Reviving a P&H 312 Excavator with Custom-Fabricated Drive Components

[MikePhua]

The Legacy of P&H in Excavator Design
Pawling & Harnischfeger, better known as P&H, was a pioneering American manufacturer of heavy machinery, particularly in the mining and lifting sectors. Founded in Milwaukee in the late 19th century, P&H became synonymous with rugged, purpose-built equipment. While most of their fame came from cranes and shovels, the company also produced a line of hydraulic excavators, including the P&H 312—a mid-sized crawler excavator built for general construction and utility work.
The 312 model, likely manufactured in the late 1960s or early 1970s, featured a mechanical track drive system powered by a chain and sprocket assembly. Unlike modern hydrostatic drives, this setup relied on a direct mechanical linkage between the engine and the track sprockets, making it simpler to maintain but more prone to wear in high-load environments.
Common Wear Points in the Track Drive System
As with many older chain-driven excavators, the P&H 312’s track drive system includes a drive shaft, bushings, and a chain sprocket that transfers torque to the track sprocket. Over time, these components are subject to:

• Bushing wear due to rotational friction and lack of lubrication
  
• Sprocket tooth erosion from chain tension and misalignment
  
• Shaft fatigue from shock loads and uneven terrain
  
• Corrosion from environmental exposure
  

When these parts degrade, the excavator may exhibit symptoms such as track slippage, uneven movement, or complete loss of drive on one side. In older machines, sourcing OEM parts becomes nearly impossible, prompting owners to consider fabrication or salvage options.
Fabrication Strategies for Obsolete Components
Given the age of the P&H 312 and the unavailability of factory parts, fabrication becomes the most viable path forward. Experienced welders and machinists can replicate worn bushings and sprockets using modern materials and techniques.
Recommended approaches include:

• Measuring the original bushing dimensions and machining replacements from bronze or hardened steel
  
• Plasma cutting new sprockets from high-strength plate steel, followed by flame hardening or induction hardening of the teeth
  
• Using keyed shafts and locking collars to secure drive components
  
• Installing grease fittings or oil ports to extend service life
  

If the sprocket is a flat plate design, it can be replicated with relative ease. More complex sprockets may require CNC machining or waterjet cutting, depending on tooth profile and mounting geometry.
Sourcing Support and Technical Data
While P&H no longer supports these machines directly, some legacy documentation may still exist through industrial archives or enthusiast networks. In rare cases, contacting Komatsu Mining (which absorbed P&H’s mining division) may yield technical drawings or specifications, though parts are unlikely to be stocked.
Alternative sources include:

• MinnPar, a supplier specializing in obsolete construction equipment parts
  
• Salvage yards with inventory from the 1960s–1980s
  
• Online forums and restoration groups focused on vintage iron
  
• Custom fabrication shops with experience in agricultural or industrial machinery
  

Operators should document all measurements, including shaft diameter, sprocket pitch, and bushing clearance, before commissioning any fabrication work.
Field Anecdotes and Restoration Successes
One technician recalled working on a fleet of P&H H418 excavators, each with similar chain-driven track systems. When sprockets wore out, they were rebuilt using weld overlays and ground to shape with a die grinder. Though not factory-perfect, the repairs held up for years under moderate use.
Another operator restored a P&H 1250 with a modern hydraulic drive retrofit, replacing the chain system entirely. While this approach is costly and complex, it demonstrates the adaptability of older machines when paired with modern components.
Preventative Maintenance for Chain-Driven Excavators
To extend the life of a restored P&H 312:

• Lubricate bushings and chain links regularly with high-viscosity oil
  
• Monitor sprocket alignment and chain tension monthly
  
• Avoid high-speed travel over rocky terrain
  
• Inspect welds and fasteners after heavy use
  
• Keep the undercarriage clean to prevent abrasive wear
  

Installing a chain guard or debris shield can also reduce exposure to mud and gravel, which accelerates wear.
Conclusion
The P&H 312 excavator may be a relic of a bygone era, but its mechanical simplicity and robust design make it a candidate for restoration rather than retirement. With OEM parts long gone, fabrication offers a practical and often superior solution. By combining field ingenuity with modern materials, operators can breathe new life into these machines and preserve a piece of American heavy equipment history. Whether for light-duty work or as a collector’s project, the 312 still has stories to tell—and ground to move.