Bosch Nozzle Holder Assembly 0431406007 — Wärtsilä 20/28 Marine & Industrial Engine

The Bosch Nozzle Holder Assembly 0431406007 (type formula KB178U906) is a genuine Bosch injection component engineered for the Wärtsilä 20/28 medium-speed diesel engine — one of the most widely deployed marine and industrial prime movers in service today. Carrying Wärtsilä OEM references 009490065, VASA2028, and 167046, this nozzle holder is a direct-fit replacement for the single-cylinder PF pump injection system fitted to all W20/28 cylinder variants. Whether you are an injector specialist carrying out a scheduled overhaul, a marine engineer sourcing spares for a vessel refit, or a fleet operator maintaining a genset installation, part number 0431406007 is the correct Bosch assembly for this application. Stocked as a new (genuine) unit, it is also listed under the successor assemblies 0 431 YK2 458 and 0 432 480 002 in the Bosch large-engine nozzle-and-holder programme. This article covers technical specifications, engine and vessel applications, OEM cross-references, failure symptoms, and frequently asked questions.

Bosch Part Number Reference

Note: Parts 0 431 YK2 458 and 0 432 480 002 are the current Bosch large-engine nozzle-and-holder assembly (LE_NHA) programme equivalents. Verify fitment against your engine serial number and injection system documentation before ordering.

OEM Cross-Reference Numbers

OEM numbers confirmed from engine spare parts documentation, component identification plates, and L20 spare parts catalogue references. Always cross-check against your engine’s official spare parts list (SPL) or Wärtsilä parts portal before ordering.

Injection System Type — Bosch PF Single-Cylinder Pump with Mechanical Nozzle Holder

The Wärtsilä 20/28 uses a Bosch PF single-cylinder injection pump system — one PF pump per cylinder, each paired with a dedicated mechanical nozzle holder assembly. In this arrangement, the PF pump is driven externally by the engine camshaft (the designation “PF” stands for Pumpe mit Fremdantrieb — pump with external drive). The pump element controls injection quantity via a helical control edge, while the nozzle holder assembly determines spray pattern, atomisation quality, and opening pressure.

The nozzle holder assembly itself consists of:

• Nozzle holder body (KB-type) — houses the compression spring, pressure pin, and nozzle retaining nut
• Compression spring — acts on the nozzle needle through the pressure pin to set needle opening pressure
• Pressure pin — transmits spring force to the nozzle needle
• Nozzle — multi-hole type; the needle is lifted by fuel pressure during injection and returns to seat when pressure drops below the spring-set opening pressure

Fuel enters the holder assembly via a high-pressure connection screwed laterally into the nozzle holder. The injection valve is centrally located in the cylinder head, with the high-pressure pipe from the PF pump running inside the protected hot-box enclosure. The Bosch PF + mechanical nozzle holder system supports pressures up to 1,800 bar and is compatible with MDO, HFO, and blended fuels — a critical requirement for the W20/28’s multi-fuel capability.

The KB prefix in type formula KB178U906 designates the Bosch large-engine nozzle holder body series. The numeral group identifies dimensional and pressure characteristics specific to this application.

Engine Application

Engine key data:

• Cylinder bore: 200 mm
• Stroke: 280 mm
• Displacement per cylinder: 8.8 litres
• Number of valves: 2 inlet + 2 exhaust per cylinder
• Mean piston speed: 8.4 m/s (900 rpm) / 9.3 m/s (1,000 rpm)
• Injection system: Bosch PF single-cylinder pump + nozzle holder assembly (one set per cylinder)
• Fuel compatibility: MDO, HFO (up to 700 cSt at 50°C), LFO, biofuel blends
• Introduction: early 1990s; over 7,500 engines delivered

Cylinder Configuration and Power Output Table

Power figures are indicative and vary with speed, rating (continuous/overload), and emission compliance mode. Refer to the engine’s rated output table in the Wärtsilä 20 Product Guide for precise values.

