Engineering question bank — Mashit 30

All 178 questions of the paper, arranged by topic, with the correct answer. For searching, browsing and revising before the exam.

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Engine principles — 17 questions. Internal combustion, compression ignition, strokes and pressure charging
Engine parts — 16 questions. Piston, crankshaft, valves and flywheel
Fuel system — 27 questions. Injection, injectors, fuel supply, filters and bleeding
Lubrication and oil — 21 questions. Oil pressure, oil level, filters and lubrication faults
Cooling system — 18 questions. Fresh water and raw water, thermostat, heat exchanger and temperature
Pumps — 11 questions. Centrifugal, piston, Jabsco-type and bilge pumps
Electrical system — 23 questions. Battery, alternator, starter motor and fuses
Propulsion and propeller — 15 questions. Gearbox, shaft, pitch, diameter and thrust
Operating routine — 9 questions. Checks before and after starting, shutdown and the control panel
Fault-finding — 11 questions. An engine that will not start, stops, misfires or overheats
Safety and fire — 3 questions. Fighting an engine-room fire and conditions for ignition
Calculations and units — 7 questions. Power, volume, horsepower and temperature conversions

1.1 Working principle and ignition

What is the main characteristic of a diesel engine? An internal-combustion engine with compression ignition.
How is the fuel ignited in a diesel engine? By the heat produced by compressing the air.
What does the piston compress in a diesel engine? Air only.
What happens during the compression stroke of a diesel engine? The pressure and temperature of the air rise.
What is the fundamental difference between a petrol engine and a diesel engine? All of the above.
How does the fuel ignite in a diesel engine? It ignites on contact with the compressed air and the heat in the cylinder.
What ignites the fuel in the combustion chamber of a diesel engine? The very hot air compressed in the cylinder.
What ignites the fuel in a two-stroke petrol engine? An electric spark plug.
What is the operating principle of a petrol engine? Internal combustion and spark ignition.

1.2 Two-stroke, four-stroke and pressure charging

What is the function of the scavenge blower in a two-stroke diesel engine? To supply "fresh" air under pressure to the cylinder, to clear out the exhaust gases and for combustion.
What closes the inlet ports in a two-stroke petrol engine? The piston.
What is the order of the strokes in a 4-stroke diesel engine? Intake, compression, power, exhaust.
What is the main function of the scavenge blower in a 2-stroke diesel engine? To force fresh air into the cylinder, in place of the intake stroke of a 4-stroke engine.
What is the function of the turbocharger in a 4-stroke diesel engine? To increase the engine's power output.
The inlet ports in a two-stroke petrol engine are closed by: The piston.
What does "supercharging" (turbocharging) mean? Getting a greater weight (mass) of air into a cylinder of a given volume.
In a two-stroke petrol engine, which part closes the air inlet ports? The piston.

10. Units and calculations

What is the unit of power? Watt.
In which units is "power" measured? All of the above.
What is the volume of one cubic metre of water? 1,000 litres.
A quarter of a cubic metre of diesel is left in the tank. The engine uses 8 litres of fuel an hour. Roughly how much longer can the engine run? 31 hours.
The temperature is 176°F. What is it approximately in °C? 80°C.
5 cubic metres of water are equal in volume to: 5000 litres.
A power output of 250 horsepower is approximately equal to: 186 kW.

2.1 Piston, rings and cylinder

What are the functions of the piston rings? To seal the gap between the piston and the cylinder.
What is the function of the piston? To convert the combustion pressure into linear motion.
Why is the diameter of the piston smaller than the bore of the cylinder? To allow for thermal expansion.
What is the name of the lowest point the piston reaches during operation? Bottom dead centre.

2.2 Crankshaft, connecting rod and flywheel

What is the main function of the crankshaft counterweights? A centrifugal balancing force.
How does the engine's construction change as the number of cylinders increases? The flywheel becomes smaller in proportion to the number of cylinders.
What is the main function of the flywheel? To store momentum and keep the rpm steady between the strokes of the working cycle.
What are the main functions of the crankshaft? To convert linear motion into rotary motion.
What are the pistons and connecting rods of the engine connected to? To the crankshaft.
What is the function of the connecting rod? To connect the piston to the crankshaft.
What is connected to the two ends of the crankshaft? The gearbox, through the flywheel, at one end, and a belt pulley at the other.

