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International D166 Engine

The International Harvester D166 is a heavy-duty, inline 4-cylinder, naturally aspirated, liquid-cooled diesel engine introduced by International Harvester in 1960. Developed as a reliable power plant for mid-sized agricultural and industrial machinery, most notably powering the Farmall 340 tractor and the International TD-340 crawler, this engine is part of IH’s legendary family of glow-plug-assisted, indirect-injection diesels. Architecturally, it serves as the 4-cylinder sibling to the larger 6-cylinder D-236, D-282, and D-301 engines, sharing a high degree of parts commonality, design tolerances, and field service strategies.

The cylinder head utilizes an overhead valve (OHV) arrangement with 2 valves per cylinder (8 valves total), driven by a gear-driven camshaft via pushrods and rocker arms. Valve clearance adjustments must be performed mechanically at the rocker arm adjusting screws according to standard factory service clearance intervals. The engine features a total displacement of 166 cu.in (2.7 liters). The cylinder bore measures 3.68 inches (94 mm) and the piston stroke is 3.87 inches (98 mm). Internal architecture utilizes replaceable dry sleeve cylinder liners.

Fuel System: The D166 utilizes an indirect injection diesel design assisted by individual cylinder glow plugs threaded directly into pre-combustion chambers to facilitate reliable cold-weather starting. Mechanical fuel distribution is managed by a precisely timed Roosa Master distributor-type injection pump. This injection pump utilizes an integrated, internal automatic timing advance mechanism that responds dynamically to changes in internal fuel charging pressure. Fuel is supplied through multi-stage fuel filtration elements to high-pressure injectors calibrated to atomize the fuel directly into the pre-cup chambers.

Lubrication System: Lubrication is managed via a full-pressure, positive-displacement internal oil pump system delivering oil directly to the main bearings, connecting rods, camshaft, and rocker assemblies. Normal operating oil pressure registers at 50 psi when cold, dropping to a stable 40 psi under load at full operating temperature. Cooling System: Engine temperature regulation is achieved through a high-capacity, pressurized liquid-cooled system with a forced-centrifugal water pump and an operational bypass thermostat. The intake circuit includes an external oil-bath style air cleaner assembly to prevent debris ingestion in heavy agricultural environments.

General Technical Data

Engine Specifications

Engine Model ............... International Harvester D166
Engine Type ............... 4-cycle inline 4-cylinder overhead valve liquid-cooled diesel
Number of Cylinders ............... 4
Cylinder Arrangement ............... In-line
Engine Bore, in (mm) ............... 3.6875 (93.66)
Engine Stroke, in (mm) ............... 3.875 (98.425)
Displacement, cu.in (L) ............... 166 (2.72)
Rated Engine Power, hp (kW) ............... 47.0 (35.0)
Rated Engine Speed, rpm ............... 2400
Peak Torque ............... 112.0 lb-ft (151.8 Nm) at 1600 rpm
Idle Speed ............... 700-750 rpm
Aspiration Type ............... Naturally Aspirated
Operating Speed ............... 2400 rpm
Compression Ratio ............... 18.2:1
Firing Order ............... 1-3-4-2
Cylinder Block Type ............... Cast iron dry-sleeve liner structure
Cylinder Head Type ............... Cast iron overhead valve design
Camshaft Drive ............... Helical gear train system setup
Valves per Cylinder ............... 2 overhead valves per chamber unit
Combustion System ............... Pre-combustion chamber with glow plug inserts
Exhaust System ............... Heavy duty cast iron exhaust runner block
Lubrication System ............... Full-pressure gear pump supply
Oil Pump Type ............... Gear-driven internally mounted
Oil Filter Type ............... Full-flow spin-on cartridge setup
Cooling System ............... Liquid-cooled centrifugal circulation
Water Pump Type ............... Belt-driven centrifugal impeller layout
Air Cleaner Type ............... Oil-bath clean airflow assembly
Starting System ............... Electric starter assisted by glow plugs
Electrical System ............... 12V negative ground system