Marine and Industrial Application

The Wärtsilä 20 (engine code 20/28 — 200 mm bore × 280 mm stroke) is a versatile medium-speed diesel platform used across a wide range of marine vessel types and land-based power generation installations. Typical marine applications include:

• Merchant vessels — container feeders, bulk carriers, RoRo ferries, product tankers
• Offshore support vessels (OSV), platform supply vessels (PSV)
• Dredgers and crane vessels
• Naval patrol and auxiliary vessels
• Cruise ships and large passenger ferries (auxiliary generating sets)
• Pure car and truck carriers (PCTC)

In land-based applications, the W20 is used in distributed power plants and industrial gensets, particularly where compact footprint and fuel flexibility are required. Since its introduction in the early 1990s, more than 7,500 Wärtsilä 20 engines have been delivered worldwide, making spare part availability and service expertise well-established in the market.

Technical Specifications

Common Failure Symptoms

A worn or damaged nozzle holder assembly on the Wärtsilä 20/28 engine will produce one or more of the following symptoms. Prompt replacement of the affected unit prevents progressive combustion damage and emission non-compliance.

• Smoky exhaust (black or blue smoke) — a leaking or dribbling nozzle causes incomplete combustion and unburnt fuel particles in the exhaust gas
• Hard starting or misfiring on individual cylinders — an injector failing to open correctly at the set pressure disrupts cylinder firing, causing rough running or persistent misfire
• Reduced power output and increased fuel consumption — poor atomisation reduces combustion efficiency; the fuel management system may compensate with higher delivery rates, increasing consumption
• Engine knock or irregular combustion noise — delayed or erratic injection due to a stuck or worn nozzle needle causes audible knock, particularly noticeable at low load
• Elevated exhaust gas temperature (EGT) on one cylinder — a nozzle that dribbles after injection causes prolonged combustion and a measurable spike in individual cylinder EGT on the monitoring system
• Fouled nozzle tip or carbon build-up — nozzle holes blocked by carbon deposits reduce spray cone quality and injection quantity, identified during nozzle testing or visual inspection at scheduled overhaul
• Fuel dilution of lubricating oil — in severe cases, a cracked nozzle holder body or failed sealing surfaces allows fuel to migrate into the crankcase, reducing lube oil viscosity and increasing wear risk
• Failed nozzle test (opening pressure out of specification) — at scheduled service intervals, nozzle holders are bench-tested; a spring that has lost pre-load or a worn needle seat will fail to meet the specified opening pressure

Frequently Asked Questions

1. What does part number 0431406007 replace, and is there a current successor part?

Bosch part 0431406007 (type KB178U906) is the nozzle holder assembly for the Wärtsilä 20/28 engine as listed in the original injection system documentation. Bosch’s current large-engine nozzle-and-holder assembly programme lists 0 431 YK2 458 and 0 432 480 002 (both designated LE_NHA) as the programme equivalents. If 0431406007 is offered as new-old-stock or a service replacement under this number, it is functionally correct for the application. Always verify against your Wärtsilä spare parts list (SPL) and engine serial number before ordering.

2. What are the Wärtsilä OEM part numbers for this nozzle holder?

The confirmed Wärtsilä OEM cross-references for Bosch 0431406007 are 009490065 (primary Wärtsilä spare parts catalogue number) and VASA2028 (the historic VASA programme reference used in earlier documentation and identification plates). Both numbers refer to the same nozzle holder assembly as fitted to the W20/28 cylinder configuration.

3. How many nozzle holder assemblies does a Wärtsilä 20 engine require?

The Wärtsilä 20 uses one nozzle holder assembly per cylinder, paired with one Bosch PF injection pump per cylinder. A 6L20 therefore requires six units, an 8L20 requires eight, and a 9L20 requires nine. When carrying out a full fuel system overhaul it is standard practice to replace or recondition all holders simultaneously to ensure balanced cylinder performance.

