Case 680E Backhoe: Evaluating a Cummins 6BT Engine Swap

[MikePhua]

Introduction
The Case 680E backhoe loader, a robust machine from the 1980s, was originally equipped with the Case 336BD diesel engine. While the 680E remains a capable platform, its factory engine has earned a reputation for being unreliable, rare, and expensive to replace. This article explores the feasibility of swapping the original engine with a Cummins 6BT, a widely available and proven powerplant. Through technical analysis, terminology clarification, and field anecdotes, we’ll examine the challenges and opportunities of this conversion.
Understanding the Original Powerplant
The Case 336BD engine is a direct-injection diesel with a reputation for internal failures, including broken connecting rods and spun bearings. Its scarcity in salvage yards and high cost for remanufactured units make it a poor candidate for long-term reliability.
Terminology Clarified

• 336BD: A Case-built diesel engine used in various backhoes and tractors; known for reliability issues.
  
• 6BT: A 5.9L inline-six Cummins diesel engine, turbocharged, commonly found in trucks and industrial equipment.
  
• Bellhousing: The housing that connects the engine to the transmission or torque converter.
  
• Flexplate: A metal disc that connects the engine crankshaft to the torque converter in automatic transmissions.
  
• Torque Converter: A fluid coupling that transfers engine power to the transmission, allowing for variable speed and torque.
  

Why Consider a Cummins Swap

• Availability: The 6BT is widely available in both used and remanufactured forms.
  
• Cost: A running 6BT can be sourced for under $3,000, compared to $7,500+ for a remanufactured 336BD.
  
• Performance: Turbocharging improves performance at high altitudes, such as 6,000 feet above sea level.
  
• Reliability: The 6BT has a strong reputation for durability and long service life.
  

Challenges of the Conversion

• Bellhousing Compatibility
  The 680E’s transmission may not match the SAE #2 bellhousing used on most 6BT engines. Custom machining or sourcing from compatible models like the Case 580E or 580K may be required.
  
• Flywheel and Flexplate Fitment
  Adapting the torque converter to the Cummins flexplate requires precision machining and alignment. A machine shop may need to modify the flywheel to ensure proper engagement.
  
• Motor Mount Fabrication
  Custom mounts must be fabricated to accommodate the 6BT’s dimensions and weight distribution. While time-consuming, this is a manageable task with proper tools.
  
• Front Pump Drive
  The original 336BD drives the hydraulic pump directly from the crankshaft. Adapting this setup to the 6BT may require custom brackets or couplings.
  

Field Anecdote: Wyoming Operator’s Journey
An operator in Jackson, Wyoming purchased a clean 680E with a broken 336BD for $2,000. After calling multiple salvage yards, he found that most 336 engines were damaged or prohibitively expensive. He began researching the 6BT swap and discovered that the 680K model used the Cummins engine, suggesting a potential path forward. With access to an electric forklift and machining resources, he felt confident in tackling the conversion.
Historical Insight: Case Engine Lineage
The Case 301 and 336 engines share a block design, with differences in liner bore and injection systems. While the 301 was used in agricultural tractors like the 830, the 336 appeared in construction equipment and later evolved into larger displacement models. Unfortunately, these engines were never known for longevity, and many salvage units suffer from internal damage.
Case Study: Repowering with a 6BT
A technician in Minnesota repowered a motorhome with a 6BT removed from a commercial truck. The engine had only 40,000 miles and came with an Allison-compatible flywheel and SAE #2 bellhousing. He offered it for sale at $3,300, highlighting the affordability and versatility of the 6BT platform.
Best Practices for Engine Swaps

• Confirm bellhousing and torque converter compatibility before purchase
  
• Use engine mounts from similar Case models when possible
  
• Consult tractor pulling forums for cross-reference engine options
  
• Test-fit components before final installation to avoid clearance issues
  
• Retain usable parts from the original engine for resale or reuse
  

Anecdote: Salvage Yard Realities
Multiple salvage yards reported that they had never received a 336BD engine without a broken crank or block damage. This underscores the rarity and fragility of the original powerplant. One yard even laughed at the mention of the 336BD, calling it “a ticking time bomb.”
Conclusion
Swapping a Cummins 6BT into a Case 680E is a challenging but feasible project. While motor mounts and flywheel modifications require careful planning, the benefits of reliability, performance, and long-term support make the conversion worthwhile. For operators tired of chasing rare parts and unreliable engines, the 6BT offers a path to renewed productivity and peace of mind. With the right tools and determination, even legacy iron can be reborn with modern muscle.