Cummins NH855 Engine Parts for Australia - Engine Overhaul Kit Section

Cummins NH855 Engine Overhaul Kits and Related Components

The Cummins NH855 engine has long been recognized as a workhorse in both industrial and marine applications. Known for its rugged durability, simplicity of design, and support for rebuildability, it remains a favorite among fleets, engine shops, and maintenance facilities worldwide. Whether you’re overhauling your NH855 to extend its service life, improve fuel efficiency, or restore lost performance, choosing the right overhaul kit and supporting components is critical.

Diesel Pro Power supports thousands of customers annually with top-tier rebuild solutions. Below, we detail the overhaul kits available for the Cummins NH855 and why complementary parts and tools play an essential role in a successful engine rebuild.

Understanding the Cummins NH855 Platform

The Cummins NH855 is part of the 855 cubic inch engine family, a large-bore inline-six platform originally developed in the 1950s. Over the decades, it evolved into many variants—including the NT855, NTA855, and Big Cam models—each introducing refinements in fuel delivery, emissions control, and horsepower.

The NH855 was primarily mechanical and features gear-driven components, robust liners, and wet-sleeve design—all ideal for rebuilds and long-term maintenance. Rebuilding an NH855 offers significant cost savings over replacement, particularly for high-hour units in marine propulsion, industrial generators, oilfield applications, and legacy equipment where repower isn’t an option.

Overhaul Kits for Cummins NH855

All Cummins NH855 overhaul kits sold by Diesel Pro Power are built to OEM specifications or better. Kits vary by compression ratio and CPL (Control Parts List) number, ensuring the right fit for your specific engine build.

Overhaul Kit – 14.0:1 Compression Ratio

This kit is compatible with dozens of CPLs, including 449, 481, 500, 510, 531, 554, and many others. The 14.0:1 compression ratio was commonly used in high-performance variants of the NH and NT855 engines and is ideal for applications requiring balanced power and thermal efficiency.

Compression Ratio Meaning: A 14.0:1 compression ratio means the engine compresses air and fuel into a space 1/14th its original volume before ignition. This high compression allows for more complete combustion, delivering stronger torque and better fuel economy—but requires good cooling and quality fuel to prevent knock.

This rebuild kit includes:

• Pistons and liners with 14.0:1 configuration

• Piston rings, pins, and retainers

• Cylinder head gasket set

• Lower gasket set

• Main and rod bearings (in standard or oversize options)

• Thrust washers

Overhaul Kit – 14.5:1 Compression Ratio

Compatible with an even broader range of CPLs—including early-generation builds—this kit is optimal for operators who need slightly higher compression for improved torque and cold-start behavior. The 14.5:1 ratio is frequently found in heavy-duty NH855 units used in cold-weather climates, power generation, and constant-load applications.

This compression ratio provides:

• Slightly more efficient combustion

• Improved fuel atomization at lower RPMs

• Reduced cranking times in cold starts

This kit includes the same core components with piston domes tailored for 14.5:1 compression.

Overhaul Kit – 17.0:1 Compression Ratio

This higher-compression overhaul kit is compatible with select CPLs like 838, 840, and 1187. A 17.0:1 compression ratio was typically used in specialized versions of the 855 platform designed for extreme efficiency or altitude compensation.

Advantages of High Compression:

• Lower emissions due to more complete burn

• Higher thermal efficiency

• Suitable for turbocharged applications where airflow is abundant

However, rebuilders should ensure all surrounding systems—especially cooling and fuel injection—are in good shape before installing a high-compression kit.

Supporting Components That Improve the Rebuild Process

While an overhaul kit forms the foundation of any rebuild, several ancillary components and tools significantly improve both short- and long-term reliability.

Piston Cooling Nozzles for NH855 and NT855

Every 855 rebuild should involve checking and, if necessary, replacing the piston cooling nozzles. These small but vital parts spray oil onto the underside of the piston crown to dissipate heat.