Fuel System

Injection Pump Model ............... Roosa Master DB distribution pump setup
Injection Pump Type ............... Rotary distributor mechanical drive pump
Injection Timing ............... 2.0 deg BTDC static position
Nozzle Assembly Type ............... Pintle multi-hole high pressure delivery orifice
Injection Opening Pressure, psi (bar) ............... 2000.0-2200.0 (137.9-151.7)
Fuel Transfer Pump Pressure, psi (bar) ............... 12.0-15.0 (0.83-1.03)
Primary Fuel Filter Type ............... Water separator sediment bowl mesh system
Secondary Fuel Filter Type ............... Replaceable spin-on fine media element
Glow Plug Voltage Rating ............... 12.0V parallel configuration circuit
Fuel Injection Lines Outer Diameter, in (mm) ............... 0.25 (6.35)
Governor Type ............... Mechanical flyweight variable speed
Fuel Leak-off System Layout ............... Overhead manifold returning straight to tank reservoir
High Idle Speed Limit, rpm ............... 2625-2650
Low Idle Speed Limit, rpm ............... 700-750

Dimensions and Weight

Engine Length, in (mm) ............... 31.4 (795)
Engine Width, in (mm) ............... 22.8 (580)
Engine Height, in (mm) ............... 34.6 (880)
Dry Weight, lbs (kg) ............... 585 (265)
Wet Weight, lbs (kg) ............... 635 (288)

Maintenance Data

Service Information

Compression Pressure, psi (bar) ............... 380.0-420.0 (26.2-28.9)
Maximum Pressure Between Cylinders, psi (bar) ............... 30.0 (2.06)
Fuel Pressure Injection Pump Inlet Line, psi (bar) ............... 8.0-12.0 (0.55-0.82)
Oil Filter Element Pressure Differential Bypass, psi (bar) ............... 15.0 (1.03)
Oil Pressure at Rated Speed, psi (bar) ............... 35.0-45.0 (2.41-3.1)
Oil Pressure at Idle Speed, psi (bar) ............... 15.0 (1.03)
Thermostat Opening Start Temperature, F (C) ............... 170.0 (76.6)
Thermostat Fully Open Temperature, F (C) ............... 190.0 (87.7)
Radiator Cap Pressure Rating, psi (bar) ............... 7.0 (0.48)
Fan Belt Tension Deflection Limit, in (mm) ............... 0.5 (12.7)
Intake Valve Lash, Cold, in (mm) ............... 0.014 (0.355)
Exhaust Valve Lash, Cold, in (mm) ............... 0.014 (0.355)

Engine Oil and Coolant

Engine Oil Type .................. SAE 10W, SAE 30W
API Service Classifications ......................... CC or CD
Engine Oil Capacity, qt (L) ............... 5.0-7.0 (4.7-6.6)
Coolant Capacity, qt (L) ............... 15.0-18.6 (14.2-17.6)

Service Intervals

Change oil and filter ............... Every 100 hours
Inspect air cleaner ............... Every 50 hours
Service air cleaner ............... Every 500 hours
Replace fuel filter ............... Every 250 hours
Valve clearance adjustment ............... Every 500 hours
Fuel system inspection ............... Every 1000 hours
Change coolant ............... Every 1000 hours
Compression test ............... Every 1000 hours
Belt inspection ............... Every service cycle