2.3 Valves, timing and air intake

What can happen if the valve (tappet) clearance is too large? Noisy running and a loss of power.
What can too small a valve clearance cause? Burning of the exhaust valve.
Which mechanism operates (times) the valves? The camshaft.
Where is the air filter fitted on a diesel engine? On the inlet manifold.
What is the purpose of the "clearance" between the valves and the rocker arms? To allow for thermal expansion of the valve gear.

3.1 Injection pump and injectors

What is characteristic of the fuel pipes from the injection pump to the injectors? They are all the same length.
What is the function of the fuel injector? To spray fuel into the combustion chamber.
Which part of the fuel system determines how much fuel is injected in a diesel engine? The injection pump.
What is the function of the injection pump? To deliver fuel under pressure, correctly timed, to the injectors.
What is the function of the injector in a diesel engine? To break the fuel up into a fine spray and spray it into the combustion chamber.
What is the main purpose of the fuel system in a diesel engine? To spray fuel into the combustion chamber with precise timing and in a precise quantity.
What is generally true of the pipes that carry fuel from the injection pump to the injectors? They are usually all the same length and withstand high pressure.
What is the function of the injection pump? To deliver fuel to the injectors at high pressure, in varying quantities and with precise timing.

3.2 Tank, fuel supply, filters and bleeding

What type of lift pump is commonly used in an engine's fuel system? A diaphragm pump.
What is the function of the lift pump in the fuel system? To help with bleeding (priming), and to transfer fuel from the fuel tank to the injection pump.
Where is the lift pump usually fitted in the fuel system? Between the tank and the fuel filter.
How do you check whether fuel is reaching the injection pump? Open the air bleed screw at the pump outlet.
What can the sediment in the fuel system consist of? Solid particles.
When is the risk of an explosion in the fuel tank greater? When the tank is almost empty.
What sediment is usually found in the fuel tank of a diesel engine? Bacteria and fungi that have grown in the fuel tank.
What is the purpose of the vent pipe fitted to the fuel tank? To let the tank breathe and keep the pressure in the tank equal to atmospheric pressure.
If a diaphragm-type lift pump is not pumping, what could be the cause? All of the above.
What is the most common fault in diesel engines? Air getting into the fuel system.
What is the purpose of the vent (breather) fitted to the fuel tank? To let the tank "breathe", balancing it with air, when refuelling or when fuel is drawn off.
What should you do after finding air in the fuel system? Bleed the air out of the fuel system.
What is needed to "prime" (bleed the air from) the injector pipes? Turn the engine over continuously (the crankshaft) and slacken the pipe unions at the injectors.

3.3 Power control and the governor

How is the engine speed of a diesel engine changed? By controlling the governor.
What does a change in a diesel engine's power output depend on? The quantity of fuel injected.
What is the function of the governor in a diesel engine? To keep the engine running at the desired, steady speed.
What does the stop handle control? The governor.
What does the throttle lever control? Answers a and c are correct.
What is the function of the governor in a diesel engine? It keeps the desired engine speed (rpm) by acting on the injection pump.

4.1 Oil, pressure and lubrication

How is pressure lubrication carried out? By an oil pressure pump.
Where in the engine is the oil pressure measured? After the oil filter.
Where is the oil collected in a diesel engine? In the sump.
Why is the oil pressure high just after the engine is started? The oil is cold and more viscous.
When is the oil pressure higher? When the engine is started from cold.
What is the main job of the oil in the engine? To reduce wear and friction.
How can you check the amount of oil in the sump? With the dipstick.
How are the engine parts lubricated in a two-stroke petrol outboard engine? By oil mixed with the fuel.
When should the engine oil level be checked? Before starting the engine.
What are the functions of the oil in the engine? All of the above.
What is the role of the lubricating oil in the engine? All of the above.

4.2 Oil condition and lubrication faults

What does "milky oil" (an emulsion) in the engine indicate? Water in the oil.
What colour of engine oil shows that water has got into it? Whitish.
What can a rise in the oil level in the sump indicate? Fuel getting into the oil.
After running under load, while you are coming alongside the quay and have reduced the engine rpm, the oil pressure warning comes on. What should you do? Finish mooring quickly and then stop the engine.
While checking the engine oil you find it is black. What should you do? Nothing: one of the oil's jobs is also to absorb soot particles.
Why does every engine lose lubricating oil as it runs? Because some of the oil that lubricates the piston rings is eventually burnt.
What can cause "thin oil" in an engine? Fuel getting into the oil.
What symptoms result from a dirty oil filter? A drop in oil pressure.
What should you do if the low oil pressure warning comes on? Stop the engine immediately.
When will the oil pressure be lower than normal? When there is not enough oil in the system.

