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Caterpillar 3066 Engine

The Caterpillar 3066 is a heavy-duty, inline 6-cylinder, four-stroke diesel engine engineered primarily for construction and industrial applications, most notably powering mid-sized hydraulic excavators like the CAT 320C. Developed in collaboration with Mitsubishi (often referenced under the S6K platform), this liquid-cooled, turbocharged engine is widely recognized for its mechanical simplicity, robust load-handling capabilities, and structural reliability under continuous heavy strain.

The fuel delivery setup features a highly robust, mechanical direct-injection system. Fuel is drawn from the supply tank by a mechanical transfer pump, routing through a primary fuel filter base and priming pump assembly to purge air. It is then fed into a multi-plunger, inline fuel injection pump timed directly to the engine front gear group. The injection pump pressurizes the fuel and sends it via rigid high-pressure fuel lines to individual multi-hole fuel injection nozzles seated in the cylinder head. Excess fuel from the injectors and the pump housing is returned safely to the fuel tank via a low-pressure fuel return line.

The engine utilizes a full-pressure lubrication circuit powered by a gear-driven oil pump mounted to the front gear train. Oil is drawn through a suction screen from the deep-sump oil pan and forced through a full-flow spin-on filter element. High-pressure oil channels through an integrated engine oil cooler directly into the main gallery to lubricate the crankshaft main bearings, connecting rod journals, and camshaft lobes. Oil holes aligned in the rocker arm bushings ensure targeted lubrication to the top-end valve train components.

Engine thermal regulation is managed via a closed-loop, forced-circulation water cooling system. A centrifugal water pump driven by the accessory belt circulates coolant through the internal engine block jackets and the cylinder head passages to absorb thermal energy. A wax-pellet type thermostat monitors coolant temperature at the water outlet housing, routing fluid through the bypass line during warmup, or directing it straight to the radiator once operational temperature thresholds are met.

General Technical Data

Engine Specifications

Engine Model ............... Caterpillar 3066
Engine Type ............... 4-cycle inline 6-cylinder direct injection turbocharged liquid-cooled diesel
Number of Cylinders ............... 6
Cylinder Arrangement ............... In-line
Engine Bore, in (mm) ............... 4.02 (102.0)
Engine Stroke, in (mm) ............... 5.12 (130.0)
Displacement, cu.in (L) ............... 400 (6.59)
Rated Engine Power, hp (kW) ............... 143 (107)
Rated Speed ............... 1800-2100 rpm
Idle Speed ............... 800-1000 rpm
Maximum Torque, Nm (lb-ft) ............... 540-590 (400-435) at 1600 rpm
Aspiration Type ............... Turbocharged
Operating Speed ............... 2100 rpm
Compression Ratio ............... 16.5:1
Firing Order ............... 1-5-3-6-2-4
Crankshaft Type ............... Forged steel
Piston Type ............... Cast-aluminum alloy
Con Rod Type ............... Forged steel
Cylinder Block Type ............... Cast iron
Cylinder Head Type ............... Cast iron
Lubrication System ............... Full-pressure
Oil Pump Type ............... Gear-driven
Oil Filter Type ............... Full-flow, spin-on
Cooling System ............... Liquid-cooled
Water Pump Type ............... Gear-driven, centrifugal
Air Cleaner Type ............... Dry two-stage
Starting System ............... Electric Starter
Electrical System ............... 24V
Alternator Rating, Amps ............... 45-65

Fuel System

Fuel System ............... Direct injection
Injection Pump Type ............... Mechanical
Fuel Injector Type ............... Multi-hole pencil-type
Governor Type ............... Mechanical
Fuel Type ............... Diesel Fuel

Dimensions and Weight

Overall Length, in (mm) ............... 52 (1320)
Overall Width, in (mm) ............... 31 (780)
Overall Height, in (mm) ............... 45 (1150)
Dry Weight, lbs (kg) ............... 1320 (600)

