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Caterpillar 3126 DITA Engine

The Caterpillar 3126 DITA (Direct Injection, Turbocharged, Aftercooled) is a medium-duty, inline 6-cylinder, 4-stroke diesel engine designed for industrial, marine, marine propulsion, and generator set applications. It serves as a rugged, highly versatile powerhouse featuring a cast-iron parent-bore block, deep-skirt design, and a 3-valve cylinder head structure. It represents one of Caterpillar's primary steps into precision electronic mid-range management, engineered to maintain operational reliability under heavy load cycles.

Fuel system operation relies on Caterpillar's HEUI (Hydraulic Electronic Unit Injection) assembly. This system utilizes an engine-driven high-pressure hydraulic pump that draws engine oil to pressurize the fuel injectors independently of engine speed. A mechanical fuel transfer pump draws fuel from the storage tank through a spin-on primary filter/water separator and secondary filtration lines. The Electronic Control Module (ECM) regulates the HEUI actuation pressure and electrical signals to the unit injectors, monitoring real-time load parameters to precisely adjust injection timing and fuel quantity.

The lubrication configuration utilizes a gear-driven engine oil pump providing a pressurized flow throughout the system. Oil passes through an engine-mounted oil cooler and a full-flow filtration system with spin-on elements. Refill capacity is 25 liters (6.6 U.S. gallons) for deep-pan applications, and approximately 18 liters (4.75 U.S. gallons) for shallow truck pans. Standard operating oil pressure at full throttle ranges from 40 to 60 psi under normal thermal operating conditions.

This engine utilizes a water-cooled design containing an engine jacket system paired with an expansion tank. For marine and specialized industrial environments, it features a dual-pump setup: a belt-driven centrifugal jacket water pump alongside a gear-driven auxiliary sea water/raw water pump. High-efficiency heat exchangers handle the thermal loads from both the jacket water and the aftercooler circuit.

General Technical Data

Engine Specifications

Engine Model ............... Caterpillar 3126 DITA
Engine Type ............... 4-cycle inline 6-cylinder turbocharged ATAAC liquid-cooled diesel
Number of Cylinders ............... 6
Cylinder Arrangement ............... In-line
Engine Bore, in (mm) ............... 4.33 (110.0)
Engine Stroke, in (mm) ............... 5.00 (127.0)
Displacement, cu.in (L) ............... 439 (7.2)
Rated Engine Power (Medium Duty Truck), hp (kW) ............... 170-250 (127-186)
Rated Engine Power (Industrial), hp (kW) ............... 275-330 (205-246)
Rated Engine Power (Marine), hp (kW) ............... 300-420 (224-313)
Rated Engine Speed, rpm ............... 2400-2800
Peak Torque ............... 420-860 lb-ft (570-1170 Nm) at 1400-1600 rpm
Aspiration Type ............... Turbocharged and aftercooled
Operating Speed ............... 2200-2800 rpm
Compression Ratio ............... 17.0:1
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 ............... 12V or 24V
Alternator Rating, Amps ............... 105-150

Fuel System

Fuel System ............... High-Pressure Electronic Unit Injection (HEUI)
Fuel Pump Type ............... Gear-type, transfer
Governor Type ............... Electronic
Injection Pressure, bar ............... 800-1100
Fuel Type ............... Diesel Fuel

Dimensions and Weight

Overall Length, in (mm) ............... 42.8 (1085)
Overall Width, in (mm) ............... 26.5 (675)
Overall Height, in (mm) ............... 36.5 (925)
Dry Weight, lbs (kg) ............... 1320 (600)

Maintenance Data

Service Information

Thermostat begins opening ............... 82C (180F)
Thermostat fully open ............... 95C (203F)
Cooling system pressure ............... 70-90 kPa (10-13 psi)
Operating oil pressure ............... 275-550 kPa (40-80 psi)
Idle oil pressure ............... 100-140 kPa (15-20 psi)
Intake Valve Clearance, in (mm) ............... 0.015 (0.38)
Exhaust Valve Clearance, in (mm) ............... 0.025 (0.64)

Engine Oil and Coolant

Engine Oil Type .................. SAE 10W-30, 15W-40
API Service Classifications ......................... CH-4, CG-4, CI-4, or higher
Engine Oil Capacity, qts (L) .................. 21.0-26.2 (20.0-25.0)
Coolant Capacity, qts (L) ............... 40.0-50.0 (38.0-47.5)

Service Intervals

Change oil and filter ............... Every 250 hours
Replace fuel filters ............... Every 500 hours
Inspect air filter ............... Every 100 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) ................ 4.3307-4.3323 (110.000-110.040)
Crankshaft Journal Outside Diameter, in (mm) ................ 3.4642-3.4650 (87.990-88.010)
Crank Pin Outside Diameter, in (mm) ................ 2.9524-2.9531 (74.990-75.010)
Crankshaft End Play, in (mm) ................ 0.0030-0.0130 (0.070-0.320)
Intake Valve Stem Outside Diameter, in (mm) ................ 0.3126-0.3134 (7.940-7.960)
Exhaust Valve Stem Outside Diameter, in (mm) ................ 0.3118-0.3126 (7.920-7.940)
Intake Valve Guide Inside Diameter (Installed), in (mm) ................ 0.3146-0.3161 (7.990-8.030)
Exhaust Valve Guide Inside Diameter (Installed), in (mm) ................ 0.3146-0.3161 (7.990-8.030)
Intake Valve Stem to Guide Clearance, in (mm) ................ 0.0012-0.0035 (0.030-0.090)
Exhaust Valve Stem to Guide Clearance, in (mm) ................ 0.0020-0.0043 (0.050-0.110)
Intake Valve Spring Free Length, in (mm) ................ 2.441 (62.00)
Exhaust Valve Spring Free Length, in (mm) ................ 2.441 (62.00)
Intake Cam Height, in (mm) ................ 2.6322 (66.857)
Exhaust Cam Height, in (mm) ................ 2.5855 (65.671)
Piston Pin Outside Diameter, in (mm) ................ 1.5745-1.5748 (39.993-40.000)
Piston Pin to Piston Bore Clearance, in (mm) ................ 0.0003-0.0011 (0.008-0.027)
Second Ring Side Clearance, in (mm) ................ 0.0024-0.0043 (0.060-0.110)
Oil Ring Side Clearance, in (mm) ................ 0.0016-0.0035 (0.040-0.090)
Top Ring End Gap, in (mm) ................ 0.0138-0.0217 (0.350-0.550)
Second Ring End Gap, in (mm) ................ 0.0236-0.0315 (0.600-0.800)
Oil Ring End Gap, in (mm) ................ 0.0098-0.0217 (0.250-0.550)

Tightening Torque Specs

Cylinder Head Bolts ............... 160 Nm (118 lb-ft)
Main Bearing Cap Bolts (Vertical) ............... 190 Nm (140 lb-ft)
Main Bearing Cap Cross Bolts ............... 75 Nm (55 lb-ft)
Connecting Rod Bolts ............... 120 Nm (89 lb-ft)
Flywheel Housing-to-Block Bolts ............... 75 Nm (55 lb-ft)
Flywheel-to-Crankshaft Bolts ............... 115 Nm (85 lb-ft)
High-Pressure Oil Pump Mounting Bolts ............... 50 Nm (37 lb-ft)
Oil Pan Bolts ............... 27 Nm (20 lb-ft)

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• Caterpillar Engines Specs
  
• Cat 3126B Specs
  
• Cat 3126E Specs
  
• Cat 3176 Specs
  
• Cat 3176B Specs
  
• Cat 3176C Specs
  

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