Mastering Your Bukh DV20 Marine Diesel Engine

For generations of boaters across the UK and beyond, the name Bukh has been synonymous with robust, reliable marine diesel engines. Among their revered lineup, the Bukh DV10 and its two-cylinder sibling, the DV20, stand out as true workhorses, meticulously engineered to meet the demanding conditions of marine environments. These engines, proudly Danish in origin, were designed from the outset with stability, safety, and environmental considerations at their core, earning them a reputation for longevity and dependable performance. Understanding the intricate details of your Bukh DV20 is key to ensuring its continued smooth operation and extending its already impressive lifespan, whether you're embarking on a short coastal hop or a more ambitious voyage.

The Heart of Your Vessel: Understanding the Bukh DV10 & DV20 Engines

At their essence, the Bukh DV10 and DV20 are water-cooled, 4-stroke marine diesel engines, distinguished by their innovative pre-combustion chamber principle with 2-stage combustion. While the DV10 operates with a single cylinder, the DV20 doubles the power with two cylinders, built upon the same foundational design philosophy. The DV10 itself was available in various configurations, including the DV10 M (manual start only), DV10 ME (manual and electric start), and the DV10 SME (a Saildrive version). This modular approach speaks to Bukh's commitment to versatility and adaptability, principles that extend to the DV20, ensuring it too is a formidable power unit for a wide array of marine applications.

These engines are not merely assemblies of parts; they are integrated systems, each component meticulously designed and crafted to perform under pressure. Their resilience stems from the high-quality materials and precision engineering employed throughout their construction, a testament to Bukh's dedication to marine excellence.

Engineering Excellence: A Closer Look at Key Components

The reliability of the Bukh DV20 is rooted in the quality and design of its individual components. A deeper dive into these parts reveals the thoughtful engineering that contributes to the engine's legendary durability.

Cylinder Head

The cylinder head, a critical component, is fabricated from a highly alloyed special cast iron, chosen specifically for its exceptional resistance to both thermic and mechanical loads. Each cylinder unit within the DV20 is equipped with dedicated exhaust and suction valves. The generously sized suction valve, coupled with aerodynamically designed exhaust and suction manifolds, ensures optimal flushing of the cylinders, which is vital for efficient combustion and engine longevity. Both valves operate within replaceable valve guides, made from a special cast iron for superior wear qualities. The valve seats, shrink-fitted into the cylinder head, are crafted from heat-resisting special steel, providing high mechanical wearing quality. Similarly, the valves themselves are made from special steel, prized for their high strength, toughness, and excellent heat resistance, all contributing to the engine's reliable performance even under strenuous conditions.

Crankcase

The engine's crankcase, the robust backbone of the DV20, is constructed from special cast iron. It features strong, strategically placed ribs that impart immense toughness and strength to the structure. The unique tunnel-shaped bore for the crankshaft further enhances this rigidity, creating a foundation that can withstand the significant forces generated during engine operation, ensuring long-term structural integrity.

Crankshaft

Crafted from die-forged chrome steel, the crankshaft is the heart of the engine's motion. Each crank throw is fitted with special counterweights, meticulously balanced to ensure incredibly smooth running of the engine, minimising vibrations and enhancing comfort aboard. Unlike the DV10 which uses two main bearings, the DV20, being a two-cylinder engine, not only utilises two main bearings but also incorporates an intermediate bearing for enhanced stability and support. These bearings are made from steel with a tin aluminium alloy, a material chosen for its ability to withstand high pressures without degradation. Axial direction of the crankshaft is precisely controlled by turned surfaces on the crank throws and contact faces on the end cover and the intermediate bearing, ensuring proper alignment. The engine's sealing is maintained by oil seal rings fitted in the end covers, preventing lubricant leaks and maintaining system integrity.

Flywheel

The large-dimensioned flywheel, made from cast iron, is bolted securely onto the crankshaft at the engine's front end. Its substantial size is crucial for securing steady operation of the engine, dampening power fluctuations and ensuring a smooth power delivery. The flywheel features a V-belt groove, which serves to drive the engine's electrical equipment, such as the alternator, and the cooling water circulating pump. Furthermore, the flywheel can be adapted with an extra three-groove V-belt pulley or a flat belt pulley, offering versatility for additional accessory drives.

Connecting Rod

Each connecting rod is a die-forged component with an H-shaped section, a design known for its optimal strength-to-weight ratio. The bearing cap is an integral part of the connecting rod itself, designed for maximum integrity. The base of the bearing is individually adapted for each connecting rod and guided precisely by two steel balls. The connecting rod bearings themselves consist of steel shells with a tin aluminium alloy, securely fastened in the bearing cap and base with two Allen steel bolts. The bearing for the piston pin is a special bronze bushing, chosen for its durability and low friction properties, facilitating smooth piston movement.

