Finding the Right Replacement Engine for the Caterpillar 112F Grader

[MikePhua]

The Historical Backbone of the 112F Motor Grader
The Caterpillar 112F motor grader was part of a lineage that helped shape mid-20th century road construction and maintenance. Produced during the late 1960s and early 1970s, the 112F was designed for precision grading, ditch shaping, and rural road upkeep. Caterpillar Inc., founded in 1925, had already established dominance in the earthmoving sector, and the 112F was a continuation of its commitment to durable, operator-friendly machines.
The 112F featured mechanical direct-drive transmission, hydraulic blade controls, and a robust frame capable of handling rough terrain. Its popularity extended across North America, with thousands of units deployed in county fleets, forestry roads, and mining access routes. By the mid-1970s, Caterpillar had sold over 20,000 graders in the 100-series family, with the 112F being a standout for its balance of power and simplicity.
Terminology Annotation

• Direct Drive: A transmission system where engine power is transferred directly to the drivetrain without torque converters, offering better fuel efficiency and mechanical simplicity.
  
• Serial Number Prefix: A code used by Caterpillar to identify model variants and production batches; for example, “89J” refers to a specific configuration of the 112F.
  
• 3304 Engine: A naturally aspirated 4-cylinder diesel engine produced by Caterpillar, known for its reliability and widespread use in graders, loaders, and generators.
  
• Engine Arrangement Number: A unique identifier that specifies the configuration of an engine, including fuel system, cooling setup, and mounting points.
  

Identifying the Correct Engine Model
The 112F with serial number prefix 89J likely came equipped with a Caterpillar 3304 engine, specifically the 78P variant introduced in 1968. This engine was a workhorse in its time, delivering around 85–95 horsepower depending on configuration. It featured mechanical fuel injection, wet-sleeve cylinders, and a gear-driven camshaft.
To confirm engine compatibility:

• Cross-reference the machine’s serial number with Caterpillar’s historical parts manuals
  
• Inspect the engine block for casting numbers or arrangement tags
  
• Compare mounting points and bellhousing dimensions with known 3304 configurations
  
• Verify the cooling system layout (side-mounted radiator vs. front-mounted)
  

If the original engine is missing or unidentifiable, sourcing a replacement requires careful matching of the flywheel housing, oil pan shape, and accessory drive locations.
Sourcing a Replacement Engine
Finding a 3304 engine for a vintage 112F can be challenging but not impossible. Options include:

• Salvage yards specializing in dismantled Caterpillar equipment
  
• Online marketplaces listing rebuilt or core engines
  
• Reputable remanufacturers offering zero-hour rebuilds with warranty
  
• Cross-application swaps from other machines using the same engine block
  

When purchasing a used engine:

• Request compression test results and oil analysis
  
• Inspect for freeze damage, especially in northern climates
  
• Confirm that the fuel pump and injectors match the grader’s throttle linkage
  
• Ask for the engine arrangement number to ensure compatibility
  

A Story from the Field
In 2021, a grader operator in North Carolina inherited a 112F from a retired county fleet. The machine had sat idle for years, and its engine was missing. After researching serial numbers and consulting with a retired CAT technician, he confirmed the original engine was a 3304 direct-drive variant. He located a donor engine from a decommissioned CAT 920 loader, rebuilt it with new sleeves and bearings, and successfully installed it in the grader. The machine returned to service grading private roads and driveways, proving the enduring value of legacy equipment when paired with mechanical know-how.
Industry Trends and Engine Restoration
As emissions regulations tighten, older mechanical engines like the 3304 are being phased out in new equipment. However, they remain popular in restoration circles due to their simplicity and rebuildability. In 2024, several aftermarket suppliers began offering reproduction parts for legacy CAT engines, including cylinder kits, fuel pumps, and gasket sets.
Meanwhile, some operators are retrofitting electronic engines into older frames, using adapter plates and custom wiring harnesses. While this offers improved fuel efficiency and diagnostics, it requires significant modification and may not suit purists seeking historical accuracy.
Preventative Maintenance for Legacy Engines
To extend the life of a rebuilt or replacement 3304:

• Change oil every 250 hours using SAE 15W-40 diesel-rated oil
  
• Replace fuel filters every 100 hours and bleed air from the system
  
• Monitor coolant levels and flush annually to prevent corrosion
  
• Adjust valve lash every 500 hours to maintain performance
  
• Keep spare injector nozzles and glow plugs on hand for field repairs
  

Conclusion
Replacing the engine in a Caterpillar 112F grader demands attention to serial numbers, mounting compatibility, and historical engine variants. The 3304 remains the most likely candidate, offering a blend of durability and mechanical simplicity. With careful sourcing and methodical installation, operators can revive these classic machines and keep them working for decades to come. Whether grading rural roads or restoring vintage iron, the legacy of the 112F lives on through its engine—and the people who keep it running.