Tuesday, July 16, 2013

Marine Engine Series Part 3: Operating a Marine Engine

Operating a Marine Engine
6.1 Starting Methods

There are four different methods for starting marine diesel engines.

·      Hand start, Battery operated starter motor, Hydraulic start & Air start
Hand start
Hand starting is usually fitted to smaller engines although some manufacturers do provide them on larger engines.

On the smaller engines, a starting handle engages in the end of the crankshaft.

The starting handle should be held with all fingers and the thumb on one side of the handle. If the thumb is placed on the opposite side to the fingers, and the engine back fires, the thumb could be broken.

The starting handle is turned until the engine has sufficient cranking speed for it to fire.

The compression pressure of a diesel engine is higher than that of a petrol engine, therefore more effort is required. To make the engine easier to turn, decompression levers may be fitted to relieve the pressure in one or a number of cylinders, not necessarily all cylinders.

A decompression device is a mechanism that is actuated by a lever, which holds the inlet or exhaust valve off its seat. This means that when the piston ascends on its compression stroke, no compression or resistance is there because the air is flowing straight out the inlet or exhaust valve (whichever one is decompressed).

The decompression lever/s are conveniently placed to the starting handle so one person can operate both:

1.         The decompression lever/s are engaged

2.         The engine is hand cranked until it attains sufficient cranking speed

3.         The decompression lever/s are released allowing full compression pressure and

4.         The engine fires.




On the larger engines, the starting handle is operated by sprockets and a chain with a ratio to provide easier turning. The decompression levers are operated by a second person. This means of starting on the larger engines is an additional emergency method. The main means is an electric starter motor.

Battery operated starter motor
The battery operated starter motor is now commonly used on large engines of high kW power.

Due to the high compression pressures mentioned previously, starter motors draw a very high current for a short period of time. The connections on the batteries and starter motor must be clean and tight. The starting motor leads must be kept as short as possible to prevent voltage drop and the wire size must be sufficient to take the high current.

A solenoid on the starter motor is energised and causes a pinion to engage with the ring gear on the flywheel. The starter motor turns the pinion until the engine attains sufficient cranking speed to fire. On firing, centrifugal force of the pinion causes it to disengage from the ring gear.

Variations include starter motors which employ a clutch. Others have reduction gearing to enable the starter motor to rotate at high speed with comparatively low torque which is multiplied by the gear ratio.  

Hydraulic starting system





A hydraulic starting system is normally used on a stationary engine that drives an emergency pump, or an engine on a vessel that needs to be started first to get all machinery running.

The hydraulic starting system consists of:

·      an oil reservoir
·      a hand pump
·      an accumulator
·      a pressure gauge
·      a hydraulic driven starter motor plus
·      connecting hoses and fittings

Operation
Hydraulic oil from the oil reservoir is pumped by the hand pump into the accumulator.

The accumulator is divided by a synthetic diaphragm which is filled with compressed air of around 1,400 kPa (200 psi). The diaphragm is sealed to stop the air leaking out.

The oil is pumped into the lower portion of the accumulator and increases the pressure of the air. A manually operated control valve on the bottom of the accumulator allows the oil to flow to the starter motor which rapidly accelerates the engine to a high cranking speed. The fluid returns directly to the reservoir from the starter motor.

Starting Procedure

Step
1
Ensure oil in the reservoir is at the correct level.
2
Use the hand pump to raise the pressure in the accumulator to provide adequate cranking speed to start the engine.
3
Set throttle to the start position.
4
Push the control valve lever on the accumulator to allow the pressurised oil to flow to the starter motor.
5
Close the control valve quickly when the engine starts to conserve the accumulator pressure and to prevent excessive overrunning of the starter drive clutch assembly.





Detroit Diesel have a hydraulic starting system called a hydrostarter. It is basically the same as above, but uses nitrogen in the accumulator instead of compressed air. In addition, it has a engine driven pump so the system is automatically recharged after each start. It still has a hand pump so it can also be manually recharged.

There are also different types of hydraulic starter motors.

Air start method


There are a number of variations, but only the distributor type will be explained.

The principle is to allow compressed air into the cylinder to push the piston down and rotate the engine fast enough so that it fires on the fuel.

The air must be fed into the cylinder when that cylinder is on the power stroke and about 10 to 15 degrees past top dead centre. On the power stroke, both inlet and exhaust valves are closed, so the compressed air cannot escape when it is fed into the cylinder.




The air is fed into the cylinder via an air start valve situated in the cylinder head. There is normally one air start valve for each cylinder. On some V12 and V16 engines, air start valves are only fitted to one bank of cylinders to save on costs.

The air start valve is a spring loaded valve. It opens when compressed air is fed to it and will close when the air is shut off to it.

The air is supplied to each air start valve via an air distributor. The distributor is mounted on the end of the camshaft. It has a steel disc. A hole is drilled through the disc and as it rotates, it lines up with holes in the distributor body, the number of which are equal to the number of cylinders. Pipes are connected from these holes in the distributor body, in the firing order sequence, to each air start valve.

The air is stored in and supplied from an air receiver. A multi stage compressor is required to supply the air to the receiver. The compressor is usually connected to a diesel engine that is hand started, or by a battery operated starter motor.

Starting procedure

Step
1
Ensure the air receiver (bottle) is fully charged with compressed air.
2
Drain off any water and oil in the air receiver.
3
Check the indicator cocks are open and bar the engine over at least one complete revolution to ensure there is no fresh water in a cylinder. Close the indicator cocks.
4
Open the stop valve on the air receiver.
5
Place the fuel lever in the start position.
6
Place the air starting lever in the start position.
Air will now flow to the cylinder that has just started its power stroke. The pressure of the air will open the air start valve and air entering the cylinder will force the piston down.
7
The rotation of the engine will cause the distributor to shut off air to that cylinder and supply air to the next cylinder in the firing order.
8
When the engine fires, release the air starting lever. (It is usually spring loaded).
9
Shut the stop valve on the air receiver.
10
Recharge the air receiver.



