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Yanmar 2TN66L Engine

The Yanmar 2TN66L is a heavy-duty, vertical, in-line, two-cylinder, four-cycle diesel engine. Developed under Yanmar’s TN series, this liquid-cooled, naturally aspirated unit is primarily deployed in demanding industrial, military (Defense Agency), and power-generation configurations requiring a compact footprint and reliable thermal efficiency. The engine utilizes an overhead valve configuration driven by a gear-train camshaft layout, coupled with a specialized swirl combustion chamber design to achieve optimal fuel-air atomization, clean combustion, and minimal low-idle vibration.

Valve Operation: Overhead valve (OHV) setup featuring 1 intake valve and 1 exhaust valve per cylinder, operated via pushrods and rocker arms actuated by a gear-driven camshaft. Combustion System: Indirect injection with a specialized swirl-type combustion chamber designed to induce high vortex air flow during the compression stroke. Bore: 2.6 inches (approx. 66 mm). Stroke: 2.5 inches (approx. 64.2 mm). Total Displacement: 26.8 cubic inches (0.439 liters). Lubrication System: Forced oil lubrication pressurized via a high-efficiency trochoid pump. Oil Pressure Regulation: Integrated oil pressure switch calibrated to trigger at a minimum system pressure threshold of 7.3 psi. Cooling System: Forced liquid cooling managed via an engine-driven water pump, external radiator core, and thermostatically regulated bypass line.

Fuel Injection System: High-pressure direct/indirect configuration supplying fuel via rigid steel fuel lines to vertically mounted multi-hole injector nozzles. Injection Pump: Integrated inline fuel injection pump timed at 14 to 18 degrees BTDC depending on specific model suffix sub-variants. Governor Assembly: Varies by sub-specification; utilizes either a mechanical centrifugal all-speed governor or a simple electronic variable engine-type governor to manage fuel rack positioning relative to rotational speeds and load variation. Fuel Treatment: Primary filtration circuit incorporates an inline fuel filter paired with an integrated water separator block to protect the high-pressure components from moisture contamination.

General Technical Data

Engine Specifications

Engine Model ............... Yanmar 2TN66L
Engine Type ............... 4-cycle vertical inline 2-cylinder liquid-cooled diesel
Number of Cylinders ............... 2
Cylinder Arrangement ............... In-line vertical
Cylinder Bore, in (mm) ............... 2.60 (66.0)
Piston Stroke, in (mm) ............... 2.52 (64.0)
Total Displacement, cu.in (L) ............... 26.8 (0.439)
Compression Ratio ............... 21.0:1-23.0:1
Rated Engine Power, hp (kW) ............... 7.8 (5.8)
Rated Engine Speed, rpm ............... 2550
Maximum No-Load Speed, rpm ............... 2750
Minimum Idle Speed, rpm ............... 900-1000
Aspiration Type ............... Naturally aspirated
Firing Order ............... 1-2
Combustion Chamber ............... Swirl pre-combustion chamber type
Direction of Rotation ............... Counter-clockwise viewed from flywheel side
Exhaust Manifold Type ............... Horizontal rear or front discharge option
Suction Manifold Type ............... Cast aluminum alloy standard runner
Cylinder Block Material ............... High-strength cast iron
Cylinder Head Material ............... Cast iron alloy
Crankshaft Material ............... Forged steel alloy
Piston Material ............... High-silicon aluminum alloy
Lubrication System ............... Forced pressure circulation by trochoid pump
Oil Pump Type ............... Trochoid gear-driven pump
Oil Filter Type ............... Full-flow spin-on cartridge type
Cooling System ............... Liquid-cooled with centrifugal water pump
Water Pump Drive ............... V-belt driven from crankshaft pulley
Cooling Fan Type ............... Suction or pusher type plastic fan
Air Cleaner Type ............... Dry element with cyclone pre-cleaner
Starting System ............... Electric starting motor
Starting Motor Power ............... 12V-0.8kW
Electric System ............... 12V
Charging Output ............... 9A

