The lubrication system of an internal-combustion engine is very important. If the lubricating system should fail, not only will the engine stop, but many of the parts are likely to be damaged beyond repair. Therefore, when lubrication failure occurs, the engine can seldom be run again without a major overhaul.

The lubricating system delivers oil to the moving parts of the engine to reduce friction and to assist in keeping the parts cool. Most diesel and gasoline engines are equipped with a pressure lubricating system that delivers the oil under pressure to the bearings and bushings and also lubricates the gears and cylinder walls. The oil usually reaches the bearings through passages drilled in the framework of the engine. The lubricating system of a typical diesel engine is shown in figure 7-10

All of the engine parts are lubricated with oil delivered by a gear-type oil pump. This pump takes suction through a screen from an oil pan or sump. From the pump, the oil is forced through the oil filter and the oil cooler into the main oil gallery. The oil is fed from the main gallery, through individual passages, to the main crankshaft bearings and one end of the hollow camshaft. All the other moving parts and bearings are lubricated by oil drawn from these two sources. The cylinder walls and the teeth of many of the gears are lubricated by oil spray thrown off by the rotating crankshaft. After the oil has served its purpose, it drains back to the sump to be used again.

The oil pressure in the line leading from the pump to the engine is indicated on a pressure gauge. A temperature gauge in the return line provides an indirect method for indicating variations in the temperature of the engine parts. Any abnormal drop in pressure or rise in temperature should be investigated at once. It is advisable to secure (shut down) the engine until the trouble has been located and corrected.

Constant oil pressure, throughout a wide range of engine speeds, is maintained by the oil pressure relief valve that allows the excess oil to flow back into the sump. All of the oil from the pump passes through the filter unless the oil is cold and heavy or if the filter (or oil cooler) is clogged. In such cases, the bypass valve (filter bypass valve or cooler bypass valve) is forced open; and the oil flows directly to the engine. Part of the oil fed to the engine is returned through the bypass filter, which removes flakes of metal, carbon particles, and other impurities.

COOLING SYSTEM

Marine engines are equipped with a watercooling system to carry away the excess heat produced in the engine cylinders. Fresh water (coolant) is circulated through passages in the cylinder walls and in the cylinder head, where it becomes hot from absorbing engine heat. The hot coolant then passes through a heat exchanger, where it gives up its heat to a cooling medium, becomes cool, and returns to the engine to remove more heat. The cooling medium may be either air or seawater.

A heat exchanger using air as the cooling medium works like an automobile radiator. A heat exchanger using seawater as the cooling medium may be mounted either on the engine or on the ship's hull. Engine-mounted heat exchangers require seawater to be pumped to and from them; whereas, hull-mounted heat exchangers (keel coolers) are in constant contact with seawater and require the fresh water (coolant) to be pumped through the cooler.

STARTING SYSTEMS

There are three types of starting systems used in internal-combustion engines-electric, hydraulic, and compressed air.

As a Fireman, you will probably have more contact with the electric starting system than you will with the other two types. Lifeboats aboard ships use an electric starter to start the engine.

Electric starting systems use direct current because electrical energy in this form can be stored in batteries and drawn upon when needed. The battery's electrical energy can be restored by

Figure 7-11.-Electric starting system.

charging the battery with an engine-driven generator.

The main components of the electric starting system, as shown in figure 7-11 are the battery, cranking motor, and associated control and protective devices.

Electric Starting Systems

The starting motor for diesel and gasoline engines operates on the same principle as a direct current electric motor. The motor is designed to carry extremely heavy loads but, because it draws a high current (300 to 665 amperes), it tends to overheat quickly. To avoid overheating, NEVER allow the motor to run more than the specified amount of time, usually 30 seconds at a time. Then allow it to cool for 2 or 3 minutes before using it again.

To start a diesel engine, you must turn it over rapidly to obtain sufficient heat to ignite the fuel. The starting motor is located near the flywheel, and the drive gear on the starter is arranged so that it can mesh with the teeth on the flywheel when the starting switch is closed. The drive mechanism must function to (1) transmit the turning power to the engine when the starting motor runs, (2) disconnect the starting motor from the engine immediately after the engine has started, and (3) provide a gear reduction ratio between the starting motor and the engine.

The drive mechanism must disengage the pinion from the flywheel immediately after the engine starts. After the engine starts, its speed may increase rapidly to approximately 1,500 rpm. If the drive pinion remained meshed with the flywheel and also locked with the shaft of the starting motor at a normal engine speed

(1,500 rpm), the shaft would be spun at a rapid rate (22,500 to 30,000 rpm). At such speeds, the starting motor would be badly damaged.

Hydraulic Starting Systems

There are several types of hydraulic starting systems in use. In most installations, the system consists of a hydraulic starting motor, a pistontype accumulator, a manually operated hydraulic pump, an engine-driven hydraulic pump, and a reservoir for the hydraulic fluid.

Hydraulic pressure is provided in the accumulator by the manually operated hand pump or from the engine-driven pump when the engine is operating.

When the starting lever is operated, the control valve allows hydraulic oil (under pressure of nitrogen gas) from the accumulator to pass through the hydraulic starting motor, thereby cranking the engine. When the starting lever is released, spring action disengages the starting pinion and closes the control valve. This stops the flow of hydraulic oil from the accumulator. The starter is protected from the high speeds of the engine by the action of an overrunning clutch.

The hydraulic starting system is used on some smaller diesel engines. This system can be applied to most engines now in service without modification.

Air Starting Systems

Starting air comes directly from the ship's medium-pressure (MP) or high-pressure (HP) air service line or from the starting air flasks which are included in some systems for the purpose of storing starting air. From either source, the air, on its way to the starting air system, must bypass through a pressure-reducing valve, which reduces the higher pressure to the operating pressure required to start a particular engine.

A relief valve is installed in the line between the reducing valve and the starting system. The relief valve is normally set to open at 12 percent above the required starting air pressure. If the air pressure leaving the reducing valve is too high, the relief valve will protect the system by releasing air in excess of a preset value and permit air only at safe pressure to reach the starting system of the engine.

START AIR MOTOR SYSTEM.- Some engines, usually gas turbine types, are designed to crank over by starting motors that use compressed air. Air-starting motors are usually driven by air pressures varying from 90 to 200 psi.

COMPRESSED AIR ADMISSION SYSTEM.Most large diesel engines are started when compressed air is admitted directly into the engine cylinders. Compressed air at approximately 200 to 300 psi is directed into the cylinders to force the piston down and thereby, turn the crankshaft of the engine. This air admission process continues until the pistons are able to build up sufficient heat from compression to cause combustion to start the engine.