Converting the Starter System on a Caterpillar No. 12 Grader

[MikePhua]

The Legacy of the No. 12 Grader and Its Starting System
The Caterpillar No. 12 motor grader, introduced in the 1930s and refined through the 1960s, became a staple in road maintenance and construction across North America. Powered by the D318 diesel engine, many units relied on a gasoline-powered pony motor to start the main engine—a common practice before electric starters became reliable for large diesel engines.
The pony motor system, while effective in its time, is now considered outdated. It requires separate fuel, ignition components, and manual operation, making cold starts and maintenance more cumbersome. As parts become scarce and reliability declines, many owners opt to convert their graders to direct electric start systems.

Starter Conversion Overview and Kit Components
Modern conversion kits for the No. 12 grader typically include:

• Gear-driven electric starter
  
• Gear-driven alternator
  
• Starter button and amp gauge
  
• Heavy-duty battery cables (usually 0-gauge)
  
• Hole saw and boring template (if starter hole is not pre-machined)
  
• Mounting bolts and cable ends
  

These kits are designed to replace the pony motor entirely, allowing the D318 engine to be started directly from battery power. Some graders already have a machined starter hole in the bell housing, simplifying installation. Others require drilling and tapping, which can be done using the provided template and hole saw.

Removing the Pony Motor and Reconfiguring the Layout
Removing the pony motor frees up space for battery placement. Many operators choose to mount the batteries in the vacated pony compartment rather than on the frame rails or axles. This centralizes weight and simplifies cable routing.
Key steps in the removal process:

• Drain coolant from the pony motor block passages
  
• Disconnect fuel and ignition lines
  
• Remove mounting bolts and lift the pony motor out
  
• Fabricate block-off plates for water passages and mounting surfaces
  
• Clean and inspect the flywheel housing for residual oil or debris
  

The oil drain from the pony motor typically passes through the flywheel housing and does not require refilling after removal. Only the coolant passages need to be sealed to prevent leaks.

Starter Fitment and Bolt Clearance Issues
Even when the starter hole is present, fitment can be tricky. Some starters require indexing the base to ensure the solenoid clears adjacent castings. In tight spaces, standard hex bolts may not fit, so 12-point bolts with reduced head profiles are recommended.
Tips for installation:

• Use a small-headed 12-point bolt for the rear mounting hole
  
• Grind a slight relief in the casting if clearance is tight
  
• Test-fit the starter before final wiring
  
• Torque bolts evenly to avoid misalignment
  

A gear-driven alternator is often installed alongside the starter to provide reliable charging. These alternators are more durable than belt-driven units and better suited for dusty or high-vibration environments.

Wiring and Battery Setup
Once mechanical components are installed, wiring becomes the next priority. The conversion typically uses two 12V batteries wired in parallel to provide sufficient cranking power. Cable routing should minimize bends and avoid heat sources.
Recommended wiring practices:

• Use 0-gauge cable for starter and ground connections
  
• Install a master disconnect switch for safety
  
• Mount the amp gauge and starter button in a weather-protected location
  
• Secure cables with clamps and protect with loom tubing
  

In hot climates, battery trays should be ventilated or insulated to prevent thermal degradation. A contractor in California reported ambient temperatures exceeding 110°F during installation, prompting the use of heat shields and elevated trays.

Fuel System and Final Checks
After the starter is installed, the fuel system must be bled to remove air introduced during downtime. Older D318 engines may use sediment bowls or inline strainers instead of modern spin-on filters.
Steps to restore fuel flow:

• Open bleed screws on injector pump and lines
  
• Crank engine until fuel flows steadily
  
• Replace or clean strainers and flush lines
  
• Check for leaks and secure fittings
  

If the engine fails to start after cranking, verify glow plug operation (if equipped), fuel delivery, and starter engagement. A weak battery or poor ground can cause slow cranking and failed ignition.

Brake System Restoration Considerations
While unrelated to the starter conversion, many owners of vintage No. 12 graders also face brake system challenges. Restoring brakes involves:

• Removing wheels and brake drums (often seized from age)
  
• Rebuilding or replacing the master cylinder
  
• Inspecting and replacing corroded brake lines
  
• Adjusting linkage and pedal travel
  

Brake access is notoriously difficult due to drum fitment and rust. Penetrating oil, heat, and patience are essential. Some operators fabricate pullers or use hydraulic presses to remove stubborn drums.

Conclusion
Converting a Caterpillar No. 12 grader from pony motor to electric start is a practical upgrade that improves reliability, simplifies operation, and reduces maintenance. With the right kit and careful installation, even decades-old machines can be brought back to life and returned to productive service. Whether grading ranch roads or restoring antique iron, the direct-start conversion is a proven path to modernizing a classic workhorse.