6.2 Precautions with air start engines

Where the propulsion engine is fitted with a gear box, the air receiver stop valve must be closed whilst the engine is running.

The air start valves must be checked to ensure they are seating. This can be checked by placing a hand on the air pipe at each air start valve. If the valve is leaking, the hot gases of combustion will pass the valve seat and flow into the air supply pipe. A bad leak will cause the air supply pipe to glow red.

Should the air compressor be pumping oil, this oil will finish up in the air receiver and an explosion could occur.

A non-return valve is fitted in the air line between the air receiver stop valve and the distributor. This is to prevent the hot gases going back into the air receiver and possibly causing an explosion.

An air receiver is a pressure vessel and should be treated with respect. It is essential to drain any water out of it regularly to prevent internal corrosion. At the same time, oil would be drained from it, sometimes in the emulsified form, to prevent explosions. Should the oil be excessive, the air compressor should be overhauled. Survey requires the air receiver to be inspected internally and the relief valve set annually. The relief valve must be set and floated in the presence of the surveyor. A safety valve should never be altered or interfered with.

6.3 Engine protection devices

Survey requirements are that a propulsion engine shall be provided with an audible warning device to indicate a dangerous condition associated with:

(a)       engine lubricating oil pressure

(b)       engine jacket cooling water outlet temperature and

(c)        engine gear box lubricating oil pressure.

As noted, these protection devices give off an audible warning only. Automatically shutting down a propulsion engine without any warning could result in collision, grounding, or the loss of the vessel. Crossing a bar entrance is an example.




The alarm system may have an alarm switch that must be turned on manually to put the system into operation. The danger of this system is the operator may forget to activate the system. The engine will then run in an unprotected mode. It is preferable that there be no alarm switch.

If there is an alarm switch, it is good practice to switch it on before starting the engine. It will sound until the engine is started and the minimum oil pressure registers. Similarly, it should not be switched off until the engine is stopped and the alarm sounds. This procedure checks that the pressure components of the alarm are operational.

The gear box low lubricating oil pressure alarm operates in the same fashion as the engine low oil pressure alarm.

Low oil pressure alarm
The oil pressure alarm consists of a pressure switch fitted to the pressure side of the lubricating oil system, usually into an oil gallery. The oil pressure acts on a diaphragm and spring which open the contacts in a micro switch. When the spring pressure is greater than the oil pressure, the contacts will close and sound the audible alarm. 

If an alarm switch is fitted, switch it on. When the engine is started, the oil pressure switch opens as the oil pressure reaches approximately 69 kPa (10 psi) and the alarm will cease to sound.

Likewise, if the oil pressure drops below the setting of 69 kPa (10 psi), the oil pressure switch will close the circuit and sound the audible alarm.

The alarm will continue to sound until the engine is stopped or if an alarm switch is fitted, it is switched off.

High temperature fresh water alarm
The high temperature fresh water alarm consists of a thermo switch. It has a bi-metal probe that activates contacts in a micro switch. It is installed in the side of the thermostat housing.

When the engine is started and running at normal operating temperature, the contacts in the switch will be open. Should the engine coolant exceed say 96°  3° C (205°  5° F) the water temperature switch will close the electrical circuit and sound the audible alarm.

The alarm will continue to sound until the temperature drops below the above mentioned setting.




A Detroit Diesel engine has an additional sensor fitted for the protection of their engines. It will also sound the alarm on a large loss of coolant. A big and sudden loss in coolant may reduce the coolant level to below the probe in the thermostat housing. As the water is not now circulating over this probe, it will not detect the rise in temperature of the coolant. An additional sensor is fitted into the exhaust manifold outlet to detect the rise in temperature due to overheating.

The water temperature switch consists of a temperature-sensing valve and a micro-switch. The valve contacts a copper plug (heat probe) which extends into the exhaust manifold outlet. Engine coolant is directed over the power element of the valve. Should the water temperature exceed its setting, the valve will close the contacts in the micro-switch. This closes the circuit and sounds the audible alarm. If a loss of coolant occurs, the heat of the exhaust gases will be transmitted through the copper plug to the temperature-sensing valve, closing the circuit and sounding the audible alarm.

Emergency stop device
Numerous diesel engines are fitted with a manually operated emergency engine shut down device. This is mounted in the air inlet housing, to stop the engine if an abnormal condition should arise. If the engine continues to run after the engine throttle is placed in the “no fuel” position, or if combustible liquids or gases are accidentally introduced into the combustion chamber causing over speeding of the engine, the shut down device will prevent damage to the engine by cutting off the air supply and thus stopping the engine.

The shut down device consists of an air shut off valve (flap) mounted in the air inlet housing which is retained in the open position by a latch. A cable assembly is used to remotely trip the latch. The shut off valve must be manually reset on the latch for restarting the engine after the malfunction has been rectified.

6.4 Start up, operation and shut down

Start up checks
The checks and procedures to be carried out before starting an engine depend on

·      whether the engine has just been repaired or overhauled and
·      whether you were the last person to run the engine.




The person with the Certificate of Competency to operate the machinery of the vessel is the one who takes full responsibility and cannot transfer the blame if something goes wrong. To cover yourself, you must carry out pre-departure checks and checks whilst the vessel is under way.

The following checks apply to the main propulsion engine only and do not include any other piece of machinery or equipment that is checked during a pre-departure check.

Let us assume this is an air start engine and that the lubricating oil pump, fresh water cooling pump and the sea water pump are driven by electric motors.

Firstly, carry out all the necessary checks and procedures for starting the engine driving the alternator and putting it on the board (supplying electrical power to the vessel).

4
Checks to be made

Comments


Make sure that all work carried out on the engine has been completed, all guards are in place and that there are no tools, materials or parts lying on the engine.




Ensure that there are no rags on the engine, especially in the exhaust area. Check the whole engine is free from fuel and lubricating oil.




Gear box is in neutral.




Check the fresh water in the header tank is at the correct level.