Maintenance Data

Service Information

Thermostat begins opening ............... 77C (170F)
Thermostat fully open ............... 90C (193F)
Cooling system pressure ............... 70-90 kPa (10-13 psi)
Operating oil pressure ............... 310-448 kPa (45-65 psi)
Intake Valve Clearance, in (mm) ............... 0.010 (0.25)
Exhaust Valve Clearance, in (mm) ............... 0.010 (0.25)

Engine Oil and Coolant

Engine Oil Type .................. SAE 10W-30, 15W-40
API Service Classifications ......................... CF-4, CG-4, CH-4, or CI-4
Engine Oil Capacity, qts (L) .................. 22.6 (21.5)
Coolant Capacity, qts (L) ............... 31.5 (30.0)

Service Intervals

Change oil and filter ............... Every 250 hours
Replace fuel filters ............... Every 500 hours
Inspect air filter ............... Every 50 hours
Change coolant ............... Every 2 years
Valve-lash adjustment ............... Every 1000 hours
Injector inspection ............... Every 1000-1500 hours
Compression test ............... Every 2000 hours
Belt inspection ............... As required

Service Specifications

Cylinder Bore Inside Diameter ................ 4.0157 in (102.000 mm)
Crankshaft Journal Outside Diameter ................ 3.5433 in (90.000 mm)
Crank Pin Outside Diameter ................ 2.3622 in (60.000 mm)
Crankshaft End Play ................ 0.0039-0.0098 in (0.100-0.250 mm)
Intake Valve Stem Outside Diameter ................ 0.3134 in (7.960 mm)
Exhaust Valve Stem Outside Diameter ................ 0.3126 in (7.940 mm)
Intake Valve Guide Inside Diameter (Installed) ................ 0.3150 in (8.000 mm)
Exhaust Valve Guide Inside Diameter (Installed) ................ 0.3150 in (8.000 mm)
Intake Valve Stem to Guide Clearance ................ 0.0012-0.0024 in (0.030-0.060 mm)
Exhaust Valve Stem to Guide Clearance ................ 0.0020-0.0033 in (0.050-0.085 mm)
Intake Valve Spring Free Length ................ 1.8898 in (48.000 mm)
Exhaust Valve Spring Free Length ................ 1.8898 in (48.000 mm)
Intake Cam Height ................ 1.8327 in (46.550 mm)
Exhaust Cam Height ................ 1.8327 in (46.550 mm)
Piston Pin Outside Diameter ................ 1.3386 in (34.000 mm)
Piston Pin to Piston Bore Clearance ................ 0.0003-0.0008 in (0.007-0.021 mm)
Top Ring Side Clearance ................ 0.0024-0.0039 in (0.060-0.100 mm)
Second Ring Side Clearance ................ 0.0020-0.0035 in (0.050-0.090 mm)
Oil Ring Side Clearance ................ 0.0012-0.0028 in (0.030-0.070 mm)
Top Ring End Gap ................ 0.0118-0.0177 in (0.300-0.450 mm)
Second Ring End Gap ................ 0.0118-0.0197 in (0.300-0.500 mm)
Oil Ring End Gap ................ 0.0098-0.0177 in (0.250-0.450 mm)

Tightening Torque Specs

Cylinder head bolts ............... 118 ± 5 Nm (87 ± 4 lb-ft)
Main bearing caps ............... 137 ± 5 Nm (100 ± 4 lb-ft)
Connecting rod bolts ............... 103 ± 5 Nm (75 ± 4 lb-ft)
Flywheel bolts ............... 185 Nm (137 lb-ft)
Crankshaft pulley bolt ............... 490 ± 10 Nm (360 ± 7 lb-ft)
Rocker Shaft Bolts ............... 10-20 Nm (7-15 lb-ft)
Exhaust Manifold Nuts ............... 18 ± 4 Nm (13 ± 3 lb-ft)

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