Cummins NH855 Engine Parts - Piston Kit Section

Cummins NH855 Engine Parts – Piston Kit Section

The Cummins NH855 engine is a legendary workhorse known for its durability, serviceability, and legacy across industrial, marine, and heavy-duty equipment applications. Originally developed in the mid-20th century, the NH855 continues to power fleets and equipment worldwide. A key part of keeping these engines running efficiently is maintaining the integrity of the piston system. At Diesel Pro Power, we offer a full catalog of NH855 piston kits, cylinder liners, liner seals, and piston ring sets to support professional rebuilds and overhauls.

Overview of the NH855 Piston Assembly

The piston system of the Cummins NH855 is engineered to withstand high compression, extended operating cycles, and heavy-duty thermal stress. Whether you're rebuilding a naturally aspirated model or a turbocharged NT855 variant, selecting the correct piston kit is critical. Each piston kit offered here is matched to a specific Compression Pressure Level (CPL) number—Cummins' standard for identifying specific build configurations within engine families.

Key Piston Kit Attributes:

• Material Construction: Forged aluminum alloy pistons, precision-machined to exacting Cummins standards.

• Configuration: Includes piston crown and skirt, piston pin (also known as a wrist pin), and compatible compression height.

• Compatibility: Designed to meet OE compression ratios for NH and NT 855 engines across dozens of CPL variations.

Compression Ratio Options for NH855 Pistons

Different applications call for different compression ratios depending on the desired power output, fuel economy, and operating temperature range. Diesel Pro Power offers three primary compression ratio options for the Cummins NH855 engine family:

1. 14.0:1 Compression Ratio Piston Kit

This standard-duty configuration is ideal for general-purpose applications where engine longevity and balanced thermal dynamics are essential. Common among CPL numbers including 449, 481, 500, 531, and others, this kit is frequently used in:

• Marine workboats and trawlers

• Generator sets

• Agricultural tractors

• Mining equipment

This piston profile helps ensure efficient combustion while reducing stress on connecting rods and liners over time.

2. 14.5:1 Compression Ratio Piston Kit

Slightly higher in compression than the 14.0:1 version, this kit provides improved thermal efficiency and slightly higher power output. With support for over 100 CPL numbers, including some of the earliest NH configurations (CPLs 1 through 20), it is a versatile option for:

• Construction machinery

• Oilfield pump engines

• Tugboats and barges

• Vintage highway trucks still using the NH855 powerplant

This option is especially helpful for operators looking to preserve historical or legacy machines with original combustion specs.

3. 17.0:1 Compression Ratio Piston Kit

For high-performance and turbocharged applications, the 17.0:1 piston kit offers the highest compression ratio available in the NH855 series. Designed for CPLs like 838 and 1187, it delivers exceptional combustion efficiency, making it suitable for:

• Turbocharged industrial generators

• Marine propulsion systems under high load

• Extreme-duty hauling trucks

Engines using this kit must be maintained with precision to prevent excessive thermal stress, but when paired with the correct cooling and injection system, they deliver unmatched performance.

Cylinder Liners for NH855

The cylinder liner is the backbone of the piston system. Diesel Pro Power offers both standard and oversized liner options to accommodate block wear or previous rebuild work.

Standard Cylinder Liners

These are direct replacements for factory-original sleeves and are compatible with NH855 and NT855 configurations. The standard liner is ideal when the block bore remains within original specification and there is no damage or out-of-round wear.

Specifications:

• Designed for drop-in installation with standard press fit

• Compatible with all major CPL piston kits

• Works with both standard and premium ring configurations

Oversize Cylinder Liners (0.020" / 0.040")

When a block has been honed or bored due to wear or scoring, an oversized liner becomes necessary. Diesel Pro Power offers two oversize options to restore cylinder fit and compression:

• 0.020" oversize

• 0.040" oversize

These oversize liners are built with slightly larger outer diameters and designed to maintain the correct press fit and liner height. Compatible with standard NH855 pistons when the cylinder bore is corrected accordingly.