Piston and Cylinder Liner

The pistons are made from a light alloy, a choice that balances strength with reduced reciprocating mass, contributing to smoother engine operation. The combustion chamber is ingeniously shaped directly within the piston head, optimising the combustion process. Each piston is fitted with three compressing rings and a single oil scraper ring, essential for maintaining compression and controlling oil consumption. The piston pin, which is hollow and made from hardened steel, floats within its bore and is locked in axial direction by circlips, ensuring secure yet flexible movement.

The cylinder liner, an internal sleeve within the crankcase, is made from spun cast iron with a high carbon content. This material choice provides exceptional wearing qualities, crucial for the long life of the engine. The cylinder liner is precisely guided within the crankcase by a recess at the top and a conical bore at the bottom. Tightening and sealing are achieved through a specially made cylinder-head gasket and two O-rings in the conical bore, preventing leaks and maintaining optimal compression.

Camshaft

For maximum strength and rigidity, the camshaft and its associated cams, which activate the suction and exhaust valves, are cast in one piece. The cams themselves are case-hardened, enhancing their stability and resistance to wear, which is vital given their constant interaction with the valve train. The camshaft is driven by a gear-wheel on the crankshaft and a shrink-fitted gear-wheel on the camshaft itself. These gear-wheels are meticulously marked in proportion to each other, and it is absolutely critical that these markings are observed with the greatest accuracy during any removal or reassembly processes to ensure correct engine timing. Additionally, a fuel pump cam is fitted to the camshaft, designed to alter the injection time in accordance with engine revolutions, optimising fuel delivery across the RPM range.

Essential Systems for Operation

Beyond the core mechanical components, several vital systems work in harmony to ensure the Bukh DV20 operates efficiently and reliably.

Lubricating Oil System

The Bukh DV20 employs a pressure lubrication system, powered by a high-efficiency rotary type lubricating oil pump (often an Eaton pump). This pump is driven by the camshaft and is typically located on the engine's rear end cover. The lubricating oil pressure is precisely controlled by a spring-loaded pressure relief valve, ensuring that all moving parts receive adequate lubrication without excessive pressure, which protects seals and components from undue stress.

Cooling Water System

Maintaining the correct operating temperature is paramount for engine efficiency and longevity. The DV20's cooling-water temperature is thermostat-controlled, providing a constant and effective operating temperature regardless of ambient conditions or engine load. Bukh DV20 engines can be delivered with either direct or indirect cooling systems, offering flexibility depending on the vessel's specific setup and the owner's preference.

Fuel System

The fuel system is designed for precise and efficient fuel delivery. Fuel is supplied to the engine from the fuel valve, which is strategically placed in the cylinder head. This valve receives fuel under high pressure from the fuel pumps, which are activated directly from the camshaft. Before reaching the fuel pumps, fuel is drawn from the main fuel tank via a lift pump and passes through an effective filter, ensuring that only clean fuel reaches the sensitive injection components, preventing blockages and wear.

Starting Your Bukh DV20: The Electric Starter Motor

Modern convenience for Bukh DV engines arrived in 1974 when the gear rim starter superseded the older dynastarter in both the DV10 and DV20 models. For the DV10 engine, units with serial number #89157 and up were equipped with the gear rim starter. Similarly, for the DV20 model, engines with serial number #93638 and up featured this improved starting mechanism. It's important to note that the starter gear is typically disengaged when the motor is running or stopped. When power is applied to the starter motor, a Bendix gear mechanism forces a small pinion gear to engage with the gearing on the flywheel, initiating engine rotation. If you find your starter motor spinning but the flywheel isn't turning, this often indicates a problem with the Bendix gear, which may be failing to engage properly.

Understanding Your Engine: Specifications and Comparisons

While specific power output and weight figures for the DV20 were not explicitly detailed in the provided information, we can infer much about its characteristics by comparing it to its single-cylinder counterpart, the DV10, which shares much of the same design philosophy and componentry.

Bukh DV10 Specifications (for context):

Given that the DV20 is a two-cylinder engine, it would inherently have double the volume of the DV10's 0.482 litres, meaning approximately 0.964 litres. This increased displacement, combined with the additional cylinder, would naturally lead to a significantly higher power output and, consequently, a greater dry weight than the DV10 models. The design principles for components like pistons, connecting rods, and lubrication systems remain consistent, but the DV20 incorporates an intermediate bearing on its crankshaft, a feature not found on the single-cylinder DV10, providing extra support for the longer, two-throw crankshaft.

