Identifying the Bobcat 843 Engine and Its Mechanical Legacy

[MikePhua]

The Bobcat 843 and Its Place in Skid-Steer History
The Bobcat 843 was introduced in the 1980s as part of Bobcat’s expanding lineup of mid-sized skid-steer loaders. At the time, Bobcat—originally founded in 1947 in North Dakota—was already a dominant force in compact equipment, having pioneered the skid-steer concept decades earlier. The 843 was designed to bridge the gap between smaller utility loaders and larger construction-grade machines, offering a balance of power, lift capacity, and maneuverability.
With a rated operating capacity of 1,700 pounds and a tipping load of 3,400 pounds, the 843 was well-suited for landscaping, light demolition, and agricultural tasks. Its radial-lift boom provided excellent reach at mid-height, making it ideal for loading trucks and handling pallets. Thousands of units were sold across North America and Europe, and many remain in service today thanks to their mechanical simplicity and rugged build.
Engine Identification and Specifications
The original engine powering the Bobcat 843 was the Isuzu 4JB1-PK01—a naturally aspirated, vertical inline four-cylinder diesel. This 2.8-liter engine delivered approximately 54 horsepower and was known for its reliability and fuel efficiency. Key specifications include:

• Displacement: 169 cubic inches (2.8 liters)
  
• Aspiration: Naturally aspirated
  
• Cooling: Liquid-cooled
  
• Fuel system: Direct injection with Bosch-type pump
  
• Governor: Mechanical
  
• Lubrication: Pressure-fed with external oil filter
  
• Air intake: Dry element air cleaner
  
• Charging system: Alternator-based
  

The 4JB1 engine was widely used in industrial and agricultural applications, including forklifts, generators, and compact tractors. Its reputation for cold-weather starting and low-end torque made it a favorite among operators in northern climates.
Common Identification Challenges
Identifying the engine in an older Bobcat 843 can be tricky, especially if the machine has undergone repairs or engine swaps. Over the years, some units were retrofitted with Perkins or Kubota engines due to availability or personal preference. In such cases, visual inspection and serial number tracing become essential.
To confirm engine type:

• Locate the engine serial plate, typically mounted on the valve cover or block
  
• Cross-reference with Bobcat service manuals or Isuzu engine charts
  
• Check for distinctive features such as injector pump type, oil filter location, and intake manifold shape
  

One restorer in Michigan discovered that his 843 had been retrofitted with a Kubota V2203 engine, which required custom mounts and modified throttle linkage. While the swap worked mechanically, it complicated parts sourcing and service procedures.
Hydrostatic Drive and Hydraulic System Overview
The Bobcat 843 uses a single-speed hydrostatic transmission with four-wheel drive. This system relies on hydraulic pumps and motors to deliver torque to each wheel independently, allowing for zero-radius turning and precise control.
Hydraulic system specifications include:

• Pump capacity: 16.2 gallons per minute
  
• System pressure: 2,400 psi
  
• Hydraulic type: Open center with gear pump
  
• Loader boom: Radial-lift configuration
  

The hydrostatic drive is sensitive to fluid cleanliness and hose integrity. Regular filter changes and inspection of drive chains are essential to prevent cavitation and loss of traction. Operators often report that worn drive chains or low fluid levels result in sluggish movement or uneven wheel response.
Maintenance Tips and Engine Longevity
To keep the Isuzu 4JB1 engine running smoothly, follow these maintenance guidelines:

• Change engine oil every 100 hours using 15W-40 diesel-rated oil
  
• Replace fuel filters every 250 hours to prevent injector clogging
  
• Inspect air filter monthly and replace if contaminated
  
• Check coolant levels and flush system annually
  
• Adjust valve lash every 500 hours for optimal combustion
  

Use OEM or high-quality aftermarket parts to maintain performance. Avoid mixing hydraulic fluids or using unapproved coolants, as these can degrade seals and cause overheating.
Stories from the Field
One operator in Alberta shared a story of his 843 surviving a winter freeze after being left outside during a blizzard. Despite sub-zero temperatures, the Isuzu engine started after a few cranks, thanks to its mechanical injection and robust glow plug system. He later installed a block heater and battery blanket to prevent future cold-start issues.
Another contractor in Georgia rebuilt his 843 after discovering a cracked cylinder head. He sourced a replacement from a forklift salvage yard and completed the swap in two days. The machine returned to service clearing brush and grading driveways, proving the resilience of the platform.
Modernization and Retrofit Options
While the Bobcat 843 is no longer in production, many owners choose to modernize their machines with upgrades such as:

• LED work lights for improved visibility
  
• Quick-attach couplers for faster attachment changes
  
• Digital hour meters and temperature gauges
  
• Upgraded seat and operator controls for comfort
  

Some retrofit kits allow for installation of newer engines, but these require careful alignment and compatibility checks. Always consult with a technician before attempting major modifications.
Conclusion
The Bobcat 843 remains a symbol of durable, no-nonsense engineering. Its Isuzu 4JB1 engine, hydrostatic drive, and radial-lift boom make it a versatile tool for a wide range of tasks. Identifying and maintaining the original engine ensures continued performance and reliability. Whether restoring a barn find or keeping a daily workhorse in top shape, the 843 offers a rewarding blend of mechanical simplicity and operational capability.