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Caterpillar 3306C Engine

The Caterpillar 3306C is a highly refined, heavy-duty 10.5-liter (638 cubic inches) inline-six, four-stroke diesel engine. Serving as one of the final iterations of the legendary 3306 platform before electronic emissions engines took over, the "C" series brought critical structural updates. It features a redesigned, block-stiffening casting, a robust single-piece cylinder head, a total-hardened crankshaft, and a more responsive turbocharger system. Beloved by field mechanics for its lack of complex electronics, it utilizes a fully mechanical fuel injection setup that offers outstanding uptime and straightforward diagnostics in trucks, gensets, and heavy earthmoving machinery.

Fuel System Type: High-pressure mechanical direct injection. Injection Pump: Single, centrally mounted V-type mechanical injection pump assembly. It distributes fuel through individual steel lines to mechanical injectors located in each cylinder head. Timing and Regulation: Driven by a mechanical governor with an automatic timing advance unit to adjust injection timing relative to engine speed. Maintenance: The system requires comprehensive manual priming and bleeding via the hand priming pump if air enters the fuel lines.

Lubrication System Type: Full-pressure, wet-sump lubrication system. Components: Gear-driven oil pump, integral oil cooler bypass, and spin-on fluid filters. Service: Standard operation utilizes high-quality 15W-40 diesel-rated engine oil.

Cooling System Type: Liquid-cooled, closed-loop configuration. Components: Centrifugal water pump, dual water temperature regulators (thermostats), and a bypass circuit. Application Variants: Industrial models use standard radiators, while marine configurations integrate an engine-mounted heat exchanger alongside a raw-water auxiliary pump.

General Technical Data

Engine Specifications

Engine Model ............... Caterpillar 3306C
Engine Type ............... 4-cycle inline 6-cylinder direct injection liquid-cooled diesel
Number of Cylinders ............... 6
Cylinder Arrangement ............... In-line
Engine Bore, in (mm) ............... 4.76 (121.0)
Engine Stroke, in (mm) ............... 6.00 (152.0)
Displacement, cu.in (L) ............... 638 (10.5)
Rated Engine Power (Industrial), hp (kW) ............... 150-300 (112-224)
Rated Engine Power (Agricultural), hp (kW) ............... 140-260 (104-194)
Rated Engine Power (Marine), hp (kW) ............... 150-350 (112-260)
Rated Engine Speed, rpm ............... 1800-2000
Peak Torque ............... 750-1200 Nm (553-885 lb-ft) at 1200-1500 rpm
Idle Speed ............... 650-750 rpm
Aspiration Type ............... Naturally aspirated or Turbocharged
Operating Speed ............... 1900 rpm
Compression Ratio ............... 14.5:1-16.5:1
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 ............... Belt-driven, centrifugal
Air Cleaner Type ............... Dry dual-stage
Starting System ............... Electric Starter
Electrical System ............... 12V or 24V
Alternator Rating, Amps ............... 65-130

Fuel System

Fuel System ............... Direct injection
Injection Pump Type ............... Inline, plunger-type
Fuel System Control ............... Mechanical
Governor Type ............... Mechanical
Fuel Injector Type ............... Multi-hole
Fuel Type ............... Diesel Fuel

Dimensions and Weight

Overall Length, in (mm) ............... 55.2-65.1 (1400-1650)
Overall Width, in (mm) ............... 31.5-37.4 (800-950)
Overall Height, in (mm) ............... 41.3-49.2 (1100-1250)
Dry Weight, lbs (kg) ............... 2420-2860 (1100-1300)

Maintenance Data

Service Information

Thermostat begins opening ............... 82C (180F)
Thermostat fully open ............... 95C (203F)
Cooling system pressure ............... 70-100 kPa (10-15 psi)
Operating oil pressure ............... 300-450 kPa (44-65 psi)
Idle oil pressure ............... 100-150 kPa (15-22 psi)
Intake Valve Clearance, in (mm) ............... 0.015-0.017 (0.38-0.43)
Exhaust Valve Clearance, in (mm) ............... 0.025-0.027 (0.64-0.69)