Fuel System

Fuel Injection Pump Type ............... Yanmar YPES mini inline injection pump
Fuel Feed Pump Type ............... Mechanical diaphragm type or electric fuel pump
Fuel Injection Nozzle Type ............... Throttle type nozzle assembly
Fuel Injection Timing, deg ............... 14 BTDC
Fuel Injection Pressure, psi (MPa) ............... 1711-1856 (11.8-12.8)
Fuel Filter Type ............... Paper element cartridge with water separator
Fuel Feed Pressure, psi (kPa) ............... 2.9-4.3 (20.0-30.0)
Fuel Injection Pipe Inner Diameter, in (mm) ............... 0.059 (1.5)
Fuel Injection Pipe Outer Diameter, in (mm) ............... 0.236 (6.0)
Fuel Return Pipe Line Diameter, in (mm) ............... 0.157 (4.0)
Nozzle Valve Diameter, in (mm) ............... 0.157 (4.0)
Nozzle Valve Lift, in (mm) ............... 0.008 (0.2)
Governor Type ............... All-speed mechanical centrifugal weights
Fuel Tank Vent Pressure limit, psi (kPa) ............... 0.72 (5.0)
Fuel Temperature Maximum Limit, F (C) ............... 140 (60)
Plunger Diameter, in (mm) ............... 0.196 (5.0)
Plunger Stroke, in (mm) ............... 0.236 (6.0)
Delivery Valve Opening Pressure, psi (MPa) ............... 362 (2.5)
Nozzle Gasket Thickness, in (mm) ............... 0.039 (1.0)

Dimensions and Weight

Overall Length, in (mm) ............... 16.5 (420)
Overall Width, in (mm) ............... 15.3 (390)
Overall Height, in (mm) ............... 20.1 (510)
Dry Weight, lbs (kg) ............... 128 (58)

Maintenance Data

Service Information

Compression Pressure, Minimum, psi (MPa) ............... 426 (2.94)
Compression Pressure Between Cylinders, psi (MPa) ............... 28.4 (0.19)
Oil Pressure at Rated Speed, psi (kPa) ............... 28.4-56.8 (196.0-392.0)
Oil Pressure at Low Idle, psi (kPa) ............... 8.5 (58.8)
Oil Relief Valve Cracking Pressure, psi (MPa) ............... 56.8-71.1 (0.39-0.49)
Radiator Cap Pressure Rating, psi (kPa) ............... 12.8 (88.2)
Thermostat Valve Opening Temperature, F (C) ............... 158-165 (70.0-74.0)
Thermostat Valve Full Open Temperature, F (C) ............... 185 (85.0)
Coolant Temperature Warning Switch Activation, F (C) ............... 207-214 (97.0-101.0)
V-Belt Tension Deflection, in (mm) ............... 0.39-0.59 (10.0-15.0)
Intake Valve Clearance (Cold), in (mm) ............... 0.0079 (0.20)
Exhaust Valve Clearance (Cold), in (mm) ............... 0.0079 (0.20)

Engine Oil and Coolant

Engine Oil Type .................. SAE 30, SAE 10W-30, or SAE 10W
API Service Classifications ......................... CD, CE, CF, or CF-4
Engine Oil Capacity, Upper Level, gal (L) ............... 0.42 (1.6)
Engine Oil Capacity, Lower Level, gal (L) ............... 0.21 (0.8)
Coolant Capacity, Engine Only, gal (L) ............... 0.21 (0.8)
Coolant Capacity with Radiator, gal (L) ............... 0.66 (2.5)

