Buying a Used Caterpillar 120 Motor Grader with Confidence

[MikePhua]

The CAT 120 and Its Grading Legacy
The Caterpillar 120 motor grader has been a cornerstone of road construction and maintenance since its introduction in the mid-20th century. Designed for precision grading, ditch shaping, and surface finishing, the 120 series evolved through multiple generations, each improving on hydraulic control, operator comfort, and mechanical reliability. With tens of thousands of units sold globally, the CAT 120 remains one of the most recognized graders in the industry.
Earlier models like the 120G and 120H featured mechanical linkages and direct-drive transmissions, while later versions such as the 120M introduced joystick controls and electronically controlled engines. Whether you're looking at a 1980s-era machine or a post-2010 model, understanding the mechanical condition and service history is essential before purchase.
Key Inspection Points Before Purchase
When evaluating a used CAT 120, focus on the following areas:

• Articulation Joint: Check for excessive play or worn bushings. Movement beyond spec can affect grading accuracy.
  
• Circle Drive and Gear Teeth: Inspect for wear, binding, or missing teeth. Smooth rotation is critical for moldboard control.
  
• Hydraulic Cylinders: Look for leaks, scoring, and rod pitting. Rebuilding cylinders can be costly if multiple are affected.
  
• Transmission and Clutch: Test for smooth gear shifts and consistent engagement. Slipping or delayed response may indicate internal wear.
  
• Engine Compression and Blow-by: Use a compression tester and inspect the breather tube for oil vapor. Excessive blow-by suggests ring or valve wear.
  
• Tandem Axles and Final Drives: Check for oil leaks, bearing noise, and gear backlash. These components endure high torque during grading.
  
• Cab Controls and Electronics: Verify that all switches, gauges, and warning lights function. Replacement parts for older models may be limited.
  
• Tires and Rims: Inspect for sidewall cracking, tread depth, and rim damage. Grader tires are expensive and often overlooked.
  

A buyer in Alberta once purchased a 120G with a clean exterior but later discovered a cracked circle gear and leaking tandem axle seals. The repairs cost nearly 20% of the purchase price, highlighting the importance of thorough inspection.
Engine Variants and Performance Considerations
Depending on the year, the CAT 120 may be equipped with:

• CAT 3304 or 3306: Mechanical inline 4- or 6-cylinder engines known for durability and ease of service.
  
• CAT C7 or C9 ACERT: Electronic engines with emissions controls and higher fuel efficiency.
  
• Horsepower Range: Typically between 125–150 HP depending on model and configuration.
  
• Fuel Consumption: Averages 8–12 liters per hour under moderate load.
  

Mechanical engines are easier to rebuild and diagnose, while electronic engines offer better diagnostics but require specialized tools. If operating in remote areas, mechanical simplicity may be preferable.
Hydraulic System and Blade Control
The grader’s hydraulic system governs blade lift, tilt, articulation, and steering. Key components include:

• Hydraulic Pump: Gear or piston type, delivering flow to control valves.
  
• Control Valves: Manifold blocks with spool valves for each function.
  
• Blade Lift Cylinders: Dual cylinders for precise elevation control.
  
• Circle Rotation Cylinder: Powers the moldboard’s horizontal rotation.
  
• Steering Cylinder: Controls front wheel angle and responsiveness.
  

Test all blade functions under load. Delayed response or jerky movement may indicate air in the system, worn seals, or contaminated fluid. A contractor in Texas improved blade control on his 120H by flushing the hydraulic system and replacing two worn valve spools.
Operational History and Maintenance Records
Request service logs and ownership history. Key indicators of a well-maintained machine include:

• Regular oil and filter changes
  
• Documented cylinder rebuilds
  
• Transmission fluid analysis
  
• Tire replacements and alignment records
  
• Electrical system repairs or upgrades
  

Machines used in municipal fleets often have better maintenance records than those from private contractors. However, hours alone don’t tell the full story—a 10,000-hour machine with consistent service may outperform a 5,000-hour unit with neglected maintenance.
Parts Availability and Support
Caterpillar’s global support network ensures that parts for most 120 models remain available. However, older units may require:

• Sourcing from salvage yards or aftermarket suppliers
  
• Rebuilding components like pumps and cylinders
  
• Fabricating brackets or bushings for obsolete parts
  
• Upgrading electrical systems with universal components
  

A restorer in Chile rebuilt a 120G using a mix of OEM parts and locally machined bushings, restoring full functionality for rural road work.
Conclusion and Recommendations
Buying a used CAT 120 motor grader can be a smart investment if approached with diligence and mechanical awareness. These machines are built to last, but hidden wear can turn a bargain into a burden.
Recommendations include:

• Perform a full mechanical and hydraulic inspection
  
• Test all blade and steering functions under load
  
• Review engine performance and transmission behavior
  
• Request service records and verify ownership history
  
• Budget for initial repairs and upgrades post-purchase
  

With careful evaluation and a solid maintenance plan, the CAT 120 becomes more than a purchase—it becomes a precision grading tool capable of shaping roads, ditches, and landscapes for years to come.