Restoring an Allis-Chalmers HD5G Track Loader with a Detroit 2-71 Engine

[MikePhua]

The HD5G and Its Industrial Roots
The Allis-Chalmers HD5G track loader was part of a post-war wave of compact crawler machines designed for utility work, land clearing, and light construction. Introduced in the 1950s, the HD5 series was powered by the Detroit Diesel 2-71 two-cylinder engine—a rugged, high-revving powerplant known for its distinctive sound and reliability. The HD5G variant featured a front loader attachment and was often used in municipal yards, small farms, and private contracting operations.
Allis-Chalmers, founded in Milwaukee in the 19th century, was a major player in agricultural and industrial machinery. By the time the HD5G was in production, the company had already established itself in the crawler tractor market, competing with Caterpillar and International Harvester. Though production numbers for the HD5G were modest compared to larger models, its simplicity and durability earned it a loyal following.
Acquiring and Transporting a Vintage Machine
One operator recently acquired an HD5G in surprisingly good condition after years of searching. The machine was located in upstate New York and required an 850-mile round trip for transport to South Jersey. Despite its age, the Detroit 2-71 engine started easily and ran smoothly, a testament to the longevity of the two-stroke diesel design.
The Detroit 2-71, producing around 67 horsepower, was widely used in generators, marine applications, and industrial equipment. Its roots trace back to the 1930s, and its modular design allowed for easy rebuilds and parts interchangeability. The engine’s blower-driven intake system gave it a unique exhaust note and made it well-suited for cold starts and heavy-duty cycles.
Initial Inspection and Track System Issues
Upon arrival, the HD5G showed signs of wear in the undercarriage, particularly in the track adjusters and idler slide assemblies. One adjuster appeared bent, likely from a recent operation. Hydraulic lines showed minor leaks, and the track slides—metal guides that support the idlers—were worn and required attention.
Terminology and component notes:
- Track Adjuster: A hydraulic or spring-loaded mechanism that maintains track tension.
- Idler Slide: A guide rail that allows the front idler to move during track tensioning.
- Loader Arms: The steel arms connecting the bucket to the frame, actuated by hydraulic cylinders.
- Hydraulic Lines: Flexible hoses that carry pressurized fluid to actuators and valves.
The operator planned to disassemble the tracks and inspect each component, with the goal of rebuilding or fabricating replacements as needed. This approach reflects the ethos of vintage equipment restoration—where parts may be unavailable, but ingenuity fills the gap.
Restoration Strategy and Practical Recommendations
Restoring an HD5G requires a blend of mechanical skill and historical research. Recommendations include:

• Source OEM or reproduction manuals for torque specs and assembly diagrams
  
• Use high-strength steel when fabricating idler slides or adjuster brackets
  
• Replace all hydraulic hoses with modern equivalents rated for 3,000 psi
  
• Inspect track pins and bushings for wear; replace if oval-shaped or loose
  
• Flush the hydraulic system and replace filters before reassembly
  

For the Detroit 2-71:

• Use SAE 40 oil for warm climates or SAE 30 for cooler regions
  
• Check blower seals and governor linkage for proper operation
  
• Replace fuel filters and bleed the system before startup
  
• Monitor exhaust color for signs of injector imbalance or ring wear
  

Historical Anecdotes and Field Wisdom
During the 1970s, HD5G loaders were commonly seen in county road departments and small logging outfits. One retired operator recalled using an HD5G to clear snow from rural roads in Vermont, where the Detroit engine never failed to start—even in subzero temperatures. Another technician shared that the track adjusters were prone to bending if the machine was operated with loose tracks over rocky terrain.
In recent years, vintage equipment enthusiasts have begun restoring HD5Gs for show and light-duty use. Their compact size and mechanical simplicity make them ideal candidates for backyard projects and hobby farms.
Conclusion
The Allis-Chalmers HD5G track loader, powered by the Detroit 2-71, remains a symbol of mid-century industrial resilience. Restoring one is not just a mechanical task—it’s a journey into the legacy of American manufacturing. With careful inspection, fabrication, and respect for original design, the HD5G can return to work or proudly idle at a vintage machinery show. In every clatter of its two-stroke engine, there’s a reminder of the era when iron was built to last—and when every machine had a story worth telling.