Open the relevant valves. Start up the fresh water circulating pump and ensure there are no fresh water leaks. Apply heat to the fresh water and gradually raise the temperature.


Check the oil in the sump is at the correct level.

Open any relevant valves. Start up the lubricating oil pump and ensure there are no leaks. Apply heat to the lubricating oil and gradually raise the temperature.


If the fuel injection pump has its own sump, check the level in the sight glass is at the upper line.




If a turbo charger is fitted and has its own lubricating system, check the level in the sight glass is at the upper line.




Grease or oil any linkages.




Open the indicator cocks, where fitted.Indicator cocks are fitted to each cylinder to take indicator cards. Indicator cards allow the power of the cylinder to be assessed and identifies any problems in the cylinder

Opening the indicator cocks on this occasion allows the compression pressure to go to atmosphere. This allows the turning gear to rotate the engine easier. If the volume of any fresh water in a cylinder exceeds the clearance volume of the cylinder, it will discharge out the indicator cock while the engine is being rotated on the turning gear. This problem will have to be rectified before continuing further.


Engage the turning gear and switch the turning gear motor on.




Check the fuel filter is clean. Check there is sufficient fuel in the fuel tank for the intended voyage plus a reserve.

Open the fuel tank drain valve and drain off any sediment or water. Open the fuel tank outlet valve.


Prime the fuel system and bleed off any air.

This is not always necessary except after a repair has been carried out to the fuel system or long periods of shut down.


If a water separator is fitted, drain off any accumulated water.




Check the condition of any vee belt drives and that they are correctly tensioned.




Check the condition of all flexible hoses.




Check the movement of the hand throttle.




Ensure the air receiver/s are at their correct pressure.

If necessary, run the air compressor to bring them to the correct pressure. Drain off any water and/or oil from the air receiver.


Check that the sea water strainer is clean and open the sea connection valve and the overboard discharge valve.

Start up the sea water pump and ensure there are no leaks. The sea water will by-pass the fresh water and lubricating oil coolers until the temperatures rise above the normal operating temperatures.


Activate the alarm system.




When the fresh water cooling water and the lubricating oil have reached their operating temperatures, shut off the heat source.




Where fitted, stop the turning gear motor and disengage the turning gear.




Open up the air receiver stop valve to supply air to the starting air distributor.




Roll the engine over slowly on air at least one complete revolution to ensure there is no fresh water in any cylinder.

Any water will discharge from the indicator cocks. If there is water in a cylinder, the problem will have to be rectified before continuing further.


Place the fuel lever in the start position.




Engage the air start lever. As soon as the engine fires release the lever.

Listen for any unusual noises, especially hard metallic knocks.


Check for fresh water, sea water, lubricating oil, fuel oil and exhaust gas leaks.




With the engine at its operating temperature, check the colour of the exhaust gas.





Operational checks
It is assumed it is a manned engine room so all machinery will be monitored regularly.

4
Check:



Engine oil pressure.



All lubricating oil levels.



Engine fresh water temperature.



Fresh water level in the header tank.



For fresh water, sea water, lubricating oil, fuel oil and exhaust gas leaks.



Exhaust temperatures.



All flexible hoses for leaks and possible deterioration.



For any overheating.



Pumps circulating fresh water, sea water and lubricating oil. Electric motors driving them.



Listen for any unusual noises, especially hard metallic knocks.



Maintain the log book.



Use your senses when you carry out checks.

Smell

Hot oil, exhaust gas leaks, insulation melting on electrical cables, paint on an overheated surface and overheating problems give off individual smells that can be recognised. You can smell the combustion gases of a blown head gasket if blown between the cylinder and the outside of the engine.

Hearing

You can hear an injector pipe rattling in a clip. If you don’t stop it rattling, it will either wear through or fracture probably resulting in oil being sprayed onto the exhaust manifold and igniting. You can hear a metallic knock from a bottom end bearing with too much clearance. You can hear the pulsations of a blown head gasket if its blown between the cylinder and the outside of the engine.

Sight

As well as hearing the above mentioned injector piperattling, you can also see it rattling. Sight allows you to see most things that are wrong such as locking devices missing, excessive movement due to slackness or wear, etc. You can also see exhaust gas leaks, especially on starting an engine, before it fires. Soot deposits at a flange will also indicate an exhaust gas leak.

Feel

Placing your hand on a part will indicate its temperature. You will quickly learn what the normal temperature feels like, therefore overheating can be detected. You can feel the pulsations of a blown head gasket if its blown between the cylinder and the outside of the engine.

-


Shut down procedures
It is important that engine temperatures be reduced gradually to prevent unequal contraction of the different metals found in an engine. Otherwise cracking may occur in the block or cylinder head.

If an engine is fitted with a turbo charger, it is necessary to reduce its speed in stages or slowly for two reasons:

1.         Example: Engine speed is reduced from full engine speed to stop quickly. The bearings of the turbo charger are lubricated by the main engine driven lubricating oil pump. The engine, on stopping, will cease to supply the lubricating oil to the turbo charger bearings. Because of its high speed, it will take some time for the turbo charger to come to rest and the bearings could be damaged.

2.         The exhaust gas side of the turbo charger operates at a very high temperature. It is preferable to reduce the temperature gradually rather than quickly to prevent unequal contraction of the turbo charger parts as it slows down.

When the engine has been stopped
4

Checks to be made

Comments



Deactivate the alarm system.





Shut the fuel off at the tank.





Open the indicator cocks.





Engage the turning gear and start the turning gear motor.





Stop the sea water circulating pump. 
Shut the sea water intake valve.

On a lot of vessels, this valve is left in the open position from one survey to the next. This is bad and dangerous engineering practice. The purpose of the valve is to stop the ingress of sea water should a hose or pipe fail. If the valve is not worked (opened and closed) regularly, marine growth will make it difficult to close and impossible to seal.

A number of engine rooms have flooded, whilst no one was on board, because the sea valve was left open and a pipe or hose burst.

A notice should always be placed in a prominent position indicating whether the valve is opened or closed as a useful reminder in the pre-departure check.



