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International C291 Engine

The International Harvester C291 is a heavy-duty, inline 6-cylinder internal combustion engine designed primarily for agricultural and industrial applications. It belongs to a vintage family of International Harvester (IH) engines that shares structural design traits with the C221, C263, and C301 power units. The C291 block is engineered with heavy, flangeless press-fit cylinder sleeves. Operators commonly utilize this robust platform in mid-to-large-scale farm equipment, such as the Farmall 766 tractor. It is highly regarded by technicians for its durability and straightforward, serviceable layout.

The engine uses an overhead valve (OHV) design featuring two valves per cylinder, resulting in a total of 12 valves for the assembly. The timing gear train operates a side-mounted camshaft inside the engine block. This camshaft moves mechanical lifters, pushrods, and rocker arms to actuate the intake and exhaust valves. Technicians adjust the valve clearance at the rocker assembly during regular service intervals using standard manual adjustment screws. The engine features a total displacement of 291 cu.in (4.8 liters). The cylinder design consists of a 3.75" bore and a 4.39" stroke (95 mm by 112 mm).

The C291 engine is configured to run on either gasoline or liquefied petroleum gas (LPG). For gasoline models, a mechanical fuel pump draws fuel from the storage tank and delivers it directly to an up-draft or side-draft carburetor. LPG-configured models substitute the mechanical pump and traditional gasoline carburetor for a dedicated fuel regulator and specialized gas carburetor. The entire induction system pulls outside air through a heavy-duty, dual-stage dry air cleaner to protect internal components from field dust and debris. A mechanical governor connects directly to the throttle linkage to automatically stabilize engine speed under varying operational loads.

Lubrication is a full-pressure feed system managed by an internal, gear-driven oil pump. The oil pump draws lubricants from the bottom oil pan and forces oil through a full-flow oil filter channel. From there, it moves into drilled galleries to supply the main bearings, connecting rod bearings, camshaft bearings, and front timing gears. An external line or internal passage channels oil directly up to the rocker arm shaft to lubricate the top-end valve train. International Harvester recommends utilizing low-ash engine oil to specifically prevent dangerous carbon deposits from building up on the valves.

The engine uses a forced liquid-cooled system. A belt-driven centrifugal water pump mounts to the front cover of the engine block to circulate coolant through the engine jacket and cylinder head. A bypass thermostat controls the flow direction based on operating temperature. This setup routes coolant to the radiator for heat dissipation before drawing it back into the engine block.

General Technical Data

Engine Specifications

Engine Model ............... International Harvester C291
Engine Type ............... 4-cycle inline 6-cylinder overhead valve liquid-cooled gasoline
Number of Cylinders ............... 6
Cylinder Arrangement ............... In-line vertical
Engine Bore, in (mm) ............... 3.750 (95.250)
Engine Stroke, in (mm) ............... 4.390 (111.506)
Displacement, cu.in (L) ............... 291.2 (4.772)
Rated Engine Power, hp (kW) ............... 65-85 (48.5-63.4)
Rated Engine Speed, rpm ............... 2400
Peak Torque, lb-ft (Nm) ............... 210-235 (285-318) at 1200-1500 rpm
High Idle Speed, rpm ............... 2620-2650
Low Idle Speed, rpm ............... 700-750
Compression Ratio Gas Engine ............... 7.5:1-7.7:1
Compression Ratio LP Gas Engine ............... 8.8:1-9.0:1
Firing Order ............... 1-5-3-6-2-4
Cylinder Block Type ............... One-piece cast iron
Cylinder Head Type ............... Single piece cast iron
Lubrication System ............... Full-pressure recirculation
Oil Pump Type ............... Positive-displacement gear-driven internal oil pump
Oil Filter Type ............... Full-flow spin-on cartridge oil filtration system
Cooling System ............... Forced liquid circulation
Water Pump Type ............... V-belt driven centrifugal impeller design
Air Cleaner Type ............... Heavy duty dry dual-stage element
Spark Plug Type, Gas Variant ............... Champion D16 or equivalent
Spark Plug Gap, in (mm) ............... 0.023-0.027 (0.584-0.686)
Breaker Point Gap, in (mm) ............... 0.020 (0.508)
Starting System ............... Electric starter motor actuation
Ground Polarity ............... Negative ground system
Electrical System, V ............... 12

Fuel System

Fuel Type System ............... Gasoline or Liquefied Petroleum Gas (LPG)
Carburetor Manufacturer ............... Zenith or Marvel-Schebler
Carburetor Type ............... Mechanical updraft type
Carburetor Model (Gas) ............... Zenith 267 or Marvel-Schebler USX series
Carburetor Venturi Size, in (mm) ............... 1.181-1.299 (30.000-33.000)
Main Jet Type, Gasoline Variant ............... Fixed or adjustable metering needle
Idle Jet Type, Gasoline Variant ............... Calibrated air-bleed low speed fuel orifice circuit
Fuel Delivery Method ............... Mechanical diaphragm-type fuel pump or gravity feed
Fuel Pump Operating Pressure, psi (bar) ............... 3.5-5.0 (0.24-0.34)
LPG Regulator Manufacturer ............... Ensign or Impco multi-stage converter assembly
LPG Liquid Filter ............... Integrated porous ceramic or sintered bronze filter screen element
LPG Vaporizer Type ............... Engine coolant heated dual stage pressure reduction valve assembly
Choke Operation ............... Manual cable-controlled internal butterfly valve configuration
Float Setting Level, in (mm) ............... 1.281-1.344 (32.537-34.137)
Air-Fuel Operating Ratio ............... Stoichiometric to rich power mixture lean cruise range limits
Governor Type ............... Mechanical flyweight, integrated with timing gear drive train
Governor Control Linkage ............... Adjustable mechanical rod assembly

