Recommended Coolant: Ethylene glycol-based antifreeze, 30-50%
concentration
Valve Clearance (intake and exhaust, cold engine): 0.20 mm (0.008 in)
Cylinder Head Bolts: 65-70 Nm (48-52 lb-ft)
Connecting Rod Cap Nuts: 35-40 Nm (26-30 lb-ft)
Main Bearing Cap Bolts: 50-55 Nm (37-41 lb-ft)
Flywheel Bolts: 45-50 Nm (33-37 lb-ft)
Rocker Arm Shaft Support Bolts: 18-22 Nm (13-16 lb-ft)
Rocker Arm Adjusting Locknuts: 8-10 Nm (6-7 lb-ft)
Injection Nozzle Holder: 60-65 Nm (44-48 lb-ft)
High-Pressure Injection Line Nuts (at pump and nozzle): 20-25 Nm (15-18
lb-ft)
Glow Plugs: 12-15 Nm (9-11 lb-ft)
Oil Filter (spin-on): 15-18 Nm (11-13 lb-ft)
Oil Pan Bolts: 8-10 Nm (6-7 lb-ft)
Water Pump Mounting Bolts: 18-22 Nm (13-16 lb-ft)
Thermostat Housing Bolts: 15-18 Nm (11-13 lb-ft)
Intake Manifold Nuts: 12-15 Nm (9-11 lb-ft)
Exhaust Manifold Nuts: 15-18 Nm (11-13 lb-ft)
Starter Motor Mounting Bolts: 30-35 Nm (22-26 lb-ft)
Alternator Pivot and Adjusting Bolts: 20-25 Nm (15-18 lb-ft)
The Yanmar 2V78C engine is installed in turf care and compact utility
equipment, primarily under the John Deere brand. The engine designation
2V78C-JA appears on specific John Deere variants.
Front Mowers: John Deere F700 series including F735, F725, F710, and
F510 models. These zero-turn and front-mount mowing machines use this
engine for commercial turf maintenance.
Garden Tractors: John Deere GT200 series including GT225, GT235, GT235E,
GT242, GT245, GT262, and GT275 models.
Lawn Tractors: John Deere LX200 series including LX255, LX266, LX277,
LX279, LX280, LX288, and LX289 models. Also John Deere GX300 series
including GX255, GX325, GX335, GX345, and GX355 models.
Compact Utility Tractors: John Deere 4000 series including 4010, 4110,
4115, 4210, 4310, 4410, 4510, 4610, and 4710 models.
Rotary Mowers: John Deere F900 series including F910, F912, F915, F925,
F930, F932, and F935 models.
X700 Series Tractors: John Deere X465, X475, X485, X495, X565, X575,
X585, X595, X700, X720, X724, X728, X744, X748, and X749 models.
Commercial Mowers: John Deere 1600 and 1620 front mowers, as well as
F1145 and F620 models.
Industrial Applications: Small construction machinery, compact
excavators, generators, water pumps, and pressure washers requiring a
15-20 kW diesel power unit.
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