Shut the sea water discharge valve.





Keep on circulating the fresh water and the lubricating oil and turning the engine until it cools down to the ambient temperature.





Switch off the turning gear motor.





Stop the fresh water and lubricating oil pumps and close any valves in the systems.





Close the indicator cocks.





If electrical power to the vessel is not required, shut down the engine driving the alternator.



6.5 Identifying causes for defects

·        Failure of engine to start
·        Low operating power
·        Exhaust emissions
·        Loss of lube oil pressure
·        Overheating of engines/components
·        Vibration
·        Fluctuation of engine revs
·        Crankcase explosions

There is a large amount  of information in this section. You may wish to work through certain areas at your own pace. Much of the text will be reference material to refer back to when these faults occur in your workplace.




Failure of engine to start
If the engine does not start, the causes are mainly in the supply of fuel and/or air.

Remember:

1.         A full charge of air needs to enter the cylinder.

2.         This air must not escape as it is being compressed. Otherwise insufficient heat is obtained to ignite the fuel.

3.         Fuel must be injected in an atomised form into the cylinder at a precise moment.

4.         In addition, there must be no restriction in the flow of exhaust gases.

An engine not turning over quickly when the starter motor is engaged could be caused by the following:

Cause

Comment

Battery capacity low

Check that electrolyte level is above the plates.

Try to start the engine on the other bank of batteries. Failing this, try to start the engine on both banks of batteries. Never continue to use a battery if the starter motor is sluggish. High discharge rates will buckle the battery plates.

Take the specific gravity of each cell of the battery. A fully charged battery would have a specific gravity reading in each cell of 1.26 where as a flat battery would give a reading of 1.10. The specific gravity reading should not vary more than 0.030 between cells. A lower reading on one cell usually indicates the battery needs replacing.

Batteryconnections dirty

Check that the connection to and on the battery is clean and tight. A dirty or loose connection can be identified by the heat it generates.

Bad electrical connection to starter motor

The starter motor draws the most load on the battery. This is especially so on diesel engines because of their high compression ratios. The electrical connections must therefore be tight and clean.

Faulty starter motor

The starter motor could be burnt out or the pinion is not engaging with the ring gear on the flywheel

Incorrect grade of lubricating oil

If the oil is too thick, the engine will not attain sufficient speed on the starter motor. In turn, this will not generate the amount of heat required on the compression stroke to ignite the fuel.

Engine has been overhauled and is tight

The parts of an overhauled engine are brought back to their correct clearances. In these clearances there will be a number of high spots. They will be worn away as the engine is run in. When the engine is run in, it will turn easily. The engine will not attain sufficient speed on the starter motor to generate the amount of heat required to ignite the fuel


There must be sufficient air and no restriction in the exhaust gas system:


Cause

Comment

Air cleaner restricted

The air cleaner is choked restricting all or most of the air required by the engine.

Exhaust gas restriction
Could be caused by a bucket left on the outlet of a vertical exhaust pipe to prevent rain water entering the engine; or by the automatic flap valve fitted for this purpose and is stuck in the closed position.

Occasionally a baffle could come loose in a silencer and block the passage of exhaust gas.



The air must be compressed to a high enough temperature to ignite the fuel.

This is usually due to low or poor compression. Compression pressure can be checked by replacing each fuel injector in turn with a compression gauge. Poor compression throughout the engine could result from one or more of the following:

Cause

Comment

Incorrect valve timing

The inlet valve is not opening or closing at the correct moment in the cycle. This is because the engine has not been correctly timed after maintenance work has been carried out. (The timing of the exhaust valve would be out as well.)

Worn cylinder liner bores

Normal wear takes place on the cylinder liner where the piston rings come into contact with it. The wear is more pronounced near the combustion space where the heat burns the lubricating oil. The wear is also oval due to the thrust of the piston on the cylinder wall. The piston rings will not seal against the cylinder liner walls and, on the compression stroke, air will pass the piston rings into the crankcase.

Cold engine
The air entering the engine and the piston, cylinder liner and cylinder head are so cold that they take away the heat of the compressed air before it can reach sufficient temperature to ignite the fuel. If an engine is fitted with heater plugs, they can be utilised. Other alternatives are to use an air heater or a starting fluid to assist ignition of the fuel.


There must be fuel.

Cause

Comment

Fuel tank empty

Fuel piping could develop a leak empting the contents of the fuel tank into the bilges.

Blocked fuel feed line

The suction valve on the fuel tank could have vibrated closed or someone could have closed the emergency fuel shut off valve.

Faulty fuel lift pump

Fuel is not being delivered from the fuel tank to the engine. If of the diaphragm type, the diaphragm could be perished or damaged. The drive to the pump could be damaged.

Choked fuel filter

The fuel filter has choked up with foreign matter preventing the full flow of fuel. The filter may not have been changed at its recommended period. A bad batch of fuel may have been received. The filter would require changing at more frequent intervals than recommended until the system is clean.

Air in fuel system

Air is compressible. Fuel is not. Air in a fuel system will cause the engine to malfunction or not start. Air usually enters the fuel system when repairs are carried out or where there is a fuel leak. This air must be bled off until a bubble free fuel is obtained. Some fuel systems have a manual priming handle on the fuel lift pump or on the fuel injection pump. In addition, there are bleed valves throughout the system, such as on filters or water separators.

Faulty fuel injection pump

The fuel pump is not delivering fuel to the injectors.

Incorrect fuel pump timing

The fuel is not being delivered to the fuel injector at the precise moment in the cycle. The engine could have been overhauled and the timing of the fuel pump was incorrectly carried out.


 Low operating power
Low operating power is caused by wear in the engine and combustion being incomplete. Therefore, fuel and air problems are involved. All in the following table result in lack of compression:

Cause

Comment

Restriction in air cleaner

Element is clogged restricting the flow of air into the engine. Replace element or clean air cleaner. If oil bath type, check cleanliness and level of oil.

Cylinder head gasket leaking

Could be leaking between two cylinders, between a cylinder and the outside of the engine or between a cylinder and a cooling water passage.