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 300 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 Inner Diameter, in (mm) ............... 2.6000-2.6012 (66.000-66.030)
Cylinder Bore Out of Round, in (mm) ............... 0.0004 (0.010)
Cylinder Bore Taper Maximum, in (mm) ............... 0.0004 (0.010)
Main Bearing Journal Outer Diameter, in (mm) ............... 1.693 (43.0)
Crankshaft Main Journal Outer Diameter, in (mm) ............... 1.6913-1.6921 (42.960-42.980)
Main Bearing Clearance, in (mm) ............... 0.0015-0.0031 (0.038-0.080)
Crankpin Journal Outer Diameter, in (mm) ............... 1.4945-1.4953 (37.960-37.980)
Crankshaft Thrust Washer Thickness, in (mm) ............... 0.0768-0.0787 (1.950-2.000)
Crankshaft End Play, in (mm) ............... 0.0043-0.0090 (0.110-0.230)
Connecting Rod Center to Center Length, in (mm) ............... 4.133 (105.0)
Connecting Rod Bearing Clearance, in (mm) ............... 0.0015-0.0031 (0.038-0.080)
Connecting Rod Small End Bushing I.D, in (mm) ............... 0.7488-0.7496 (19.020-19.040)
Connecting Rod Big End Side Play, in (mm) ............... 0.0216 (0.550)
Piston Skirt Outer Diameter, in (mm) ............... 2.5968-2.5980 (65.920-65.950)
Piston to Cylinder Wall Clearance, in (mm) ............... 0.0020-0.0039 (0.050-0.100)
Piston Pin Bore Inner Diameter, in (mm) ............... 0.7480-0.7484 (19.000-19.010)
Piston Pin Outer Diameter, in (mm) ............... 0.7476-0.7480 (18.989-19.000)
Piston Pin to Piston Pin Bore Clearance, in (mm) ............... 0.0000-0.0008 (0.000-0.021)
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) ............... 0.1189-0.1197 (3.020-3.040)
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) ............... 0.0059-0.0118 (0.150-0.300)
Cylinder Head Lower Deck Surface Flatnes, in (mm) ............... 0.0019 (0.050)
Cylinder Block Upper Top Deck Surface Flatness, in (mm) ............... 0.0019 (0.050)
Intake Valve Stem Outer Diameter, in (mm) ............... 0.2343-0.2350 (5.950-5.970)
Exhaust Valve Stem Outer Diameter, in (mm) ............... 0.2339-0.2346 (5.940-5.960)
Valve Guide Inner Diameter, in (mm) ............... 0.2362-0.2368 (6.000-6.012)
Intake Valve Stem to Guide Clearance, in (mm) ............... 0.0011-0.0024 (0.030-0.062)
Exhaust Valve Stem to Guide Clearance, in (mm) ............... 0.0015-0.0028 (0.040-0.072)
Valve Sinkage Depth, in (mm) ............... 0.0157-0.0275 (0.400-0.700)
Valve Seat Angle, deg ............... 45
Valve Seat Face Width, in (mm) ............... 0.0433-0.0511 (1.100-1.300)
Valve Spring Free Length, in (mm) ............... 1.259 (32.0)
Camshaft Journal Outer Diameter (Front), in (mm) ............... 1.496 (38.0)
Camshaft Journal Outer Diameter (Middle), in (mm) ............... 1.456 (37.0)
Camshaft Journal Outer Diameter (Rear), in (mm) ............... 1.417 (36.0)
Camshaft Bearing Oil Clearance, in (mm) ............... 0.0020-0.0039 (0.050-0.100)
Intake Cam Lobe Height, in (mm) ............... 1.1791-1.1831 (29.950-30.050)
Exhaust Cam Lobe Height, in (mm) ............... 1.1791-1.1831 (29.950-30.050)
Tappet Guide Inner Diameter, in (mm) ............... 0.4724-0.4731 (12.000-12.018)
Tappet Body Outer Diameter, in (mm) ............... 0.4704-0.4712 (11.950-11.970)
Tappet to Block Guide Clearance, in (mm) ............... 0.0011-0.0026 (0.030-0.068)
Rocker Arm Shaft Outer Diameter, in (mm) ............... 0.4716-0.4724 (11.980-12.000)
Rocker Arm Bushing Inner Diamete, in (mm) ............... 0.4728-0.4740 (12.010-12.040)
Rocker Arm Shaft to Bushing Clearance, in (mm) ............... 0.0004-0.0023 (0.010-0.060)
Idler Gear Shaft Outer Diameter, in (mm) ............... 1.4547-1.4557 (36.950-36.975)
Idler Gear Bushing Inner Diameter, in (mm) ............... 1.4566-1.4582 (37.000-37.040)
Idler Gear Shaft to Bushing Clearance, in (mm) ............... 0.0009-0.0035 (0.025-0.090)

