International C291 Specifications
| Engine Model: International Harvester C291 |
| Engine Type: 4-stroke in-line 6-cylinder liquid-cooled gasoline |
| Total Displacement: 291 cu.in (4.8 L) |
| Rated Engine Power: 85-95 Hp (63-71 kW) at 2400 rpm |
| Fuel System Type: Updraft carburetor |
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The International C291 is a heavy-duty, inline
6-cylinder gasoline engine produced by International Harvester (IH).
Introduced in the early 1960s, it represented the largest displacement
variant within a dedicated family of small-block six-cylinder engines
that International Harvester developed for agricultural and industrial
applications. The C291 was engineered as a naturally aspirated,
carbureted, overhead-valve (OHV) powerplant, prioritizing torque
delivery at low and medium engine speeds.
This design philosophy made the engine exceptionally suitable for
sustained heavy-load operation in demanding environments such as field
cultivation and power take-off (PTO)-driven implements. The engine
gained its strongest reputation as the standard gasoline power source
for early production runs of the International 706 and 806 tractors,
later also appearing in updated chassis like the 756.
A notable engineering feature is the seven-main-bearing crankshaft,
which provides superior crankshaft support and contributes to smooth
running characteristics uncommon for a large-displacement six-cylinder
engine of this era. The C291 also offered fuel flexibility through
dedicated LP Gas versions, which utilized higher compression ratios and
modified carburetion for alternative fuel operation.
The International C291 is a 4-stroke, inline 6-cylinder engine designed
for slow-speed, high-torque operation. The engine architecture follows a
conventional 90-degree crankshaft configuration with an evenly spaced
firing interval. The bore and stroke relationship is undersquare,
meaning stroke exceeds bore, promoting high torque at low revolutions
per minute. The engine is spark-ignited and operates on a carbureted
fuel system. The valve train is located in the cylinder block, with
pushrods and rocker arms actuating overhead valves. Cooling is forced
circulation using a belt-driven centrifugal water pump.
Engine Type: Inline 6-cylinder, 4-stroke, gasoline (LP Gas variant
available)
Displacement: 291 cu.in (4.8 L)
Bore x Stroke: 3.75 in x 4.39 in (95.25 mm x 111.5 mm)
Compression Ratio (Gasoline): 7.5:1
Compression Ratio (LP Gas): 8.0:1
Firing Order: 1-5-3-6-2-4
Ignition System: Battery ignition with distributor, breaker points, and
coil
Governed Speed Range: 600-2,400 rpm
Gross Horsepower: 85-95 hp @ 2,400 rpm (63-71 kW)
PTO Horsepower: 72-76 hp @ 2,400 rpm (54-57 kW)
Drawbar Horsepower: 63-67 hp @ 2,400 rpm (47-50 kW)
Peak Torque: 225-235 lb-ft @ 1,200-1,400 rpm (305-319 Nm)
The cylinder block is constructed from high-strength cast iron,
employing a deep-skirt design. A deep-skirt block extends the cylinder
walls below the crankshaft centerline, providing substantial rigidity
and reducing torsional flex under heavy loads. The most significant
feature of the C291 block is the incorporation of replaceable wet
cylinder liners. Unlike a parent-bore block where pistons run directly
against cast iron, the wet liner design allows individual cylindrical
sleeves to be removed and replaced during an overhaul without machining
the block itself.
Each liner contacts the engine coolant directly on its external surface,
which provides superior heat transfer away from the combustion zone. The
block contains seven main bearing bulkheads with reinforced ribs to
support the crankshaft. The crankcase incorporates a cast oil sump
mounting flange with a gasket sealing surface. Cast-in passages route
oil from the pump to the main bearings and up to the cylinder head
through the block deck. Freeze plugs are installed in the block sides to
protect against coolant expansion damage in cold conditions.
The cylinder head is a single-piece cast iron unit that covers all six
cylinders. It features a wedge-style combustion chamber design, where
the combustion chamber is formed primarily within the head, and the
piston crown is nearly flat. This configuration promotes swirl and
efficient flame propagation at low engine speeds. The overhead valve
arrangement employs inline valves arranged in a single row along the
head centerline, with intake and exhaust valves positioned parallel to
each other.
Valve actuation is performed by a mechanical valvetrain consisting of a
camshaft located in the cylinder block, hydraulic or solid lifters,
pushrods passing through passages in the cylinder head, and forged steel
rocker arms mounted on a rocker shaft. The intake and exhaust valves are
seated on pressed-in alloy steel valve seats. Valve guides are
replaceable units pressed into the head casting. The cylinder head
gasket is a composite metal and asbestos-free material designed to
accommodate the wet liner protrusion above the block deck. The head is
secured to the block using a series of high-strength studs or bolts
arranged around each cylinder.