• Requires six nozzles per engine

• Includes O-ring seals

• Ensures thermal regulation and prevents piston damage in high-load operation

Neglecting these components can lead to hot spots on the piston, ring sticking, or even engine knock under heavy load.

Feeler Gauge (.002" to .025")

After your rebuild, valve lash must be calibrated precisely. Diesel Pro Power carries feeler gauges designed specifically for the NH855 platform.

• Helps dial in valve clearance for optimal compression and combustion

• Prevents premature valve seat wear and loss of power

• Essential for both intake and exhaust adjustments

Investing in proper calibration tools minimizes future downtime and ensures a quiet, balanced engine.

Filters to Support the Freshly Rebuilt Engine

Your rebuilt engine will only be as clean and reliable as the filtration that protects it. Replacing all oil and fuel filters is non-negotiable after a rebuild.

Fuel Filters

We offer direct-fit fuel filters for the NH855 in standard and water-separating variants:

• 2.813" to 4.65" diameters

• Multiple thread sizes for different fuel housing types

• Designed to trap sediment, microbial buildup, and rust flakes

Water separators are especially important for marine installations or where fuel storage tanks may accumulate condensation.

Oil Filters

Protect the new internal components of your rebuild with high-efficiency oil filters. These are designed to:

• Remove metal wear particles during the engine break-in period

• Maintain optimal oil pressure

• Preserve piston ring and bearing surface integrity

All filters sold by Diesel Pro Power meet or exceed OEM filtration specs.

Engine Tools That Streamline Reassembly

Your NH855 rebuild will go faster and more precisely with the right tools:

Piston Ring Assembly Tool

Avoid damaging piston rings or scoring liners during installation. This tool ensures rings are compressed correctly and evenly across the piston skirt.

• Works with multiple Cummins and Detroit Diesel engines

• Reduces chance of broken rings

• Speeds up cylinder prep

Oil and Fuel Filter Wrenches

Remove or install filters without over-tightening or stripping threads. These adjustable wrenches are ideal for:

• 3-7/16" to 5-5/32" filters

• Tight spaces and marine engine rooms

• Shops performing multiple rebuilds per year

Thermostats for NH855 and NT855 Engines

Rebuilding an engine is a great time to replace the thermostat, especially on older models that may have weak or slow-opening units.

• 180°F option for standard NH855

• 185°F option for Big Cam variants

• Helps stabilize operating temperature

• Improves combustion and fuel efficiency

A stuck thermostat can undo the gains of a rebuild by causing overheat conditions or uneven warm-up.

Radiator Cleaner

Don’t overlook the cooling system. Diesel Pro Power’s radiator cleaner helps eliminate scale, rust, and sludge that can affect thermal regulation in a freshly rebuilt engine.

• Safe for copper, brass, and aluminum components

• Recommended after cylinder head replacement or liner work

• Improves flow through narrow coolant passages

Temperature Switch

This vital sensor monitors coolant temperatures and is essential for engines paired with alarms or shut-down systems.

• Closes at 205°F

• 1/2" NPT thread

• Compatible with NH855, NT855, and other Cummins platforms

Pair it with mechanical or electric gauges to prevent overheating events.

Mechanical and Electrical Gauges

After an overhaul, monitoring oil pressure, water temperature, and boost levels is critical. Diesel Pro Power provides:

• Mechanical gauges for analog reliability

• Electrical gauges in 12V and 24V for compatibility with modern panels

• Gauges with alarms for fleet or safety-critical operations

Add these during the rebuild to avoid multiple tear-downs later.

Why Choose Diesel Pro Power for Your NH855 Rebuild?

With over 40,000 satisfied customers worldwide, Diesel Pro Power is a trusted leader in diesel engine parts for Cummins and beyond. When it comes to the NH855 platform, we don’t just sell overhaul kits—we support full rebuilds with:

• Fast global shipping

• Expert customer service

• Detailed product compatibility by CPL

• Supporting components from filters to tools

Whether you’re servicing a genset in Alaska or a dredge in Central America, we provide reliable components that keep your operation running smoothly.