Dimensions and Weight

Overall Engine Length, in (mm) ............... 41.2 (1045)
Overall Engine Width, in (mm) ............... 22.4 (570)
Overall Engine Height, in (mm) ............... 36.6 (930)
Dry Engine Weight, lbs (kg) ............... 745-790 (338-358)
Wet Engine Weight, lbs (kg) ............... 795-845 (360-383)

Maintenance Data

Service Information

Compression Pressure, Minimum, psi (bar) ............... 125.0-145.0 (8.61-10.00)
Maximum Cylinder Pressure Variance, psi (bar) ............... 10.0-15.0 (0.68-1.03)
Engine Oil Pressure at Rated Speed, psi (bar) ............... 35.0-55.0 (2.41-3.79)
Engine Oil Pressure at Idle Speed, psi (bar) ............... 15.0-20.0 (1.03-1.37)
Thermostat Opening Temperature Base, F (C) ............... 165.0-175.0 (73.8-79.4)
Thermostat Full Open Temperature Limit, F (C) ............... 195.0-202.0 (90.5-94.4)
Cooling System Pressure Cap Valve Rating, psi (bar) ............... 7.0-9.0 (0.48-0.62)
Fan Belt Deflection Tension Indicator, in (mm) ............... 0.500-0.750 (12.700-19.050)
Dwell Angle Value Range, deg ............... 31.0-34.0
Initial Ignition Timing Dynamic, deg BTDC ............... 4.0-6.0
Total Centrifugal Advance Limit, deg ............... 22.0-25.0
Intake Valve Clearance, Cold, in (mm) ............... 0.027 (0.686)
Exhaust Valve Clearance, Cold, in (mm) ............... 0.027 (0.686)

Engine Oil and Coolant

Engine Oil Type .................. SAE 30, SAE 10W-30, or 15W-40
API Service Classifications ......................... CC or CD
Engine Oil Capacity with Filter, qt (L) ............... 8.0-9.0 (7.57-8.52)
Engine Oil Capacity Base Pan, qt (L) ............... 7.0-8.0 (6.62-7.57)
Cooling System Fluid Capacity, qt (L) ............... 22.0-26.0 (20.81-24.60)

Service Intervals

Change oil and filter ............... Every 150 hours
Inspect air cleaner ............... Every 50 hours
Service air cleaner ............... Every 500 hours
Valve clearance adjustment ............... Every 500 hours
Fuel system inspection ............... Every 1000 hours
Change coolant ............... Every 1000 hours
Spark plug replacement ............... Every 500 hours
Check ignition system ............... Every 500 hours

