Koehring 6620 LC-5 Excavator: Maintenance Challenges, Filter Crossovers, and Undercarriage Realities

[MikePhua]

Introduction: Reviving a Legacy Excavator
The Koehring 6620 LC-5, powered by an Isuzu 6BD1T turbocharged diesel engine, represents a durable yet increasingly rare breed of mid-1980s excavators. As parts become harder to source and documentation grows scarce, owners face unique challenges in maintaining these machines. This article explores the practical realities of servicing the 6620 LC-5, with a focus on filter cross-referencing, undercarriage rebuilds, and hydraulic system upkeep.
Terminology Clarification

• Hy-Dash Final Drive: A proprietary track drive system used in Koehring excavators, no longer in production.
  
• Carrier Roller: A roller mounted above the track frame that supports the upper section of the track chain.
  
• Return Hydraulic Filter: A filter that cleans hydraulic fluid returning to the reservoir, critical for system longevity.
  
• Pilot Filter: A small hydraulic filter that protects the pilot control circuit from contamination.
  
• Swing Filter: A filter dedicated to the swing motor circuit, ensuring smooth rotation of the upper structure.
  

Filter Identification and Cross-Referencing
One of the most persistent issues for Koehring 6620 LC-5 owners is identifying and sourcing replacement filters. Many original filters bear Japanese markings or obsolete part numbers, making cross-referencing difficult. However, through community collaboration and parts manual analysis, several key filters have been matched to modern equivalents:

• Engine Oil Filter: Wix 51640
  
• Fuel Filter: Wix 33260
  
• Air Filter: Donaldson P181054 (crosses from 900V6875)
  
• Hydraulic Spin-On Filter: Donaldson P550008
  
• Main Return Cartridge Filter: Donaldson P551210
  

Additional filters such as pilot, swing, and suction strainers have been identified through part number tracing and physical inspection. Some elements, like the suction strainer (730 4869), are no longer available and must be sourced from salvage or custom manufacturers.
Undercarriage Rebuilds: Bearings, Idlers, and Track Adjusters
Owners undertaking undercarriage rebuilds face a mixed bag of accessibility and cost. Upper carrier rollers, for example, use ball bearings and can be rebuilt if seals are intact. However, front idlers are notoriously difficult to source. One technician noted that Terex, the successor to Koehring, quoted exorbitant prices and struggled to locate parts.
Track adjuster grease cylinders are another common repair point. Fortunately, seals can be sourced from local hydraulic shops, and pistons are often reusable. This DIY approach reflects the broader ethos of Koehring ownership: resourcefulness over reliance.
Field Anecdote: Alaska’s Filter Frustration
An operator in Alaska attempted to change the return hydraulic filter but was stymied by the lack of cross-reference data. NAPA was unable to match the Koehring part number, and online resources were limited. Eventually, through community input and parts manual decoding, the correct Donaldson replacement was identified—highlighting the importance of peer networks in legacy equipment maintenance.
Hydraulic System Insights: Filtering and Fluid Cleanliness
Given the difficulty of sourcing filters, one owner devised a multi-stage pre-filtering system for hydraulic fluid. This setup included:

• 143-micron coarse filter
  
• 25-micron intermediate filter
  
• 10-micron fine filter
  
• Water separator with dual gauges
  

This custom-built filter cart allowed for fluid purification before reservoir filling, reducing contamination risk. The owner also explored continuous filtration using a DC pump, aiming to clean fluid during machine operation.
Historical Context: Koehring’s Transition and Legacy
Koehring excavators were once a staple in North American construction, known for their robust build and straightforward mechanics. The 6620 LC-5, produced in the mid-to-late 1980s, featured a blend of Japanese and American components. As the brand transitioned under Terex, parts support dwindled, leaving owners to rely on manuals, salvage yards, and ingenuity.
The Hy-Dash final drives, while effective, are no longer manufactured. Regular gear oil changes and seal inspections are essential to prolong their life, as replacement parts are nearly impossible to find.
Best Practices for Maintaining the 6620 LC-5

• Document Serial Numbers: Helps identify compatible parts and manuals.
  
• Cross-Reference Filters Proactively: Build a list of modern equivalents for future use.
  
• Rebuild When Possible: Carrier rollers and adjusters can often be refurbished.
  
• Use Fluid Filtration Systems: Protect hydraulic components from premature wear.
  
• Network with Other Owners: Peer advice often fills gaps left by manufacturers.
  

Conclusion: Keeping the Iron Alive
Maintaining a Koehring 6620 LC-5 is a labor of love, requiring patience, creativity, and a willingness to dig deep into parts manuals and community wisdom. While the machine may be decades old, its capabilities remain relevant—especially when paired with an operator who understands its quirks and strengths. In a world of disposable equipment, the 6620 LC-5 stands as a testament to durability and the enduring value of mechanical know-how.