Service Specifications

Cylinder Bore Diameter, in (mm) ............... 3.6875-3.6890 (93.662-93.700)
Cylinder Bore Out-of-Round Maximum, in (mm) ............... 0.002 (0.051)
Cylinder Bore Taper Maximum, in (mm) ............... 0.003 (0.076)
Connecting Rod Small End Bushing ID, in (mm) ............... 1.1262-1.1268 (28.605-28.620)
Crankshaft Main Journal Diameter, in (mm) ............... 2.7485-2.7495 (69.812-69.837)
Main Journal Maximum Wear Out-of-Round, in (mm) ............... 0.001 (0.0254)
Main Bearing Shell to Journal Clearance, in (mm) ............... 0.0022-0.0038 (0.056-0.096)
Con Rod Journal Diameter, in (mm) ............... 2.2485-2.2495 (57.112-57.137)
Crankshaft End Play, in (mm) ............... 0.004-0.008 (0.102-0.203)
Piston to Cylinder Liner Clearance, in (mm) ............... 0.0045-0.0055 (0.114-0.140)
Piston Pin Bore Inside Diameter, in (mm) ............... 1.1252-1.1255 (28.580-28.587)
Piston Pin Outside Diameter, in (mm) ............... 1.1248-1.1250 (28.570-28.575)
Piston Pin to Piston Bushing Clearance, in (mm) ............... 0.0002-0.0007 (0.005-0.018)
Top Ring Groove Width, in (mm) ............... 0.0955-0.0965 (2.425-2.451)
Second Ring Groove Width, in (mm) ............... 0.0945-0.0955 (2.400-2.425)
Oil Ring Groove Width, in (mm) ............... 0.1885-0.1895 (4.788-4.813)
Top Ring End Gap, in (mm) ............... 0.012-0.022 (0.305-0.558)
Second Ring End Gap, in (mm) ............... 0.010-0.020 (0.254-0.508)
Oil Ring End Gap, in (mm) ............... 0.015-0.025 (0.381-0.635)
Cylinder Head Surface Flatness Limit, in (mm) ............... 0.004 (0.102)
Intake Valve Stem Outside Diameter, in (mm) ............... 0.3725-0.3735 (9.461-9.487)
Exhaust Valve Stem Outside Diameter, in (mm) ............... 0.3715-0.3725 (9.436-9.461)
Valve Guide Inside Diameter, in (mm) ............... 0.3745-0.3755 (9.512-9.537)
Valve Guide Outer Diameter, in (mm) ............... 0.5645-0.5655 (14.338-14.363)
Intake Valve Stem to Guide Clearance, in (mm) ............... 0.0010-0.0030 (0.025-0.076)
Exhaust Valve Stem to Guide Clearance, in (mm) ............... 0.0020-0.0040 (0.051-0.102)
Valve Face Angle, deg ............... 45
Valve Seat Angle, deg ............... 45
Valve Spring Free Length, in (mm) ............... 2.125 (53.97)
Camshaft Journal Diameter, in (mm) ............... 1.9980-1.9990 (50.749-50.774)
Camshaft Journal Oil Clearance, in (mm) ............... 0.0015-0.0035 (0.038-0.089)
Camshaft End Play, in (mm) ............... 0.003-0.007 (0.076-0.178)
Intake Cam Lobe Height, in (mm) ............... 0.3155 (8.013)
Exhaust Cam Lobe Height, in (mm) ............... 0.3125 (7.937)
Tappet Valve Lifter Body Outside Diameter, in (mm) ............... 0.9980-0.9985 (25.349-25.361)
Tappet Guide Bore Block Inside Diameter, in (mm) ............... 1.0000-1.0010 (25.400-25.425)
Tappet to Lifter Bore Oil Clearance, in (mm) ............... 0.0015-0.0030 (0.038-0.076)
Rocker Arm Shaft Oil Clearance, in (mm) ............... 0.0045 (0.114)
Rocker Arm Shaft Outer Diameter, in (mm) ............... 0.7485-0.7495 (19.012-19.037)
Rocker Arm Bushing Inside Diameter, in (mm) ............... 0.7505-0.7515 (19.062-19.088)
Crankshaft Gear to Idler Gear Backlash, in (mm) ............... 0.002-0.005 (0.051-0.127)
Camshaft Gear to Idler Gear Backlash, in (mm) ............... 0.002-0.005 (0.051-0.127)