Liner Sealing Components

Installing or replacing a cylinder liner requires attention to sealing details. Diesel Pro Power provides all necessary seals to ensure coolant and oil passages remain protected.

Liner Seal Ring

Each liner requires a seal ring to seat correctly into the block. This prevents coolant and combustion gases from escaping into the engine internals. One liner seal ring is used per cylinder.

• Material: High-durability synthetic rubber

• Profile: Round or rectangular depending on block revision

• Heat tolerance: Up to 300°F continuous exposure

Liner O-Ring Seal

Each liner also requires two O-ring seals to complete the installation. These sit at the lower portion of the liner and prevent coolant leakage. When installing new liners, never reuse old O-rings.

• Sold individually; two required per cylinder

• Chemical-resistant compound

• Compatible with standard and oversize liner options

NH855 Piston Ring Sets

Replacing piston rings is critical during any rebuild, even if the piston crown is reused. Diesel Pro Power offers two main ring sets for the Cummins NH855 engine family:

Standard Ring Set

This is the go-to ring set for conventional rebuilds. It includes compression rings and oil control rings made from high-strength steel alloy with a moly-coated finish for longer service life. The standard ring set is engineered to:

• Maintain optimal compression

• Reduce oil blow-by

• Support engines with standard bore liners

Ideal for moderate-duty applications and operators looking for long-term reliability.

Premium Ring Set

The premium ring set includes upgraded materials and tighter tolerances. Often used in applications involving:

• Frequent start-stop cycles

• Long-duration high-load operation

• High-sulfur fuel environments

It features improved wear coatings and ring geometry to help seal better in engines with slightly worn liners. This ring set is frequently chosen by rebuilders who want the best protection for their investment.

Choosing the Right Piston Kit: What You Need to Know

Selecting the right piston kit for your NH855 rebuild requires a few key pieces of information:

• Engine CPL Number: This is the most reliable method for matching pistons, rings, and liners. The CPL governs compression ratio, piston crown design, and injector configuration.

• Compression Ratio Requirement: Determine whether the engine application calls for 14.0:1, 14.5:1, or 17.0:1.

• Liner Bore Condition: If the bore is within spec, standard liners and rings may be used. If out-of-round or worn, consider oversized liners and confirm compatibility.

Each kit sold by Diesel Pro Power is designed with these variables in mind and includes only components built to exacting Cummins standards.

Rebuild Kit Bundle Options (Coming Soon)

While all items are available individually, Diesel Pro Power is developing full piston rebuild bundles for the NH855 platform. These will include:

• Pistons (with pins)

• Piston ring sets

• Cylinder liners

• Liner seal rings and O-rings

Bundles will be grouped by CPL number to take the guesswork out of parts matching. Customers can expect improved convenience, bundled pricing, and the confidence of complete compatibility.

Why Choose Diesel Pro Power for NH855 Piston Components?

With over 40,000 satisfied customers globally, Diesel Pro Power is the trusted source for Cummins engine parts. Here's why technicians and fleet managers choose us for NH855 rebuilds:

• OEM-Level Quality: All pistons, rings, and liners meet or exceed original Cummins specifications.

• Same-Day Shipping: Orders placed before our cutoff time ship out the same business day.

• Knowledgeable Support: Our team can help confirm compatibility using CPL numbers or engine applications.

• Deep Inventory: We carry all NH855 piston-related parts in stock, including rare CPL variants.

• Global Shipping: Whether you're working on a marine rebuild in Seattle or an industrial generator in South America, we deliver worldwide.

Applications of the Cummins NH855 Engine

The NH855 engine has been used in a wide variety of heavy-duty platforms. Diesel Pro Power supports NH855 rebuilds in all major sectors:

• Marine Propulsion

• Tugs, trawlers, ferries, and harbor workboats

• Industrial Equipment

• Air compressors, oilfield pump engines, drilling equipment

• Power Generation

• Stationary and mobile generator sets

• Construction

• Wheel loaders, excavators, cranes

• Rail and Locomotive Support

• Track maintenance machinery and auxiliary generators