Engine Oil and Coolant

Engine Oil Type .................. SAE 10W-30, 15W-40
API Service Classifications ......................... CD, CE, or CF-4
Engine Oil Capacity, qts (L) .................. 21.0-29.4 (20.0-28.0)
Coolant Capacity, qts (L) ............... 31.5-37.8 (30.0-36.0)

Service Intervals

Change oil and filter ............... Every 250 hours
Replace fuel filters ............... Every 300 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
Drain water separator ............... As required
Belt inspection ............... As required

Service Specifications

Cylinder Bore Inside Diameter, in (mm) ................ 4.750-4.752 (120.65-120.70)
Crankshaft Journal Outside Diameter, in (mm) ................ 3.4990-3.5000 (88.875-88.900)
Crank Pin Outside Diameter, in (mm) ................ 2.9987-3.0003 (76.167-76.208)
Crankshaft End Play, in (mm) ................ 0.007-0.025 (0.17-0.63)
Intake Valve Stem Outside Diameter, in (mm) ................ 0.3717-0.3725 (9.441-9.462)
Exhaust Valve Stem Outside Diameter, in (mm) ................ 0.3705-0.3713 (9.411-9.431)
Intake Valve Guide Inside Diameter (Installed), in (mm) ................ 0.3734-0.3744 (9.484-9.510)
Exhaust Valve Guide Inside Diameter (Installed), in (mm) ................ 0.3734-0.3744 (9.484-9.510)
Intake Valve Stem to Guide Clearance, in (mm) ................ 0.0009-0.0027 (0.022-0.069)
Exhaust Valve Stem to Guide Clearance, in (mm) ................ 0.0021-0.0039 (0.053-0.099)
Intake Valve Spring Free Length, in (mm) ................ 2.47 (62.7)
Exhaust Valve Spring Free Length, in (mm) ................ 2.47 (62.7)
Intake Cam Height, in (mm) ................ 1.844-1.856 (46.84-47.14)
Exhaust Cam Height, in (mm) ................ 1.844-1.856 (46.84-47.14)
Piston Pin Outside Diameter, in (mm) ................ 1.5011-1.5013 (38.128-38.133)
Piston Pin to Piston Bore Clearance, in (mm) ................ 0.0002-0.0008 (0.005-0.020)
Top Ring Side Clearance, in (mm) ................ 0.0031-0.0051 (0.079-0.130)
Second Ring Side Clearance, in (mm) ................ 0.0024-0.0043 (0.061-0.109)
Oil Ring Side Clearance, in (mm) ................ 0.0016-0.0035 (0.041-0.089)
Top Ring End Gap, in (mm) ................ 0.0170-0.0320 (0.432-0.813)
Second Ring End Gap, in (mm) ................ 0.0150-0.0270 (0.381-0.686)
Oil Ring End Gap, in (mm) ................ 0.0100-0.0220 (0.254-0.559)

Tightening Torque Specs

Cylinder head bolts ............... 270 Nm (200 lb-ft)
Main bearing cap bolts (Vertical) ............... 340 Nm (250 lb-ft)
Main bearing cap cross bolts ............... 160 Nm (118 lb-ft)
Connecting-rod bolts ............... 200 Nm (148 lb-ft)
Flywheel housing-to-block bolts ............... 160 Nm (118 lb-ft)
Flywheel-to-crankshaft bolts ............... 230 Nm (170 lb-ft)
Injector clamp bolt ............... 50 Nm (37 lb-ft)
Oil pan bolts ............... 55 Nm (41 lb-ft)
Oil filter cap or cartridge ............... 75 Nm (55 lb-ft)
Injector hold-downs ............... 35-45 Nm (26-33 lb-ft)

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