4. Can this nozzle holder operate on heavy fuel oil (HFO)?

Yes. The Wärtsilä 20 is designed for continuous operation on HFO with a maximum viscosity of 700 cSt at 50°C. The Bosch PF single-cylinder pump and mechanical nozzle holder assembly used on this engine are specifically designed for robust multi-fuel operation, including HFO, blended fuels, MDO, and LFO. The through-flow design of the PF pump and the robust construction of the KB-series nozzle holder support sustained heavy fuel running without requiring changeover to distillate at low load — provided the fuel is correctly pre-heated and conditioned to the appropriate injection viscosity.

5. What is the correct overhaul and replacement interval for this nozzle holder on the Wärtsilä 20?

Wärtsilä publishes overhaul intervals in the W20 Product Manual, and these vary depending on operating conditions, fuel quality, and engine load profile. As a general guide, nozzle holders on medium-speed engines operating on HFO are typically inspected and bench-tested at each major periodic overhaul — commonly every 8,000–12,000 running hours — with replacement carried out when opening pressure is out of specification, needle wear is confirmed, or spray pattern fails nozzle testing. Always refer to the engine-specific maintenance schedule supplied with your unit.

6. What is the difference between a nozzle holder assembly and a nozzle-and-holder assembly (LE_NHA)?

A nozzle holder assembly (such as 0431406007) consists of the holder body, compression spring, pressure pin, and retaining nut — but the nozzle (needle and nozzle body) is a separate serviceable component and is ordered and replaced independently. A nozzle-and-holder assembly (LE_NHA) — as designated on successor parts 0 431 YK2 458 and 0 432 480 002 — is a complete pre-assembled unit including both the holder and the nozzle. The LE_NHA format simplifies overhaul logistics and ensures the nozzle and holder are always matched as a new pair. When ordering, confirm with your parts supplier whether the holder-only or the complete nozzle-and-holder assembly is required for your overhaul scope.

7. What fuel types are compatible with this injection system?

The Bosch PF + KB-series nozzle holder system on the Wärtsilä 20 is compatible with the full range of fuels the engine is rated for: marine diesel oil (MDO), light fuel oil (LFO), heavy fuel oil (HFO), ultra-low sulphur fuel (ULSFO), and crude liquid biofuels or biodiesels meeting Wärtsilä’s fuel specification tables. Operation on blended fuels with a viscosity of approximately 4–7 cSt at 100°C (roughly 12–30 cSt at 50°C) — representing 30–60% distillate blends — should be avoided due to the risk of asphaltene precipitation in the blend. Consult the Wärtsilä 20 Product Manual Chapter 2 (Fuel) for complete fuel specification guidance.

8. Is genuine Bosch or OEM quality important for this application?

For medium-speed marine engines operating on HFO in continuous-duty service, genuine Bosch or verified OEM-quality nozzle holder assemblies are strongly recommended. The nozzle holder spring pre-load, needle seat geometry, and surface finish tolerances directly determine opening pressure accuracy, spray atomisation quality, and combustion efficiency. Substandard aftermarket components can result in opening pressure drift, premature needle seat wear, combustion anomalies, and — in worst cases — nozzle seizure. For classification-surveyed vessels and power plant installations, traceability to genuine Bosch part numbers also supports compliance documentation.

Conclusion

Bosch Nozzle Holder Assembly 0431406007 (type formula KB178U906) is the correct OEM-grade injection component for the Wärtsilä 20/28 medium-speed diesel engine across all cylinder configurations (4L, 6L, 8L, 9L) built from 1993 onwards. With Wärtsilä OEM references 009490065 and VASA2028, and successor assemblies available under the LE_NHA programme (0 431 YK2 458 / 0 432 480 002), this part is well-supported across the global Wärtsilä service network. Whether you are overhauling a single cylinder or completing a full engine service, sourcing genuine Bosch components is the lowest-risk approach for a platform that may be running 8,000-plus hours per year in demanding marine or industrial conditions.

To order Bosch 0431406007 or to discuss availability and lead times, visit our product page or contact our technical sales team directly. We stock genuine Bosch large-engine injection components and can advise on complete overhaul kits for the Wärtsilä 20 platform.