Restoring a Koehring 6644SK Excavator in a Post-Support Era

[MikePhua]

The Koehring Legacy and the 6644SK’s Place in Excavator History
Koehring was once a respected name in American heavy equipment manufacturing, with roots dating back to the late 19th century. Known for its cranes and excavators, the company produced rugged machines that served in construction, demolition, and scrap handling. The 6644SK excavator, likely built in the late 1980s or early 1990s, was part of Koehring’s final generation before the brand was absorbed through a series of acquisitions, eventually landing under Terex’s umbrella.
The 6644SK was a large, wheeled excavator powered by a Cummins diesel engine, featuring a robust hydraulic system and mechanical simplicity that made it popular in scrapyards and industrial sites. However, with Koehring’s exit from the market and the subsequent fragmentation of its parts inventory, sourcing components for these machines has become a challenge.
Why Parts Are So Difficult to Find
The primary issue with maintaining a Koehring 6644SK today is the lack of centralized parts support. Unlike Caterpillar or Komatsu, which maintain legacy parts databases and global dealer networks, Koehring’s inventory was scattered across regional dealers, many of which have since closed or sold off their stock.
Compounding the problem:

• The machine is over 30 years old, placing it well beyond typical OEM support timelines
  
• Many components were sourced from third-party suppliers that no longer exist
  
• Documentation is scarce, and parts manuals are often incomplete or outdated
  
• Terex, the eventual inheritor of Koehring’s assets, does not actively support the 6644SK
  

Despite these challenges, the 6644SK has one advantage: Koehring often used off-the-shelf components rather than proprietary designs. This opens the door to cross-referencing parts from other manufacturers and adapting modern equivalents.
Strategies for Sourcing and Substituting Components
Owners attempting to restore or maintain a 6644SK must rely on a combination of ingenuity, research, and community support. Key strategies include:

• Identify component manufacturers: Many hydraulic pumps, valves, and electrical parts were made by companies like Rexroth, Vickers, or Parker. Look for stamped part numbers or tags.
  
• Use visual matching: Take detailed photos of damaged or worn parts and compare them to listings on industrial surplus sites or eBay.
  
• Cross-reference with other brands: Machines from Link-Belt, Case, or even older CAT models may share similar joystick assemblies, valve blocks, or actuators.
  
• Contact rebuilders: Hydraulic shops can often fabricate seals, rebuild pumps, or machine bushings to spec.
  
• Tap into forums and salvage yards: Veteran mechanics and equipment wreckers may have leftover stock or know where to source rare parts.
  

One scrapyard operator in Pennsylvania successfully replaced a faulty joystick by matching it to a surplus unit from a Link-Belt excavator. Though not identical, the wiring and hydraulic ports aligned well enough to restore function.
Commonly Replaceable Systems and What to Watch For
While some parts are nearly impossible to find, others can be serviced or substituted with relative ease. Focus on the following:

• Engine: The Cummins powerplant is still widely supported. Filters, injectors, and rebuild kits are readily available.
  
• Hydraulics: Pumps and cylinders can be rebuilt or replaced with compatible units.
  
• Electrical: Wiring harnesses may need to be custom-built, but relays, switches, and gauges are often standard.
  
• Cab controls: Joysticks and pedals can be retrofitted from similar-era machines.
  
• Tires and wheels: If the machine is wheeled, standard industrial tires can be sourced from commercial suppliers.
  

Avoid relying on Terex for support, as their current product line does not include legacy Koehring models, and their parts departments are unlikely to stock anything relevant.
Preservation Challenges and the Value of Documentation
One of the most valuable tools in restoring a Koehring 6644SK is a complete parts manual. These documents, often scanned and shared among enthusiasts, provide exploded diagrams, part numbers, and assembly instructions. Even if the original parts are discontinued, the manual can help identify dimensions and specifications for custom fabrication.
Tips for documentation use:

• Print and laminate key pages for shop reference
  
• Use part numbers to search industrial catalogs and online marketplaces
  
• Annotate diagrams with modern equivalents as you discover them
  
• Share updated lists with other owners to build a community knowledge base
  

A mechanic in Wisconsin noted that his restoration of a 6644SK was only possible because of a scanned manual he received from a fellow operator. With it, he was able to rebuild the swing motor and replace the hydraulic control block using parts from a surplus supplier.
Conclusion
Maintaining a Koehring 6644SK excavator in today’s market is a test of resourcefulness and mechanical intuition. While OEM support has vanished, the machine’s use of standard components and durable design make restoration feasible for those willing to dig deep. By leveraging parts manuals, cross-brand compatibility, and the expertise of rebuilders and salvage networks, owners can keep these legacy machines running long after their factory support has faded. In the world of heavy equipment, some machines endure not because they’re easy to fix—but because they’re worth the effort.