Fuel injector

The fuel injector body may not be sealing properly in the cylinder head allowing the compressed air to escape.

Air start valve

The air start valve may not be sealing in the cylinder head allowing the compressed air to escape.

Incorrect tappet adjustment

The tappet adjustment is such that there is no clearance between the inlet or exhaust valve stem and the rocker arm. The inlet or exhaust valve is not closing on the compression stroke. (Referred to as riding).

Sticking valves

The cam, through the cam follower, push rod and rocker arm, causes the valve to open. The spring causes the valve to shut when the cam follower moves off the lobe or peak of the cam.

A sticking valve is caused by combustion being incomplete. Alternatively, the engine may have overheated. Carbon finds its way between the valve stem and guide until the spring cannot exert sufficient pressure to close the valve. A broken valve spring will not close the valve. On the compression stroke, air will pass the valve. It could be an inlet or exhaust valve.

Pitted valves and seats

The exhaust valve and seat is more prone to being pitted. Carbon, from incomplete combustion, is hammered between the valve and seat when the valve closes. On the compression stroke, air will pass the valve.

Valves not seating correctly

Can be caused by the head of the valve being bent on its stem due to the head being too thin from continual grinding.

It can also be caused by exhaust gases scouring the valve face and/or valve seat in the head. On the compression stroke, air will pass the inlet or exhaust valve.

Incorrect valve timing

The inlet and exhaust valves are not opening and closing at the correct time in the cycle. Caused when the timing is being set. Check the timing marks are in line on the crankshaft and camshaft gearwheels or sprockets.

Worn cylinder bores



Normal wear takes place on the cylinder bores. This is especially towards top dead centre where the high temperatures of combustion tend to break down or burn the lubricating oil. The cylinder bores will also wear oval due to the thrust of the piston on the power stroke. Replace the cylinder liner.

Broken, worn or sticking piston rings

The piston rings expand and seal against the cylinder liner walls. Normal wear takes place and will in time become excessive. Piston rings are also subject to breakage in service or when installing. They will also stick in their grooves due to the carbon from incomplete combustion or overheating. In all cases air will pass the piston rings, on the combustion stroke, into the crankcase.

Piston ring gaps in line

Installation of the piston rings may have gaps which were not equally separated or the ring gaps came into line during the running of the engine. Piston ring gaps in line will cause the air from compression to enter the crankcase.

Turbo charger



Reduction in the turbo charger speed can be attributed to worn or faulty bearings or carbon build up on the exhaust gas turbine blades. This will cause a reduction in air supply to the air intake manifold resulting in a loss of engine power

Restricted fuel supply



Could be caused by fuel tank outlet valve not being fully opened. Vibration coupled with loose gland packing could cause it to start closing. The fuel tank vent pipe anti-flash gauze could be clogged. This will cause the fuel pump to pull a vacuum on the fuel tank. Open the outlet valve and tighten the gland packing. Clean the anti-flash gauze.

Faulty injector

Caused by blocked nozzle hole/s, valve not seating properly, broken spring, injector not opening at correct pressure, valve stem sticking in nozzle, leaking injector pipe, excessive fuel return. Replace the injector.

Faulty fuel pump

Caused by incorrect timing, wear between plunger and cylinder, delivery valve not seating properly, incorrect calibration, broken spring. Retime the fuel pump and if that is not the problem, replace the fuel pump.

Fuel lift pump

Fuel lift pump is not delivering sufficient fuel from the tank to the fuel pump. If of the diaphragm type, the diaphragm could be perished. In gear or plunger type pump it will most probably be wear. Overhaul the pump.

Fuel filter

Fuel filter could be blocked. Clean filter.

Water in the fuel

Drain the water from the fuel at the fuel tank and at the separator.

Restriction in flow of exhaust gases

Can be caused by excessive build up of carbon or a baffle plate in the silencer coming adrift and partially blocking the flow.

Restricted air supply

Could be caused by the fire flaps and hatch cover in the engine space being closed resulting in insufficient air flow to the engine.



Exhaust emissions
The colour of the exhaust gases can indicate problems with the engine.

Some electronic controlled fuel systems have the provision for the exhaust emissions to be monitored. It allows for the fuel metering and timing to be altered to suit the load and have the most efficient combustion possible.

Black smoke
indicates excessive fuel for the amount of air. It causes incomplete combustion and black smoke is emitted.  The problem may be:

·      Engine overload.
·      Blocked air cleaner.
·      Faulty injector/s.
·      Faulty fuel pump.
·      Incorrect fuel pump timing.
·      Incorrect valve timing.
·      Lack of compression.



Blue smoke

indicates lubricating oil is being burnt.  The problem may be

·      Worn cylinder liner/s.
·      Worn or faulty piston rings.
·      Excessive clearance in valve guides.
·      Oil seals in turbo charger not sealing.
·      If fitted, oil bath type air cleaner overfilled.

White exhaust vapour
indicates water or moisture.  The problem may be:

·      Water in the fuel.
·      Moisture in the air.
·      Cold cylinder liner bores when starting the engine.
·      Fresh water leak into the combustion chamber.

Loss of lubricating oil pressure
The reduction in the normal operating pressure of lubricating oil can be a gradual process or happen instantaneously. The loss of oil pressure will cause those parts under the most load to fail first. This would be the bottom end bearings, due to the load placed on them on the power stroke. By reducing the engine speed, the load on the bearings is reduced. If there is still some oil pressure there, the reduction in load maybe sufficient to save them.

Should the oil pressure drop instantaneously, the engine must be stopped immediately.