Component Overview (Port & Starboard Sides - General to DV Series)

Understanding the location of key components can aid in routine checks and troubleshooting:

Port Side Components (Common Examples):

• Cooling water pump
• Oil dipstick
• Water drain from engine block
• Fuel lift pump with manual priming
• Fuel filter
• Exhaust pipe
• Regulating lever (and bracket for remote control)
• Fuel pump
• Electro-magnetic stop-coil
• Lubricating oil pump
• Bracket for remote control of reversing gear
• Reverse-reduction gear
• Coupling flange for propeller shaft
• Oil dipstick for reverse-reduction gear
• Reversible engine mountings

Starboard Side Components (Common Examples):

• Gear lever for reverse-reduction gear
• Lubricating oil filter
• Oil pressure switch
• Oil sump
• Decompression lever
• Oil filling plug
• Cooling water thermostat
• Zinc rod
• Nozzle holder
• Air cleaner with silencer
• Raised hand start (if applicable)
• Alternator
• Starter
• Electric multi-plugs

Familiarity with these locations is invaluable for routine maintenance and quick diagnostics.

Maintenance and Troubleshooting: Keeping Your DV20 Running Smoothly

The longevity of a Bukh DV20 engine is not just a testament to its initial build quality, but also to consistent and diligent maintenance. Regular checks and prompt attention to minor issues can prevent major problems down the line.

• Consult Your Manual: The most important tool in your maintenance arsenal is the engine's Workshop Manual. As noted, manuals are indeed available for the Bukh DV20 Marine Diesel Engine, including a comprehensive Workshop Manual available for free PDF download. This document is your definitive guide to service intervals, torque settings, and troubleshooting procedures.
• Routine Checks: Regularly inspect oil levels, coolant levels, and the condition of fuel filters. Look for any signs of leaks, unusual wear, or corrosion.
• Listen to Your Engine: Pay attention to any changes in engine sound, vibration, or performance. Often, subtle changes can be early indicators of developing issues.
• Fuel Quality: Always ensure you are using clean, high-quality diesel fuel and that your fuel filters are regularly inspected and replaced as per the manual's recommendations.
• Cooling System: Monitor your engine's temperature gauge. Ensure the raw water intake is clear and that your thermostat is functioning correctly to maintain optimal operating temperature.
• Starter System: If you experience starting issues, particularly if the starter motor spins but the engine doesn't turn over, investigate the Bendix gear as a likely culprit.

Frequently Asked Questions About the Bukh DV20

Here are some common questions boat owners have regarding the Bukh DV20 marine diesel engine:

Are user manuals available for the Bukh DV20 marine diesel engine?

Yes, user manuals and guides are available for the Bukh DV20. Specifically, a Workshop Manual is known to be available for free PDF download, which is an invaluable resource for maintenance and repairs.

What are the fundamental differences between the Bukh DV10 and DV20 engines?

The primary difference is the number of cylinders: the DV10 is a single-cylinder engine, while the DV20 is a two-cylinder engine. Both share the same fundamental 4-stroke, water-cooled, pre-combustion chamber design. The DV20 also features an additional intermediate bearing on its crankshaft for enhanced support, which the single-cylinder DV10 does not require.

How can I tell if my Bukh DV20 has an electric starter motor?

If your DV20 engine has a serial number of #93638 or higher, it should be equipped with the gear rim electric starter motor. Earlier models may have had a dynastarter, which was phased out in 1974.

What should I do if my starter motor spins but doesn't engage the engine?

If you hear the starter motor spinning but the engine's flywheel isn't turning, it's highly likely that the Bendix gear is faulty or stuck. This component is responsible for extending the starter's pinion gear to mesh with the flywheel's ring gear. Inspection and possible replacement of the Bendix mechanism would be the next step.

What type of cooling system does the Bukh DV20 use?

The Bukh DV20 engines can be delivered with either a direct or indirect cooling system. Both systems are thermostat-controlled to ensure a consistent and effective operating temperature for the engine, optimising its performance and longevity.

Is the Bukh DV20 engine heavy?

While a specific dry weight for the DV20 was not provided, as a two-cylinder marine diesel engine, it would naturally be heavier than its single-cylinder DV10 counterpart (which ranges from 140 kg to 160 kg dry weight depending on configuration). Its robust construction and marine-grade components contribute to its substantial, durable build.

Conclusion

The Bukh DV20 marine diesel engine is a testament to enduring Danish engineering, offering boat owners a powerful, reliable, and meticulously designed heart for their vessels. Its robust construction, featuring high-quality components like the special cast iron cylinder head and the spun cast iron cylinder liner, ensures exceptional durability. Understanding its core systems – lubrication, cooling, and fuel – and familiarising yourself with key components, empowers you to perform effective maintenance and troubleshoot common issues. With the availability of a comprehensive Workshop Manual and a proactive approach to care, your Bukh DV20 can continue to deliver dependable performance for many years, keeping you confidently on the water, wherever your nautical adventures take you.

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