Narrow Boat Engine Maintenance and Repair

Stephanie L Horton

• Publisher: Crowood
• Year: 2017
• ISBN:
  9781785003509
• Topic: Tecnologia e ingegneria
• Subtopic: Aviazione

When owning a narrow boat, or any engine-powered vessel, it is vital to ensure that the engine is kept in good working order. Narrow Boat Engine Maintenance and Repair is a practical guide to help keep your engine operational, and your boat moving. It also provides instruction on how to identify faults and, where possible, how to fix them. With its focus on diesel engine operation, and the systems found on most vessels, this is a useful resource for any boat owner. It provides practical guidance to undertake everyday maintenance on your diesel engine; it demonstrates how to complete a service and locate and resolve common faults; explains the theory required to understand each of the boat's main systems and shares the practical skills and techniques that engineers spend many years learning. This invaluable resource will be of great interest to those who own and run narrow boats, those starting out and more veteran boat owners. Superbly illustrated with 264 colour step-by-step photographs and 60 technical diagrams.

CHAPTER 1

DIESEL FUEL SYSTEMS

INTRODUCTION

The diesel fuel system is one of the most important systems on a diesel engine and requires more maintenance and upkeep than any other single component or system. It is also the system that is the cause of most breakdowns and can result in expensive repairs when poorly maintained.

Tools required:

• filter wrench
• spanners: 11mm, 13mm, 15mm (selection of others)
• screwdrivers including Phillips
• long-nose pliers or cocktail sticks (for removing seals)
• rags or soak-up mats
• bowl or plastic container.

To assist in understanding and identifying related issues, the diesel system will be broken down into four different systems. These will be referred to as suction fed, low pressure, high pressure and return and are being used for identification of the separate systems only. The fuel system transports fuel from the tank or reservoir through a selection of filters and pumps to deliver clean, pressurized fuel to the engine. However, the type of injection pump will dictate the return system and the components incorporated within it. The diagram shows the three most common arrangements.

Filter wrench for removal of filters.

Basic fuel system with the DPA pump and all the components that make up the fuel system.

Basic fuel system with an inline injection pump – note that there is no return line from the injection pump.

Basic fuel system with a rotary pump – note that the return line goes straight to the tank, not via the filter.

SUCTION-FED FUEL SYSTEM

For our purposes, the suction-fed system covers the components from the tank to the lift pump and includes any pre-filter elements. (It is worth noting that a gravity-fed system would not incorporate a lift pump and would use the head of fuel to gravity-feed the system.) The following section looks at all of the components within this subsystem and describes the type of issues they experience.

Suction-fed system, showing the fuel system from the tank to the lift pump. This system is under a small amount of suction from the lift pump, meaning that there is little or no pressure pushing the fuel through the system.

This system is under a small amount of suction from the lift pump, meaning that there is little or no pressure pushing the fuel through the system. Therefore, this system is susceptible to drawing air in from any leaking unions or pipes, as there is no pressure to force the fuel out and the slight suction from the lift pump contributes to this process. Air pulled into the suction-fed system will eventually lead to air being transported and trapped in the high-pressure system, resulting in an airlock and causing erratic running or the engine to cut out. It is therefore important to ensure that all unions are tight and fuel pipes are sound. (So-called selfbleeding systems will cope with small quantities of air in the system, but will eventually succumb to the issue as it gets worse.)

TIP: IDENTIFYING FUEL PROBLEMS

Fuel leaks usually appear in the suction-fed system when the engine is not operating, because when the engine is running air is drawn into the fuel system and fuel cannot escape. These leaks are usually very small, so can be difficult to locate.

Fuel Tank

The low-pressure system starts at the fuel tank. Its construction and maintenance are important elements of maintaining the fuel system on a boat. Unfortunately, few tanks have all the components shown in the diagram and this can and does result in expensive breakdowns, but aftermarket refits or modifications are not easily implemented. Understanding the impact that tank maintenance can have on the rest of the fuel system is therefore vitally important, and correctly maintaining or managing the fuel in your tank can result in the fuel system running without problems.

Fuel tanks in boats are usually constructed so that the fuel supply pipe for the fuel system is located approximately 25–50mm above the bottom of the tank. The reason for this construction is twofold:

• Most tanks are metal and therefore over time fuel/water/air results in corrosion and rust builds up; this debris drops to the bottom of the tank and remains there.
• The water that is present in the tank, due to condensation and water ingress, naturally separates out and drops to the bottom of the tank when left to stand for periods of time.

In both these cases, the outlet pipe position ensures that neither water nor debris is passed through the fuel system, providing a level of protection from these types of issues.

The boat’s movement can also cause fuel and debris to mix, so baffles are used to prevent the fuel surging about. The tank may have a sloped bottom (or the whole tank may be sloped). This is to ensure that the water and dirt fall to the lowest part, where they can be drained off using the drain tap (if one is fitted). When the tank has not been designed in this way, the debris will sit along the length of the tank floor.

If a drain tap has been fitted, it must also have a cap to comply with the Boat Safety Scheme. The drain cap is there to prevent filling the bilges with diesel should the tap fail, or be inadvertently opened.

Typical example of a marine fuel tank, including all the elements to allow correct maintenance and cleaning and to prevent some of the common issues that are found with some tank designs.

Low-Pressure Pipes

The pipework from the tank to the filters is the start of the suction-fed system. As a general rule, all fuel pipes should be of steel or copper and any joints should be compression fittings. All engines vibrate, no matter how well mounted, so inevitably fuel pipes are subject to the same vibrations. Copper pipes have a tendency to harden over time due to vibration or movement, resulting in them shearing or cracking.

There are a number of arguments that advocate the use of ‘rubber’ flexible hoses, as these naturally dampen vibrations and also start to show signs of wear long before they actually fail. Using flexible hoses running between the engine and hull pipework can offer a number of benefits, as long as the pipe is compliant with BSS standards.

BSS standards recommend that a hose...