Problem
Comment
Recommended action
Insufficient level of oil in the sump

May cause a fluctuation of the oil pressure as the vessel rolls, the pump could lose suction and air enters it.
Reduce speed and top up the sump to the correct level.
Lubricating oil pump strainer clogged

Not much of a problem these days as the additives in the oil keep the foreign matter and sludge in suspension for the filter to remove. Will usually be a gradual drop in pressure..
If possible, clean the strainer
Faulty lubricating oil pump

If the drive to the pump has sheared, there would be no oil pressure at all. The engine must be stopped immediately otherwise severe damage could occur.
Should the gears or rotors or vanes of the pump be worn or too much clearance between them and the backing plate, there will be a drop in oil pressure, usually a gradual drop will occur.
Repair the pump.
Faulty relief valve

The pressure relief valve may be stuck in the open position or its spring may have broken. A cold engine, when started, will have a high oil pressure which will cause the relief valve to open. The engine’s oil pressure drops as the engine reaches its normal operating temperature and the oil thins out. This results in the relief valve closing. Should the relief valve stick in the open position or the spring breaks, the oil pressure will drop below normal.
Free up the sticking relief valve or replace the relief valve spring.
Filter partially blocked

With the filter being partially blocked, the flow of oil will gradually be restricted. Lower oil pressure will occur and be indicated on the pressure gauge until the filter by-pass valve opens.
Remember that most oil filters have a by-pass valve in them to prevent oil starvation in the event of the filter element becoming blocked. Whilst the oil flowing through the by-pass is not filtered, this is preferable to insufficient oil. When the by-pass valve opens, the oil pressure would return so the engineer should be aware of why the oil pressure has dropped slightly then increased.
Replace the filter element or clean the filter (centrifugal type).
Oil temperature too high

A high oil temperature will thin the oil out causing it to run more easily with a resulting drop in oil pressure. Could be caused by a worn engine which would have fresh water overheating as well. Alternately, it could be caused by a dirty oil cooler on the sea water side.
Run the engine at a slower speed until the normal operating oil pressure is obtained and voyage home. Alternately, clean the tubes in the oil cooler.
Faulty oil pressure gauge

A faulty oil pressure gauge could indicate a low oil pressure where in fact the actual pressure is correct
If the oil pressure gauge is suspected, try another one.
Fractured lubricating oil pipes

Will result in a gradual or sudden drop in pressure if the pipe splits.
Carry out repairs to rectify the leak.
Excessive clearance in a bearing or bearings

The small bearing clearance places a restriction on the flow of oil that  causesthe oil pressure. If the bearing clearance is excessive, the oil is less restricted and its pressure will drop below normal. Usually, a bottom end bearing will be the problem.
Providing the journal is all right, replace the bearing.
Water in the oil

Water mixing with oil will result in emulsified oil. It is grey/white or sometimes described as milky in colour. Emulsified oil looses its lubricating properties. When a certain amount of emulsification takes place, the oil pressure will drop below normal.
Stop the water leak and change the lubricating oil.
Fuel in the oil

Fuel contamination will thin out the oil and it will run easily off the dip stick. There will be a rise in the level in the sump. The dip stick will also have a fuel smell. Fuel contaminated oil looses its lubricating properties and the oil pressure will drop below normal.
Stop the fuel leak and change the lubricating oil.
Engine overheating
In determining the cause of an engine overheating, consideration should be given as to whether it is a gradual process or there is a sudden rise in fresh water temperature. 

An engine overheating can be identified by the fresh water cooling temperature gauge, the exhaust temperature and by the operators sense of touch.



Experience can develop a sense of touch by brushing the palm of a hand lightly over the parts of the cooling water system. It enables the operator to know exactly at what temperature each part works best and enables him or her to tell when there is a difference in operating conditions.

A gradual rise is where the temperature rises over a period of time caused by:

·      wear
·      a gradual build up of scale on the cooling water surfaces or
·      a sea water strainer gradually becoming clogged.

A sudden rise in temperature could be caused by:

·      the thermostat stuck in the closed position
·      a pump impeller revolving on its shaft or
·      the engine overloading.

When the engine is hot and the fresh water level in the header tank is low, cold water should be introduced very slowly whilst the engine is running. The cold water will then be heated sufficiently before it circulates around the combustion space. Cold water suddenly coming into contact with the hot cylinder liner and cylinder head may crack them.

You should also refer to Section 5.3 “Fault in the cooling system” which covers a number of reasons for the engine overheating.

In addition to the reasons listed in Section 5.3, you should consider the following:

Problem
Comment
Recommended action
Build up of scale on cylinder water jackets, etc.

Fresh water contains impurities and they come out of solution at high temperatures and will adhere to hot surfaces.

The hottest part of the engine is in the combustion space at the top of the cylinder. Scale will deposit on the cylinder liner walls in this area, on the passages to the cylinder head and around the exhaust valve.

The scale will stop the transfer of heat from the combustion process to the fresh water cooling and, in the case of passages, will restrict the flow. This will be a gradual process.
Reduce the engine speed until normal operating temperature is attained. The water passages will have to be chemically cleaned to remove the deposits.
Engine parts may be too tight causing friction
A new or overhauled engine normally runs hotter because it is tight. As the engine is run in, the high spots disappear and the engine turns easily. This reduces the operating temperature.
Reduce the engine speed so that it runs at its normal operating temperature.
Blown cylinder head gasket

Leaking between the cylinder and a cooling water passage will be indicated by bubbles in the header tank whilst the engine is running. The extent of the leak will determine the amount of bubbles. When checking for bubbles, remember the above for pressurised and unpressurised systems.

Whilst the engine is running, the pressures inside the cylinder exceeds that of the leak and the water. The heat will turn the water into steam and be discharged with the exhaust gases. However, when the engine is stopped, there is no pressure in the cylinder. The header tank is above the cylinder thereby putting  pressure (a head) on the water. The water would then flow through the leak in the cylinder head gasket into the cylinder.