5.1 Cooling systems and the heat exchanger

In a closed cooling system, what is the function of the engine's fresh-water (treated water) pump? To use the water to carry the engine's heat to the raw water, through the heat exchanger.
What is the function of the raw-water pump in a closed cooling system? To supply water to cool the fresh-water system.
What characterises a combined (closed) cooling system? The engine is cooled by treated water, which is in turn cooled by raw (sea) water.
Which type of cooling system has cooling fins and a radiator? An air-cooled system.
What is the purpose of the pencil zincs (zinc rods) in the raw-water cooling system? To prevent galvanic corrosion of the parts of the raw-water system.
What is the purpose of the valve in the cap of the header (expansion) tank? To keep the water in the system at high pressure and raise its boiling point.
A heat exchanger (cooler) is typical of which type of cooling system? A closed cooling system.
What is the main job of the coolant pump in the fresh-water system? None of the above.
You have started the engine and find that no water is coming out of the exhaust. What could be the cause? The seacock (raw-water inlet valve) is closed.

5.2 Thermostat, temperature and cooling faults

The temperature gauge of a diesel engine reads 213°F. What should you do? The engine is boiling: stop it and find the cause.
The engine's coolant temperature gauge reads 180°C. What does this mean? The gauge is probably faulty.
What does the temperature gauge on a diesel engine normally measure? The temperature of the water leaving the cylinder head.
What should you do when the engine overheats? Reduce the load and find the fault.
In a closed cooling system, what can cause a large and rapid loss of coolant? The engine overheating and boiling.
What is the purpose of the thermostat in the engine's cooling system? To let the engine run at a steady, constant temperature.
The thermostat in the cooling system has stuck open. What could the effects be? Over time it will cause damage, because the engine will run below its recommended temperature.
How often is it recommended to check the coolant level? Before each time the engine is run.
Where is the thermostat usually fitted in the engine's cooling system? At the coolant outlet from the cylinder head.

6. Pumps

What is the basic purpose of a centrifugal pump on an engine? Pumping water.
What can a piston pump do? It can pump air and liquids.
What is the working principle of a piston pump? Changing volume.
Which positions must the operating switch of an automatic bilge pump have? Off, manual, automatic (float switch).
What is the most common fault in a raw-water pump? A blocked suction inlet.
What is the working principle of a centrifugal pump? The rotation throws the liquid outwards, against the walls of the pump casing.
What is a portable submersible pump commonly used for? Pumping bilge water in an emergency.
On what principle does a rubber-impeller pump (Jabsco) work? Changing volume.
Why might a centrifugal bilge pump be unable to discharge the water overboard? The hydrostatic pressure at the discharge is too high.
The suction is free of blockages, but the centrifugal pump cannot pump. What is the cause? Air is getting into the suction line.
What will happen if you run a Jabsco pump with the valve on its suction side closed? The impeller will burn and be damaged.

7.1 Battery and charging

What liquid is added to a battery? Distilled water.
What kind of electric current does a battery supply? Ordinary direct current.
How can you tell the positive terminal of a battery from the negative one? The positive terminal is thicker.
What does a hydrometer measure? The density of the electrolyte in the battery.
If it is not marked, how can you tell what voltage a battery can supply? By the number of cells.
In what units is battery capacity measured? Ampere-hours.
What is the function of the battery on board a vessel? To supply electrical energy to run the electrical systems.
In daytime, with the engine running and no electrical loads switched on, the ammeter shows 5 amperes for a long time. What does this mean? There may be a current leak or a short circuit in the electrical system.
Why must you not smoke near a battery that is being charged? The hydrogen given off by the battery while charging may explode.
What must you check when charging a battery? That the vent holes in the caps are open.
In what units is battery capacity measured? Ampere-hours.
With the navigation lights on, the voltage measured across the battery terminals is 10 volts. What does this mean? The battery is weak and probably faulty.

