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Caterpillar 3304 Engine

The Caterpillar 3304 is a heavy-duty, inline four-cylinder, four-stroke cycle diesel engine engineered for industrial, marine, and earthmoving applications. Derived directly as a four-cylinder variant of the highly regarded 3306 platform, it features a rugged gray iron block, cylinder head, and induction-hardened wet-sleeve liners. The engine is widely recognized in field service for its mechanical simplicity, long-term structural reliability, and ease of rebuilding under standard workshop conditions.

The fuel system is a completely mechanical, direct-injection or pre-combustion system managed by a heavy-duty fuel injection pump assembly. Fuel Transfer and Filtering: A mechanical, piston-type fuel transfer pump draws fuel from the supply tank through primary and secondary fuel filter groups, delivering low-pressure fuel to the injection pump's internal fuel gallery at a steady operating pressure. High-Pressure Injection: A dedicated pump camshaft moves internal plungers within the injection pump housing. These plungers timely compress the fuel to extreme high pressures to atomize the fluid past the delivery valves and down through the high-pressure fuel lines into individual fuel injection nozzles or capsules.

The lubrication system is a full-pressure, force-fed system relying on a gear-driven oil pump located within the lower engine crankcase. The oil pump draws lubrication directly from the oil pan and routes it through an engine oil cooler core and a full-flow spin-on oil filter. System Protection: Separate, spring-loaded bypass valves are integrated into both the oil cooler and oil filter bases to ensure uninterrupted component lubrication during cold starts or in the event of filter restriction. Component Delivery: Internal block galleries distribute pressurized oil directly to the main bearings, connecting rod journals, camshaft bearings, and turbocharger supply lines. Internal piston cooling jets spray oil onto the underside of the pistons, while vertical oil passages direct lubrication up into the rocker arm shafts to lubricate the top-end valve train.

The engine employs a pressurized, jacket-water closed cooling loop managed by a gear-driven centrifugal water pump. Flow and Temperature Control: The water pump forces coolant through the internal passages of the engine block, around the wet cylinder liners, and up through the spacer plate and water seals into the cylinder head. Conventional heat regulation is maintained by a mechanical thermostat assembly that restricts flow to the radiator or heat exchanger until the engine reaches normal operating temperature, rerouting cold coolant through a bypass line back to the water pump inlet.

General Technical Data

Engine Specifications

Engine Model ............... Caterpillar 3304
Engine Type ............... 4-cycle inline 4-cylinder direct injection liquid-cooled diesel
Number of Cylinders ............... 4
Cylinder Arrangement ............... In-line
Engine Bore, in (mm) ............... 4.76 (121.0)
Engine Stroke, in (mm) ............... 6.00 (152.0)
Displacement, cu.in (L) ............... 425 (7.0)
Rated Engine Power (Industrial), hp (kW) ............... 70-140 (52-104)
Rated Engine Power (Construction), hp (kW) ............... 85-140 (63-104)
Rated Engine Power (Generator), hp (kW) ............... 54-162 (40-120)
Rated Engine Speed, rpm ............... 1500-2200
Peak Torque ............... 350-550 Nm (258-406 lb-ft) at 1300-1600 rpm
Idle Speed ............... 650-750 rpm
Aspiration Type ............... Naturally Aspirated or Turbocharged
Operating Speed ............... 2000 rpm
Compression Ratio ............... 16.0:1 or 15.0:1
Firing Order ............... 1-3-4-2
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 ............... 35-70

Fuel System

Fuel System ............... Direct injection
Injection Pump Type ............... Rotary
Fuel System Control ............... Mechanical
Governor Type ............... Mechanical
Fuel Injector Type ............... Multi-hole
Fuel Type ............... Diesel Fuel

Dimensions and Weight

Overall Length, in (mm) ............... 37-43 (950-1100)
Overall Width, in (mm) ............... 29-33 (750-850)
Overall Height, in (mm) ............... 37-45 (950-1150)
Dry Weight, lbs (kg) ............... 1650-1870 (750-850)

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 ......................... CI-4 or higher
Engine Oil Capacity, qts (L) .................. 20.0-23.1 (19.0-22.0)
Coolant Capacity, qts (L) ............... 14.7-21.0 (14.0-20.0)

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 ............... 250-300 Nm (184-221 lb-ft)
Main-bearing caps ............... 300-350 Nm (221-258 lb-ft)
Connecting-rod bolts ............... 110-130 Nm (81-96 lb-ft)
Flywheel bolts ............... 200-240 Nm (148-177 lb-ft)
Crankshaft pulley bolt ............... 350-450 Nm (258-332 lb-ft)
Oil drain plug ............... 40-55 Nm (30-41 lb-ft)
Injector hold-downs ............... 25-30 Nm (18-22 lb-ft)

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• Caterpillar Engines Specs
  
• Cat 3204 Specs
  
• Cat 3208 Specs
  
• Cat 3208T Specs
  
• Cat 3208TA Specs
  
• Cat 3304B Specs
  
• Cat 3306 DITA Specs
  

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