Tightening Torques

Cylinder Head Boltrs (1-Step), lb-ft (Nm) ............... 45.0 (61.0)
Cylinder Head Bolts (2-Step), lb-ft (Nm) ............... 85.0 (115.2)
Cylinder Head Bolts (3-Step), lb-ft (Nm) ............... 115.0 (155.9)
Main Bearing Cap Bolts, lb-ft (Nm) ............... 110.0 (149.1)
Connecting Rod Cap Nuts, lb-ft (Nm) ............... 55.0 (74.6)
Flywheel Retaining Bolts, lb-ft (Nm) ............... 75.0 (101.7)
Flywheel Housing Perimeter Bolts, lb-ft (Nm) ............... 40.0 (54.2)
Camshaft Thrust Flange Plate Bolts, lb-ft (Nm) ............... 18.0 (24.4)
Camshaft Drive Gear Hub Center Bolt, lb-ft (Nm) ............... 65.0 (88.1)
Crankshaft Front Vibration Damper Screw, lb-ft (Nm) ............... 130.0 (176.2)
Timing Gear Case Cover Small Bolts, lb-ft (Nm) ............... 15.0 (20.3)
Timing Gear Idler Shaft Retainer Bolt, lb-ft (Nm) ............... 35.0 (47.4)
Rocker Arm Shaft Bracket Hold-down Nut, lb-ft (Nm) ............... 25.0 (33.9)
Valve Cover Retainer Small Stud Nuts, lb-ft (Nm) ............... 8.0 (10.8)
Engine Lubricating Oil Pan Drain Plug, lb-ft (Nm) ............... 35.0 (47.4)
Oil Pan Perimeter Flange Bolts, lb-ft (Nm) ............... 12.0 (16.2)
Oil Pump Internal Assembly Mount Screws, lb-ft (Nm) ............... 15.0 (20.3)
Fuel Injection Pump Drive Hub Gear Nut, lb-ft (Nm) ............... 45.0 (61.0)
Fuel Injection Pump Mounting Flange Nuts, lb-ft (Nm) ............... 25.0 (33.9)
High Pressure Fuel Injection Line Nuts, lb-ft (Nm) ............... 20.0 (27.1)
Fuel Injector Nozzle Retaining Clamp Bolts, lb-ft (Nm) ............... 15.0 (20.3)
Glow Plug Body Thread Hex Drive Base, lb-ft (Nm) ............... 12.0 (16.2)
Intake Manifold Runner Mounting Screws, lb-ft (Nm) ............... 22.0 (29.8)
Exhaust Manifold Runner Mounting Studs, lb-ft (Nm) ............... 30.0 (40.6)
Water Pump Casting Mount Housing Bolts, lb-ft (Nm) ............... 20.0 (27.1)
Water Pump Pulley Retaining Small Bolts, lb-ft (Nm) ............... 10.0 (13.5)
Thermostat Housing Cover Retaining Screws, lb-ft (Nm) ............... 15.0 (20.3)
Oil Cooler Core Body Adapter Studs, lb-ft (Nm) ............... 25.0 (33.9)
Oil Pressure Sensor Sending Unit Threads, lb-ft (Nm) ............... 12.0 (16.2)
Coolant Temperature Indicator Switch Body, lb-ft (Nm) ............... 15.0 (20.3)
Starter Motor Flange Secure Mounting Screws, lb-ft (Nm) ............... 45.0 (61.0)
Alternator Pivot Support Anchor Long Bolt, lb-ft (Nm) ............... 35.0 (47.4)
Alternator Adjusting Strap Tensioning Bolt, lb-ft (Nm) ............... 18.0 (24.4)
Fan Hub Assembly Bracket Mount Studs, lb-ft (Nm) ............... 28.0 (37.9)
Air Cleaner Ducting Bracket Screw Clamps, lb-ft (Nm) ............... 6.0 (8.1)
Fuel Filter Header Bracket Mount Screws, lb-ft (Nm) ............... 22.0 (29.8)

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