The Enduring Legacy of the Cummins NH220 Diesel Engine

[MikePhua]

Cummins and the Rise of Heavy-Duty Diesel Power
Founded in 1919 in Columbus, Indiana, Cummins Engine Company quickly became a pioneer in diesel technology. By the mid-20th century, Cummins had established itself as a dominant force in powering trucks, construction equipment, and industrial machinery. The NH series, introduced in the 1950s, was part of this expansion—designed to meet the growing demand for reliable, high-torque engines in demanding environments.
The NH220, one of the most widely recognized models in the series, became a staple in logging trucks, bulldozers, and off-road haulers throughout the 1960s and 1970s. Its reputation for simplicity, durability, and field-serviceability made it a favorite among operators and mechanics alike.
Core Specifications and Mechanical Features
The NH220 is a naturally aspirated, inline six-cylinder diesel engine with a displacement of 14 liters (855 cubic inches). It produces approximately 220 horsepower at 2100 RPM and delivers robust torque at low engine speeds—ideal for heavy hauling and earthmoving.
Key mechanical features include:

• Cast iron block and head for thermal stability
  
• Mechanical fuel injection pump (PT system)
  
• Overhead valve design with pushrod actuation
  
• Wet-sleeve cylinder liners for easy rebuilds
  
• Gear-driven camshaft and accessory drives
  
• Compression ratio around 14.5:1
  

The engine’s simplicity is part of its charm. With no turbocharger, electronic controls, or emissions systems to complicate diagnostics, the NH220 can be maintained with basic tools and mechanical know-how.
Common Applications and Field Performance
The NH220 was used extensively in:

• Logging trucks and off-road haulers
  
• Bulldozers and graders from manufacturers like Clark and Allis-Chalmers
  
• Oilfield rigs and stationary pumps
  
• Marine propulsion in small tugboats and workboats
  

Its torque curve made it ideal for low-speed, high-load applications. Operators often praised its ability to “lug” through tough terrain without stalling. In one story from British Columbia, a 1968 logging truck powered by an NH220 climbed a muddy mountain pass with a full load of cedar logs—while newer turbocharged engines struggled with traction and throttle response.
Maintenance and Longevity
The NH220 is known for its long service life, often exceeding 15,000 hours between major overhauls when properly maintained. Key maintenance practices include:

• Regular valve lash adjustment every 500 hours
  
• Fuel filter changes every 250 hours
  
• Oil and coolant analysis to detect early wear
  
• Inspection of injector tips and fuel pump calibration
  
• Monitoring exhaust color for signs of ring or valve wear
  

One of the most common service tasks is replacing the cylinder head gasket, especially in engines that have overheated or been run with poor coolant. Fortunately, the NH220’s head can be removed without disturbing the block, and parts remain widely available through aftermarket suppliers.
Troubleshooting and Field Repairs
Because of its mechanical simplicity, the NH220 is highly repairable in the field. Common issues and solutions include:

• Hard starting
  • Check fuel pressure from the PT pump
    
  • Inspect for air leaks in the suction line
    
  • Verify glow plug or intake heater function in cold climates
    
• Loss of power
  • Inspect injector spray pattern
    
  • Check valve timing and cam gear wear
    
  • Test compression across all cylinders
    
• Excessive smoke
  

• Black smoke: overfueling or restricted air intake
  
• Blue smoke: oil consumption from worn rings or valve guides
  
• White smoke: unburned fuel due to poor compression or cold cylinders
  

In one case, a contractor in Montana diagnosed a power loss by using a simple infrared thermometer on each exhaust port. One cylinder was running cold—indicating a stuck injector. Replacing the injector restored full performance.
Modern Relevance and Restoration Culture
Though the NH220 is no longer in production, it remains a popular choice for restoration projects and vintage equipment rebuilds. Enthusiasts value its mechanical honesty and the satisfaction of tuning an engine without a laptop. Some even retrofit NH220s into custom-built trucks or repowered dozers for show and utility.
In 2022, a vintage equipment show in Ohio featured a fully restored Clark Michigan 275B loader with an NH220. The machine drew crowds not just for its size, but for the unmistakable sound of the engine—deep, rhythmic, and unmistakably mechanical.
Conclusion
The Cummins NH220 is more than an engine—it’s a symbol of an era when durability, simplicity, and raw torque defined heavy equipment. Its continued presence in working fleets and restoration yards speaks to its timeless design and the respect it commands among operators. Whether pulling logs through mountain passes or powering a vintage grader, the NH220 remains a testament to the enduring value of well-built diesel iron.