Should the piston be below top dead centre, sufficient water could flow into the cylinder and hydraulic it.
The water level would drop in the header tank and the procedure would be the same as that above. However, remember that if the engine is stopped for a period of time, it may hydraulic the cylinder.
Low compression

Low compression causes the engine to overheat. Some of the heat in the combustion gases by-passes the piston rings and goes into the crankcase. The cooling water is not taking away the heat caused by combustion and overheating of the engine occurs.
The engine speed should be gradually reduced until the normal operating temperature is attained. Rectify the cause of low compression.
Engine overloaded
An engine that is overloaded will overheat. An engine can be overloaded by a dirty hull, a rope around the propeller, a bent propeller blade or too large a pitch propeller.
The engine speed should be reduced until the normal operating temperature is attained. To stop overheating, it would be necessary to clean the hull of marine growth, remove the rope from the propeller, straighten the propeller blade, alter the propeller pitch or replace the propeller with one of the correct pitch.
Fuel injection into cylinders may be too late

The timing of the fuel injector pump is out causing the fuel to be injected into the cylinders too late. This will cause the engine to overheat.
Reduce engine speed until normal operating temperature is attained. Stop engine and adjust fuel pump timing.


Vibration
Vibration is a back and forth movement and may only appear at certain revolutions of the engine. It is usually the result of some component being out of balance like the rotor shaft of a turbo charger.

The crankshaft of an engine can be fitted with a vibration damper or harmonic balancer. They reduce the quick increases in crankshaft speed caused by the firing impulses of the cylinders anddampens out the crankshaft vibration.

Flexible engine mounts that have lost their resilience will also cause vibration.

When the engine is not lined up with the shafting (intermediate or propeller), vibration will occur.

A damaged or bent propeller blade or a rope caught around the propeller will cause vibration.

A misfiring engine will cause vibration.



Fluctuation of engine revolutions
Fluctuations in the engine speed can be caused by the governor.

A hydraulic governor should be checked for sufficient supply of oil, that dirt has not entered the oil spaces, the linkages are not binding or have excessive wear.

A mechanical governor should be checked that the lubricant is sufficient, and that the linkages are not binding or have excessive wear.

Fluctuations in the engine speed can also be caused excessive engine load and the governor not being able to cope.

Intermittent misfiring can also cause speed fluctuation. This would usually be caused by a faulty fuel injector.

Crankcase explosions
The three components which cause fire are fuel, oxygen and heat. In an engine crankcase, there is fuel and oxygen. Only heat is required for an explosion to occur. The fuel is in the form of a mist of lubricating oil. If there is fuel contamination, the risk is higher. Heat can be supplied from a hot bearing, combustion gases passing the piston rings (blow by) or by partial seizure of a piston with its cylinder liner. When the three components come together, an explosion will occur.

An engine may be fitted with a crankcase relief valve to relieve any violent increase of pressure in the crankcase. They are so constructed as to open smartly and close promptly and decisively. Closing promptly ensures a minimum of fresh air enters the crankcase which might cause a further explosion.

A hot bearing is caused by insufficient clearance or lack of lubrication. The journal may have to be ground. A new slipper bearing would be required.

“Blow by” is caused by worn liner and/or piston rings. Replace the worn parts.

Partial seizure of a piston with its cylinder liner is caused by overheating which also causes a reduction of lubrication in the cylinder. Depending upon the degree of pick up, a severe case will require the cylinder liner and piston to be replaced.

Engine oil diluted by fuel will result in the oil thinning out and loosing its viscosity. Stop the fuel leak and replace the oil. As stated previously, oil diluted by fuel increases the chances of a crankcase explosion.


6.6 Engine room log book

An engine log book assists in trouble shooting and the maintenance of all machinery providing the relevant details are entered regularly.

Where vessels are required by law to maintain a log book, they can be used in an investigation into an incident. A log book is therefore an official document, and to be completed in accordance with the instructions given.

Where a vessel is not required to maintain a log book, it is still good engineering practice to maintain records of all service and maintenance work carried out.

A log book has the advantage that amongst other things, relevant pressures and temperatures are recorded regularly. For example, where a temperature is recorded every four hours, a pattern may emerge that it is steadily rising but the sea temperature remains constant. You would need to exercise your judgement as to why this trend may be occurring.

Engine manufacturers issue a maintenance schedule for each model of engine. The suggestions and recommendations for preventative maintenance should be followed as closely as possible to obtain long life and best performance. However, the periods between inspections are a guide only as a lot depends on the operating conditions of the engine. Certain parts may need to be inspected at more frequent intervals, whilst the condition of the parts may indicate that longer running periods may be allowed.

Therefore, records should also be kept of all maintenance carried out, the running hours and date at which it was carried out. Records should also be taken of any measurements. For example, if the piston rings are renewed, but the liners measured are found to be within tolerances stated by the manufacturer, the measurements taken shall be recorded so the rate of wear can be ascertained. It can be calculated in running hours when the wear will exceed the tolerances. The engine log will indicate the operating conditions of the engine during any particular period. 

Technology is heading in the direction, and is already fitted to vessels, that computers through sensors regularly scan all important points of an engine. A read out or a print out can be given.Service intervals can be set so maintenance is only carried out when needed. The computer can tell the operating conditions of the engine and where the critical wear and tear is or has taken place.


6.7 Preventative maintenance schedule
Preventative maintenance schedules are laid down to ensure the continued trouble free performance of the engine and to maintain it in tune.

Wear will occur in any engine. It should be rectified at regular intervals rather than allow it to accumulate until the inevitable breakdown occurs.

Engine manufacturers issue a maintenance schedule for each model of engine. The suggestions and recommendations for preventative maintenance should be followed as closely as possible to obtain long life and best performance. However, the periods between inspections are a guide only as a lot depends on the operating conditions of the engine.

The maintenance periods are usually expressed in running hours. However, most manufacturers recognise that some engines will do less running hours in a given period than others. An engine that is not used regularly will have its own problems. Therefore manufacturers also specify time periods to overcome these problems.

On the following page, a simple maintenance schedule is shown. This schedule does not go into depth, such as when the cylinder head should be removed. The maintenance schedule indicates which part needs cleaning, changing, checking, etc. Reference should be made to the Operators Manual for detailed instructions. These instructions deal with procedures, cautionary measures and useful hints. Such instructions help to carry out the work quicker and safely.

The Chart also gives specifications for the fuel, oil, grease and coolant. It also refers to other information for more complete and detailed instructions.