Valves per Cylinder: 2 (1 intake, 1 exhaust)
Valve Arrangement: Overhead valve (OHV), inline
Valve Lash (Hot, Solid Lifters): Intake/Exhaust 0.027 in (0.69 mm)
Valve Seat Angle: 45 degrees
Valve Head Diameter (Intake/Exhaust): 1.72-1.50 in (43.7-38.1 mm)
Valve Stem Diameter (Intake/Exhaust): 0.342-0.342 in (8.69-8.69 mm)
The fuel system for the gasoline version of the C291 employs a
mechanical fuel pump mounted on the cylinder block, operated by an
eccentric lobe on the camshaft. The pump draws fuel from the fuel tank
and delivers it to an updraft carburetor. The updraft carburetor,
manufactured by Zenith or Marvel-Schebler depending on the application,
is positioned below the intake manifold. Air enters through an oil-bath
air cleaner, passes upward through the carburetor venturi where fuel is
drawn into the airstream by engine vacuum, and then travels into the
intake manifold.
The intake manifold is a single-plane cast iron unit with a central
plenum feeding six individual runners. The carburetor includes an idle
circuit, main metering circuit, power enrichment circuit, and a
mechanical or vacuum-operated governor linkage to maintain engine speed
under varying loads. The LP Gas variant replaces the carburetor with a
vaporizer-regulator and a mixer mounted on the intake manifold. Fuel
enters as a liquid from the LP tank, passes through a vaporizer using
engine coolant heat to convert it to vapor, and is then metered through
a gas valve before mixing with intake air.
Fuel Type: Regular gasoline (minimum 85 octane) or LP Gas
Carburetor Type: Single-barrel updraft, Zenith or Marvel-Schebler
Fuel Pump Type: Mechanical diaphragm, camshaft-driven
Air Cleaner: Oil-bath type with replaceable element
Fuel Tank Capacity (Tractor): 20-25 US gal (76-95 L)
Fuel Consumption (Full Load): 4.5-5.5 US gal per hour (17-21 L/h)
The lubrication system is a full-pressure, forced-feed design. A
gear-type oil pump, driven directly from the camshaft or distributor
shaft, draws oil from the oil pan through a submerged strainer. The pump
delivers oil under pressure to a full-flow oil filter, which can be
either a spin-on or a replaceable canister-style element depending on
the production year. After filtration, oil is routed through a main oil
gallery machined into the cylinder block. From this gallery, passages
direct oil to the seven main bearings. From each main bearing, oil is
fed through drilled passages in the crankshaft to the connecting rod
bearings.
The connecting rods feature small holes that spray oil onto the cylinder
walls and the underside of the pistons. Oil is also routed upward from
the main gallery through external or internal passages to the cylinder
head, feeding the rocker shaft. The rocker arms have precision-clearance
holes that allow oil to drip onto the valve stems and pushrod tips. An
oil pressure relief valve, located near the oil pump or filter base,
maintains system pressure between 35 and 45 psi when the engine is warm
and operating above idle. The oil pan is constructed from stamped steel
with a drain plug at its lowest point.
Oil Type: Heavy-duty diesel or gasoline engine oil (SAE 30 or 10W-30)
Total Oil Capacity (including filter): 9 US qt (8.5 L)
Oil Pressure (Operating, warm): 35-45 psi (241-310 kPa)
Oil Pressure (Idle, warm): 10 psi (69 kPa) minimum
Oil Filter Type: Full-flow, spin-on or canister
Oil Pump Type: Gear-type, positive displacement
The cooling system is a pressurized, thermosiphon-assisted forced
circulation design. A centrifugal water pump, mounted on the front of
the cylinder block and driven by a V-belt from the crankshaft pulley,
circulates coolant throughout the engine and radiator. Coolant enters
the bottom of the water pump, is discharged into the cylinder block, and
flows upward around the wet cylinder liners and into the cylinder head.
The coolant then travels forward through the cylinder head to the
thermostat housing. A wax-pellet thermostat regulates coolant flow to
the radiator. When closed, coolant bypasses the radiator and returns
directly to the water pump for rapid warm-up. When open, coolant is
directed to the top tank of the radiator, passes downward through the
core tubes, and re-enters the water pump.
The radiator is a vertical-flow, tube-and-fin construction with a
removable pressure cap. A belt-driven fan, mounted on the water pump
hub, draws air through the radiator core. A shroud directs airflow for
maximum efficiency at low engine speeds encountered during stationary
PTO operation. Coolant capacity varies with chassis configuration, with
larger radiators fitted to tractor applications compared to combine or
industrial power unit installations.
Coolant Type: Conventional green ethylene glycol antifreeze
Total Cooling System Capacity (Tractor): 24-28 US qt (22.7-26.5 L)
Thermostat Opening Temperature: 160-180 °F (71-82 °C)
Radiator Cap Pressure: 4-7 psi (28-48 kPa)
Water Pump Type: Centrifugal, sealed bearing
Fan Drive: V-belt, adjustable tension
| Intake and Exhaust Systems |
Intake System: Air enters through an oil-bath air cleaner mounted on the
intake manifold side of the engine. The oil-bath design draws air
downward through a central tube, forcing it to change direction
abruptly. Heavy dirt particles fall into a reservoir of oil, while finer
particles are trapped as air passes through a mesh element wetted with
oil. This system is highly effective in dusty agricultural environments
and requires periodic cleaning and oil replacement.
