Reviving a Cummins NH 262-220 After Water Intrusion and Bottom-End Inspection

[MikePhua]

The NH Series and Cummins’ Mid-Century Diesel Legacy
The Cummins NH 262-220 is part of the legendary NH series, a family of inline six-cylinder diesel engines that powered trucks, industrial machines, and construction equipment from the 1950s through the 1980s. Known for their mechanical simplicity and robust torque curves, NH engines were widely used in vocational trucks and off-road applications. The “262” refers to the horsepower rating, while “220” often denotes a variant or earlier rating in the same block family.
Cummins, founded in 1919, built its reputation on engines like the NH, which featured direct injection, gear-driven accessories, and a dry sleeve cylinder design. These engines were designed to be rebuilt in the field, with modular components and generous tolerances. Despite their age, many NH units remain in service today, especially in vintage trucks and restoration projects.
Water Intrusion and Crankcase Contamination
The engine in question had sat idle for over a year, exposed to water ingress that filled the crankcase and overflowed through the right accessory drive. Water intrusion into a diesel engine is a serious concern, as it can lead to rusted bearings, seized pistons, and pitted journals.
Key terminology:

• Accessory drive: A gear-driven assembly that powers components like the air compressor or hydraulic pump.
  
• Crankcase: The lower part of the engine housing the crankshaft and connecting rods.
  
• Bearing cap: A bolted cover that secures the crankshaft bearings in place.
  
• End play: The axial movement of the crankshaft within its bearings.
  
• Side play: The lateral movement of connecting rods on the crank pins.
  

Inspection revealed waterlines on the crankshaft and block, but no sludge or mud—suggesting clean water exposure rather than contaminated runoff. This distinction matters: clean water may cause surface rust but is less likely to embed abrasive particles.
Initial Assessment and Loosening Strategy
The crankshaft was initially seized, but after inspection, all rods were found to be free, and the crank rotated with expected end play. This ruled out major bearing seizure and pointed toward surface corrosion rather than mechanical lockup.
Recommendations:

• Remove bearing caps and inspect journals for pitting or scoring
  
• Use penetrating oil and manual rotation to loosen stuck components
  
• Avoid forced cranking until lubrication is restored
  
• Inspect camshaft and roller followers for rust or galling
  
• Replace all seals exposed to water, especially accessory drive seals
  

One technician in Oklahoma shared a similar case where a Cummins NH sat submerged for months. After draining, flushing, and replacing the bearings, the engine ran with minimal smoke and full oil pressure.
Turbocharger Condition and Replacement
The T-50 turbocharger was removed and found to be seized beyond repair. Turbo failure after water exposure is common, especially if the turbine housing traps moisture and corrodes the shaft bearings.
Solutions:

• Replace turbo with OEM or remanufactured unit
  
• Flush oil feed and return lines to remove debris
  
• Prime turbo with clean oil before startup
  
• Inspect exhaust manifold for cracks or rust flakes
  
• Consider upgrading to a more efficient turbo if application allows
  

One restorer in Georgia replaced his T-50 with a Holset HX35, gaining better spool response and lower EGTs during hill climbs.
Pre-Lube System and Safe Crank Preparation
Before attempting to start the engine, it’s critical to pressure-feed oil into the system. This prevents dry starts and protects cam lobes, lifters, and crank journals.
Pre-lube method:

• Connect external oil pump between oil filter housing and pump inlet
  
• Use SAE 15W-40 diesel-rated oil with high zinc content
  
• Rotate crank manually during pre-lube to distribute oil
  
• Lube camshaft and rollers with assembly grease
  
• Monitor oil pressure gauge during crank attempt
  

One operator in Pennsylvania used a converted fuel pump as a pre-lube system, feeding oil through the filter base while rotating the engine with a breaker bar. After 20 minutes, the engine cranked smoothly and fired on ether.
Final Checks and Startup Strategy
Before startup:

• Replace all fluids—engine oil, coolant, and fuel
  
• Inspect injectors for rust or clogging
  
• Bleed fuel system and verify lift pump operation
  
• Check valve lash and timing marks
  
• Install new filters and monitor for leaks
  

Startup sequence:

• Crank with fuel disabled to build oil pressure
  
• Enable fuel and crank again with minimal throttle
  
• Listen for abnormal knocks or bearing rumble
  
• Monitor oil pressure, coolant temp, and exhaust color
  
• Run at low RPM for 30 minutes before loading
  

One fleet in Alberta revived a Cummins NH that had sat for 12 years. After a full teardown and reseal, the engine powered a gravel truck for another 5,000 hours before retirement.
Conclusion
Reviving a Cummins NH 262-220 after water exposure is a blend of mechanical intuition and methodical inspection. These engines were built to endure, and with careful attention to lubrication, bearing condition, and turbo health, they can return to service even after prolonged dormancy. In the world of vintage diesel iron, patience and precision are the keys to resurrection—and every successful startup is a tribute to the engine’s enduring design.