The following is the maintenance recommendations for Caterpillar 3500 marine engines.

Lubrication and Maintenance Chart
Item
Procedure
Lubricant
Every 10 Service Hours


Engine
Inspect engine for leaks and loose connections

Engine Crankcase
Check the oil level - add oil if needed
EO
Cooling System
Maintain Coolant level

Air Starter (if Equipped)
Check air starter lubricator oil level - add oil if needed
EO (SAE 10W)
Clutch shift collar
Lubricate 1 fitting
MPGM
Fuel and Oil Differential Pressure
Check the fuel filter and oil filter differential gauges

Woodward UG8L Governor (if Equipped)
Maintain oil level
EO
Every 50 Service Hours


Zinc Rods
Inspect - replace zinc rods (sea water applications)

Every 125 Service Hours


Shift Lever Bearings
Lubricate 2 fittings
MPGM
Pilot Bearing
Lubricate 1 fitting
MPGM
Main Shaft Bearing
Lubricate 1 fitting
MPGM
Clutch
Check - Adjust if required

Every 250 Service Hours


Cooling System
Add Caterpillar cooling system conditioner or replace coolant conditioner element (if Equipped)

Batteries
Maintain electrolyte level. Clean top of batteries and cable connections

Engine Crankcase (See Note On Reverse)
Change oil and oil filters. Take sample for S·O·S analysis. See Oil and Oil Filter Change Interval Chart
EO
Belts
Inspect all belts for wear and proper adjustment

Hoses
Inspect all hoses for wear and loose connections

Fuel tank
Drain water and sediment

First Oil Change Interval
New/Rebuilt Engines
Inspect - adjust valve lash. Observe rotation of valves. Inspect - adjust injector timing

Every 1000 Service Hours
Fuel System
Clean primary fuel filter. Change final fuel filters.

Woodward UG8L Governor (if Equipped)
Change oil in Woodward governor
EO
Breather
Clean crankcase breather elements

Governor (Air Actuator)
Lubricate 2 fittings
MPGM
Shutoff Controls
Inspect engine shutoff controls. The shutoff controls must be inspected periodically so that they will function properly when required. Only authorised personnel should perform the inspection. Contact your Caterpillar dealer.

Every 2000 Service Hours
Valve lash
Inspect - adjust valves. Observe valve rotation.

Jacket Water Thermostats
Inspect - Replace if necessary.

Turbochargers
Inspect turbochargers.

Engine Mounts
Inspect engine mounts for damage. Check bolts for proper torque.

Damper
Inspect damper for damage.

Every 4000 Service Hours
Cooling System
Drain and clean cooling system. Add coolant conditionerprecharge.

6.8 Safety aspects when working on engines

Safety is a very important consideration in all industries. Your workplace is no exception. The following information is a summary of safety considerations. (You may wish to re-visit information in the “Occupational Health and Safety at Sea” module presented in the MED2 modules).

Safety, when working on engines, can be divided into a number of areas.
·      Being caught in rotating machinery.
·      Fire precautions.
·      Oil causing slippery conditions.
·      Heat causing burns or scalding.
·      Ensuring satisfactory completion of work.

Being caught in rotating machinery
When you are working on an engine, ensure that the engine cannot rotate. Such an occurrence usually results in the loss of fingers. There are various ways in which an engine can be rotated, depending on the size, method of starting and number of propellers.

Advise personnel that work is being carried out on an engine. Be aware of any personnel not present at the time of the instruction, so they can be advised.

Place a warning sign or signs in the relevant positions where the engine may be rotated. There was a case where an engineer ignored a warning sign not to start an engine (direct reversible type), started it and cut a diver, who was in the propeller aperture, to shreds.

Disconnect the source of supply to the method of rotating the engine. eg. disconnect batteries, tie up the air receiver stop valve.

You, as the person in charge, may have someone else (a fitter or mechanic) carrying out maintenance work. Under the Occupational Health and Safety Act, you are the one responsible for any safety issues involved. Stiff penalties are prescribed.

A vessel may have one engine driving a propeller and making way through the water whilst the other engine is stopped. The vessel moving through the water can cause the stationary propeller to revolve and turn the stationary engine. In this type of situation a shaft brake would be fitted and should be applied and the turning gear engaged.

Fire precautions
You are aware that fuel dilution of the lubricating oil is taking place and suspect a leaking injector pipe under the rocker cover.

With the engine stopped, the rocker cover is removed. There is no indications of which pipe is leaking. There is no provision to bar the engine over, so it is necessary to start the engine to locate the exact position of the leak.
In starting the engine, it is possible for fuel to spray in any direction as the rocker cover is not containing it. Should it spray onto a hot surface, it could ignite. In addition, it could spray into a persons face and due to its high pressure, cause eye damage. Eye protection should be worn.

One person should start the engine and stop it as soon as it fires, while the other person locates the fuel leak.

Remember, the valve rocker gear will be operating so make sure no part of your clothing, hair, part of your body, rag in the hand can get caught.

In addition, oil will be splashed over the engine.

Oil causing slippery conditions
When working on an engine, it is difficult not to have patches of oil lying about. Oil could cause you to lose your grip or footing and sustain injury. Any spilt oil must be cleaned up immediately.

Heat causing burns or scalding
Being burnt on a hot exhaust pipe is bad enough, but being scalded by hot water is serious. The engine may have overheated. Working on the cooling water system before the engine cools down is dangerous. Equally dangerous is removing the cap on the cooling water header tank before releasing the pressure in the tank.

Ensuring satisfactory completion of work
When any work has been carried out on an engine, a check should be made to ensure that the work has been completed and that there are no tools or rags lying in, around or on top of the engine before a test run is carried out.

Completing the work means that all connections, couplings, flanges, components, etc. have been tightened up, all locking devices are in place, access doors and guards are back in place, plus oil and water levels are satisfactory.

Failure to take these precautions could result in fire, or maybe damage to the engine and injury to personnel should a component come adrift. 

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