Exhaust System: The exhaust manifold is a single-piece cast iron unit
with six ports merging into a single outlet. The manifold is mounted on
the opposite side of the cylinder head from the intake manifold, a
crossflow arrangement that keeps the intake charge cool. The exhaust
outlet is positioned near the front of the engine for convenient
connection to a vertical tractor muffler or horizontal industrial
exhaust pipe.
Ignition System: The battery ignition system consists of a distributor
with a centrifugal advance mechanism, a breaker point assembly, a
condenser, an ignition coil, and spark plugs. The distributor is driven
by a gear on the camshaft. Centrifugal advance adjusts ignition timing
based on engine speed, with a fixed initial timing set by rotating the
distributor housing. A mechanical governor on the carburetor controls
throttle position, not ignition timing. The LP Gas version uses a
similar ignition system but may employ a higher-energy ignition coil and
different spark plug heat range due to the different combustion
characteristics of LP gas.
Governor System: A mechanical, flyball-type governor is integrated into
the timing gear cover. The governor responds to engine speed changes and
adjusts the carburetor throttle plate to maintain a constant speed under
varying loads. This is essential for PTO-driven implements that require
steady rotational speed regardless of load. The governor linkage
connects directly to the carburetor throttle shaft.
Starter and Charging System: The engine is started by a heavy-duty,
solenoid-operated electric starter motor mounted on the flywheel
housing. The charging system uses a belt-driven generator (or alternator
on later production units) to maintain the battery and supply power for
ignition and lights.
Overall Length (front of fan to rear of flywheel): 42 in (1,067 mm)
Overall Width (across exhaust and intake manifolds): 24 in (610 mm)
Overall Height (crankshaft centerline to top of air cleaner): 36 in (914
mm)
Crankshaft Centerline to Top of Cylinder Head: 16 in (406 mm)
Crankshaft Centerline to Bottom of Oil Pan: 11 in (279 mm)
Dry Weight (complete assembly, no fluids): 850-900 lbs (386-408 kg)
Wet Weight (with all fluids): 915-970 lbs (415-440 kg)
Engine Oil Change Interval: 100 operating hours (yearly if less).
Engine Oil Filter Change Interval: Replace with every oil change.
Oil Bath Air Cleaner Service Interval: Clean and re-oil every 50 hours.
Spark Plug Type: Champion J8, AC Delco 45, or equivalent.
Spark Plug Gap: 0.025 in (0.64 mm).
Spark Plug Replacement Interval: 200 operating hours.
Breaker Point Gap: 0.020 in (0.51 mm).
Condenser Replacement Interval: Replace with every point change.
Ignition Timing (Initial, static): 4-6 degrees before top dead center
(BTDC).
Valve Lash Adjustment Interval: Inspect and adjust every 250 hours.
Intake Valve Lash (Hot, Solid Lifters): 0.027 in (0.69 mm).
Exhaust Valve Lash (Hot, Solid Lifters): 0.027 in (0.69 mm).
Engine Coolant Replacement Interval: 500 hours or 2 years.
Drive Belt Inspection Interval: Inspect every 100 operating hours.
Governed Idle Speed (No Load): 600 rpm.
Governed High Speed (No Load): 2,400 rpm.
Crankshaft End Play (New): 0.004-0.008 in (0.10-0.20 mm).
Cylinder Head Nuts: 70 lb-ft (95 Nm)
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)
Oil Pan Bolts: 12 lb-ft (16 Nm)
Water Pump Mounting Bolts: 25 lb-ft (34 Nm)
Spark Plugs: 25 lb-ft (34 Nm)
Timing Cover Bolts: 12 lb-ft (16 Nm)
Starter Mounting Bolts: 45 lb-ft (61 Nm)
The International C291 found its primary market in agricultural
tractors, where its torque characteristics matched the requirements of
tillage and PTO-driven equipment. The engine was also offered in
industrial power units for stationary applications and in self-propelled
combines.
The LP Gas version was popular in regions where propane was less
expensive than gasoline or for enclosed applications where cleaner
exhaust was desirable. The C291 was superseded by the larger C301 and
C351 engines in later tractor models, but it remained a respected
powerplant for its balance of displacement, durability, and
serviceability.
1963-1967 International 706 (Gas/LP): Early production standard gasoline
engine.
1963-1967 International 806 (Gas/LP): Early production gasoline option
(later replaced by C301).
1967-1971 International 756 (Gas/LP): Updated chassis with the same base
engine.
International 151 Combine: Self-propelled combine application.
International 181 Combine: Self-propelled combine application.
International UC-291 Power Unit: Stationary industrial engine for pumps,
generators, and sawmills.
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