Replacing the Yanmar 4TN82 Engine in a Mustang 940 Skid Steer

[MikePhua]

The Mustang 940 and Its Role in Compact Equipment History
The Mustang 940 skid steer loader was part of Mustang Manufacturing’s push into the compact equipment market during the 1990s. Mustang, founded in 1865 and later acquired by Manitou Group, became known for producing durable, mid-sized skid steers suited for agriculture, landscaping, and light construction. The 940 model featured a rated operating capacity of around 1,500 pounds and was powered by the Yanmar 4TN82 diesel engine—a naturally aspirated four-cylinder known for its reliability and fuel efficiency.
By the early 2000s, Mustang had sold tens of thousands of skid steers globally, with the 940 becoming a popular choice in Europe and North America due to its simplicity and ease of maintenance. However, as these machines aged, engine replacement became a common challenge, especially in regions where Yanmar parts were scarce.
Challenges of Replacing the Original Yanmar Engine
The Yanmar 4TN82AS engine, while robust, is not always easy to source—particularly in markets like Greece, where parts availability is limited. When the original engine suffers extensive wear or catastrophic failure, rebuilding may not be feasible. In such cases, replacing the engine with a different brand becomes a practical solution.
Key challenges include:

• Matching engine dimensions and mounting points
  
• Aligning the flywheel and bell housing with the hydrostatic drive
  
• Ensuring compatibility with the cooling system and exhaust routing
  
• Adapting throttle and electrical connections
  
• Preserving weight balance and center of gravity
  

The Mustang 940’s engine bay is compact, and the hydrostatic pump is directly coupled to the engine flywheel. Any replacement must maintain precise alignment to avoid premature pump wear or vibration.
Evaluating Alternative Engine Options
Several engine brands offer potential replacements for the Yanmar 4TN82AS, including:

• Kubota V2203 or D1703
  Widely available and compact, Kubota engines are known for smooth operation and parts support. The V2203 offers similar horsepower and torque, though mounting brackets may require fabrication.
  
• Perkins 404D-22 or 403D-15
  Perkins engines are common in agricultural and industrial equipment. Their modular design allows easier adaptation, but the intake and exhaust may need rerouting.
  
• Isuzu 4LE1 or 3LD1
  Isuzu’s compact diesel engines are durable and often found in forklifts and generators. Their bell housing patterns differ from Yanmar, so custom adapters may be necessary.
  
• Deutz D2011 or BF4M2011
  Air-cooled options like Deutz simplify the cooling system but may require changes to the engine bay airflow and shielding.
  

When selecting a replacement, consider:

• Horsepower range: 35–45 HP
  
• Torque curve compatibility with hydrostatic drive
  
• Engine weight and vibration characteristics
  
• Availability of service parts and local support
  

Fabrication and Installation Considerations
Engine swaps in skid steers are not plug-and-play. Key fabrication tasks include:

• Building custom engine mounts using steel plate and vibration isolators
  
• Machining or adapting the flywheel to match the pump coupler
  
• Extending or rerouting fuel lines and throttle cables
  
• Modifying the exhaust system to clear the loader arms and cab
  
• Rewiring the alternator, glow plugs, and starter circuits
  

In one documented case, a technician replaced a failed Yanmar engine with a Kubota V2203 sourced from a decommissioned generator. He fabricated new mounts, adapted the flywheel with a spacer ring, and installed a remote oil filter to clear the frame. The machine ran smoothly after minor throttle linkage adjustments.
Cooling System Adaptation
If the replacement engine uses a different radiator configuration, cooling must be addressed:

• Use a radiator with similar core size and flow rate
  
• Install an electric fan if belt-driven clearance is limited
  
• Ensure proper coolant hose routing and overflow tank placement
  
• Monitor operating temperature during initial use
  

Some operators opt for oversized radiators to improve cooling in hot climates or heavy-duty applications. However, this may require cutting or relocating sheet metal panels.
Legal and Safety Implications
Engine swaps may affect emissions compliance, especially in regulated markets. While older machines like the Mustang 940 are often exempt from Tier 4 standards, it’s important to:

• Verify local regulations regarding engine replacement
  
• Maintain proper labeling and documentation
  
• Ensure that safety features like engine shutoff and throttle response remain functional
  

In some regions, insurance coverage may require disclosure of major modifications. Always document the swap and retain receipts for parts and labor.
Stories from the Field
A farmer in northern Greece faced a similar dilemma when his Mustang 940’s Yanmar engine failed. Unable to source a replacement locally, he installed a Perkins 404D-22 from a retired telehandler. After fabricating mounts and adapting the flywheel, the machine returned to service with improved fuel economy and quieter operation.
Another operator in rural Texas swapped in a Kubota D1703 and reported better cold starts and smoother throttle response. He noted that the hardest part was aligning the pump coupler, which required precision machining and trial fits.
Conclusion
Replacing the Yanmar 4TN82AS engine in a Mustang 940 is a complex but achievable task. With careful planning, fabrication, and attention to compatibility, alternative engines like Kubota, Perkins, or Isuzu can restore functionality and extend the life of the machine. While not without challenges, a successful swap can transform a sidelined skid steer into a reliable workhorse once again. The key lies in understanding the mechanical interfaces, sourcing quality components, and executing the installation with precision.