Tightening Torques

Cylinder Head Fastening Bolts, lb-ft (Nm) ............... 40-44 (54-60)
Connecting Rod Cap Bolts, lb-ft (Nm) ............... 17-20 (23-27)
Main Bearing Cap Bolts, lb-ft (Nm) ............... 40-44 (54-60)
Flywheel Mounting Center Bolts, lb-ft (Nm) ............... 58-65 (78-88)
Crankshaft Front Pulley Center Nut, lb-ft (Nm) ............... 61-72 (83-98)
Camshaft Thrust Plate Fasteners, lb-ft (Nm) ............... 7-9 (10-12)
Rocker Arm Shaft Support Bracket Bolts, lb-ft (Nm) ............... 17-23 (23-31)
Cylinder Head Valve Bonnet Cover Nuts, lb-ft (Nm) ............... 5-7 (7-10)
Flywheel Housing to Cylinder Block Bolts, lb-ft (Nm) ............... 17-23 (23-31)
Timing Gear Case Cover Front Attachment Bolts, lb-ft (Nm) ............... 7-9 (10-12)
Timing Gear Case Back Plate Base Bolts, lb-ft (Nm) ............... 17-23 (23-31)
Oil Pan Perimeter Sealing Sheet Metal Bolts, lb-ft (Nm) ............... 7-9 (10-12)
Oil Pan Drain Center Plug, lb-ft (Nm) ............... 36-43 (49-59)
Exhaust Manifold Flange Attachment Stud Nuts, lb-ft (Nm) ............... 17-23 (23-31)
Suction Air Intake Manifold Retaining Structural Bolts, lb-ft (Nm) ............... 7-9 (10-12)
Fuel Injection Pump Delivery Valve Spring Holders, lb-ft (Nm) ............... 26-30 (35-41)
Fuel Injection Pump Drive Gear Center Lock Nut, lb-ft (Nm) ............... 43-51 (59-69)
Fuel Injection Pump Mounting Flange Stud Nuts Torque, lb-ft (Nm) ............... 17-23 (23-31)
Fuel Injection Nozzle Holder Assembly Outer Shell, lb-ft (Nm) ............... 29-36 (39-49)
Fuel Injection Nozzle Retention Clamp Bracket Bolts, lb-ft (Nm) ............... 17-23 (23-31)
Fuel High-Pressure Injection Line Flare Union Nuts, lb-ft (Nm) ............... 22-25 (29-34)
Fuel Return Overflow Leak-Off Pipe Line Joint Bolt, lb-ft (Nm) ............... 6-8 (8-11)
Fuel Feed Pump Fuel Hose Eye Joint Union Bolt, lb-ft (Nm) ............... 6-8 (8-11)
Glow Plug Installation Thread Sleeves, lb-ft (Nm) ............... 11-15 (15-20)
Glow Plug Electrical Harness Terminal Small Nut, lb-ft (Nm) ............... 1.0-1.5 (1.4-2.0)
Oil Pressure Sensor Warning Switch, lb-ft (Nm) ............... 9-11 (12-15)
Coolant Temperature Indicator Gauge Sensor, lb-ft (Nm) ............... 22-29 (30-39)
Cooling Water Centrifugal Pump Mounting Bolts, lb-ft (Nm) ............... 17-23 (23-31)
Cooling System Fan Blade to Pulley Hub Attachment Bolts, lb-ft (Nm) ............... 7-9 (10-12)
Thermostat Housing Water Outlet Flange Cover Bolts, lb-ft (Nm) ............... 17-23 (23-31)
Electric Starter Motor Flange Mounting Bolts, lb-ft (Nm) ............... 33-40 (45-54)
Alternator Charging Unit Pivot Support Structural Swing Bolt, lb-ft (Nm) ............... 33-40 (45-54)
Alternator Belt Tensioner Adjustment Slotted Bracket Bolt, lb-ft (Nm) ............... 14-18 (19-24)
Oil Pump Trochoid Cover Recessed Screws, lb-ft (Nm) ............... 5-7 (7-10)
Oil Pressure Safety Regulating Relief Valve Plug, lb-ft (Nm) ............... 29-36 (39-49)
Crankcase Breather Assembly Shell Small Fasteners, lb-ft (Nm) ............... 5-7 (7-10)

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