Service Specifications

Cylinder Liner Inside Diameter, in (mm) ............... 3.7500-3.7515 (95.250-95.288)
Cylinder Liner Out of Round Outflow Limit, in (mm) ............... 0.001 (0.025)
Crankshaft End Play, in (mm) ............... 0.004-0.008 (0.101-0.203)
Crankshaft Main Journal Outside Diameter, in (mm) ............... 2.748-2.749 (69.799-69.824)
Crankshaft Main Bearing Oil Clearance, in (mm) ............... 0.0020-0.0038 (0.050-0.096)
Crankpin Journal Outside Diameter, in (mm) ............... 2.374-2.375 (60.299-60.325)
Connecting Rod Bearing Oil Clearance, in (mm) ............... 0.0018-0.0033 (0.045-0.083)
Connecting Rod Center-to-Center Axial Length, in (mm) ............... 7.373-7.375 (187.274-187.325)
Connecting Rod Side Play Crankpin Journal, in (mm) ............... 0.007-0.013 (0.177-0.330)
Connecting Rod Bore Big End ID Without Bearing, in (mm) ............... 2.5245-2.5250 (64.122-64.135)
Piston Skirt Outside Diameter, in (mm) ............... 3.7465-3.7480 (95.161-95.199)
Piston to Cylinder Liner Clearance, in (mm) ............... 0.0030-0.0040 (0.076-0.101)
Piston Pin Bore Inner Diameter, in (mm) ............... 1.1252-1.1255 (28.580-28.587)
Piston Pin Outside Diameter, in (mm) ............... 1.1250-1.1252 (28.575-28.580)
Piston Pin Fit in Piston Boss, in (mm) ............... 0.0001-0.0004 (0.002-0.010)
Piston Pin Fit in Rod Bushing, in (mm) ............... 0.0004-0.0008 (0.010-0.020)
Top Ring Groove Width, in (mm) ............... 0.0950-0.0960 (2.413-2.438)
Second Ring Groove Width, in (mm) ............... 0.0950-0.0960 (2.413-2.438)
Oil Ring Groove Width, in (mm) ............... 0.1885-0.1895 (4.787-4.813)
Top Ring Side Clearance, in (mm) ............... 0.0020-0.0040 (0.050-0.101)
Second Ring Side Clearance, in (mm) ............... 0.0020-0.0035 (0.050-0.088)
Oil Ring Side Clearance, in (mm) ............... 0.0015-0.0035 (0.038-0.088)
Top Ring End Gap, in (mm) ............... 0.010-0.020 (0.254-0.508)
Second Ring End Gap, in (mm) ............... 0.010-0.020 (0.254-0.508)
Oil Ring End Gap, in (mm) ............... 0.010-0.020 (0.254-0.508)
Cylinder Head Flatness Warp Maximum Limit, in (mm) ............... 0.003 (0.076)
Cylinder Block Deck Face Flatness Warp Limit, in (mm) ............... 0.004 (0.101)
Intake Valve Stem Outside Diameter, in (mm) ............... 0.3715-0.3725 (9.436-9.461)
Exhaust Valve Stem Outside Diameter, in (mm) ............... 0.3705-0.3715 (9.410-9.436)
Valve Guide Inside Diameter, in (mm) ............... 0.3740-0.3750 (9.500-9.525)
Intake Valve Stem to Guide Clearance, in (mm) ............... 0.0015-0.0035 (0.038-0.088)
Exhaust Valve Stem to Guide Clearance, in (mm) ............... 0.0025-0.0045 (0.063-0.114)
Valve Guide Installation Extension Above Boss, in (mm) ............... 0.937 (23.800)
Valve Face Angle, deg ............... 45
Valve Seat Angle, deg ............... 45
Intake Valve Seat Width, in (mm) ............... 0.062-0.093 (1.574-2.362)
Exhaust Valve Seat Width, in (mm) ............... 0.062-0.093 (1.574-2.362)
Valve Spring Free Length, in (mm) ............... 2.185 (55.499)
Camshaft Journal Diameter (Number 1), in (mm) ............... 2.123-2.124 (53.924-53.949)
Camshaft Journal Diameter (Number 2), in (mm) ............... 2.060-2.061 (52.324-52.349)
Camshaft Journal Diameter (Number 3), in (mm) ............... 1.998-1.999 (50.749-50.774)
Camshaft Journal Diameter (Number 4), in (mm) ............... 1.935-1.936 (49.149-49.174)
Camshaft End Play, in (mm) ............... 0.003-0.007 (0.076-0.177)
Camshaft Journal Bearing Oil Clearance, in (mm) ............... 0.0015-0.0035 (0.038-0.088)
Intake Cam Lobe Lift, in (mm) ............... 0.275 (6.985)
Exhaust Cam Lobe Lift, in (mm) ............... 0.275 (6.985)
Rocker Arm Shaft Outside Diameter, in (mm) ............... 0.748-0.749 (18.999-19.024)
Rocker Arm Bushing Inside Diameter, in (mm) ............... 0.750-0.751 (19.050-19.075)
Rocker Arm to Shaft Oil Clearance, in (mm) ............... 0.001-0.003 (0.025-0.076)
Tappet Valve Lifter Body Outside Diameter, in (mm) ............... 0.998-0.999 (25.349-25.374)
Tappet Guide Bore Inside Block Diameter, in (mm) ............... 1.000-1.0015 (25.400-25.438)
Tappet to Block Guide Bore Clearance, in (mm) ............... 0.001-0.0035 (0.025-0.088)

Tightening Torques

Cylinder Head Bolts (Step 1), lb-ft (Nm) ............... 45.0 (61.0)
Cylinder Head Bolts (Step 2), lb-ft (Nm) ............... 85.0 (115.2)
Cylinder Head Bolts (Final Step), lb-ft (Nm) ............... 115.0 (155.9)
Main Bearing Cap Bolts ............... 90 lb-ft (122 Nm)
Connecting Rod Cap Nuts ............... 45 lb-ft (61 Nm)
Flywheel Bolts ............... 65 lb-ft (88 Nm)
Crankshaft Pulley Bolt ............... 150 lb-ft (203 Nm)
Camshaft Thrust Plate Bolts ............... 20 lb-ft (27 Nm)
Rocker Shaft Bracket Bolts ............... 30 lb-ft (41 Nm)
Intake Manifold Nuts ............... 25 lb-ft (34 Nm)
Exhaust Manifold Nuts ............... 25 lb-ft (34 Nm)
Water Pump Mounting Bolts ............... 25 lb-ft (34 Nm)
Oil Pan Bolts ............... 12 lb-ft (16 Nm)
Spark Plugs ............... 25 lb-ft (34 Nm)
Timing Cover Bolts ............... 12 lb-ft (16 Nm)
Starter Mounting Bolts ............... 45 lb-ft (61 Nm)

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• International Engines Specs
  
• International C175 Specs
  
• International C221 Specs
  
• International C263 Specs
  
• International C301 Specs
  

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