7.2 Starter motor, alternator and circuits

Which gearwheel does not turn while the engine is running normally? The starter-motor gear.
How does the electric starter motor turn the engine? Through gear wheels.
Do you need to run the engine to use the electric anchor windlass? It is advisable, to help supply the current.
What protects the electrical system against overload? The fuse.
What should you do when the alternator's output voltage is unsteady? Check the alternator drive belt.
When the VHF radio is switched on and transmitting, the voltmeter drops from 13.5 volts to 12.5 volts. What does this mean? The batteries are in good condition.
Where does the starter motor get its electrical power from? From the battery.
What can a slack engine belt cause? Poor battery charging.
What protects electrical equipment from overcurrent or a short circuit? The fuse.
When you try to start, the starter motor clicks but the engine does not turn. What could be the cause? All of the above.
When you try to start, the engine turns over too slowly and does not "start". What is a possible cause? The battery terminals are not properly connected, or the battery is weak.

8.1 Gearbox, shaft and stern gland

What transmits most of the propeller's thrust to the vessel? The tapered end of the shaft.
How is the vessel's movement changed from "ahead" to "astern"? By reversing the direction of rotation of the propeller shaft.
What is the function of the zinc anode fitted to the bottom of the vessel? To prevent electrolytic corrosion of metal parts in the water.
What is the main purpose of the "key" at the end of the propeller shaft? It is used mainly to lock the propeller to the shaft and keep it secure.
What is the main function of the gearbox on most vessels? To allow the direction of rotation of the propeller shaft to be changed.
What is the function of the thrust bearing in the propeller shaft system? To transmit the propeller's propulsive force to the vessel.
How is the engine's gearbox lubricated? With gearbox oil.
How is most of the torque transmitted from the shaft to the propeller? By the tapered (conical) end of the shaft.
What signs may show that the propeller shaft is out of line (misaligned)? All of the above.
What is the purpose of the stern gland (stuffing box) on the propeller shaft? To stop sea water entering the vessel through the opening where the propeller shaft passes out to the sea.

8.2 The propeller — diameter, pitch and thrust

What will be the effect of replacing the propeller with one of greater pitch? The load on the engine will increase.
What does the blade area of a vessel's propeller affect? The amount of thrust delivered to the vessel.
What will happen if we replace our vessel's propeller with one of the same diameter but a smaller pitch? The load on the engine will decrease.
What does the pitch of a propeller indicate? The theoretical distance the vessel advances in each revolution.
What does the diameter of the propeller mainly affect? The amount of thrust delivered to the vessel.

9.1 Routine operation, checks and shutdown

What must be done before starting the engine? Put the systems in neutral (disengaged) and check the fluids.
What must be done after starting the engine? Check the oil pressure and that cooling water is being discharged overboard.
How is a diesel engine normally stopped? By cutting off the fuel supply with the governor.
What must be checked immediately after starting the engine? Oil pressure, cooling-water flow, charging current.
What are the essential spare parts for a diesel engine? Injectors, belts, impellers, seals, filters.
How is a diesel engine normally stopped? By cutting off the fuel supply with the control rod linked to the governor.
Which indications must the engine control panel show? Oil pressure, engine temperature, engine rpm.
What must be checked before starting the engine? Oil level, fuel quantity, coolant level and engine in neutral.
What do you normally do to stop a diesel engine? Cut off the fuel to the injectors by pulling the stop handle, which is linked to the governor.

9.2 Fault-finding

What will make a diesel engine run irregularly? Air getting into the fuel.
When you try to start a diesel engine, it turns over well but does not start. What could be the cause? No fuel is reaching the injectors.
You started a diesel engine and after a few minutes it stopped by itself. What could be the cause? Lack of fuel or a fault in the fuel system.
Why is it undesirable to run the engine at low speed for long periods? Soot may build up on the piston, the valves and the injector tip.
By which signs can you tell that the engine is overloaded? Coolant temperature too high and black smoke from the exhaust.
While the engine is running it starts to "stutter". What could be the cause? The fuel tank has probably run dry and the lift pump is drawing in air as well.
While underway, the tank runs out of fuel and the engine stops. What is the next step? Refill the tank and bleed the air from the fuel system.
When you start the diesel engine, it turns over but does not start. What could be the cause? There is air in the fuel system.
What should you do if the speed of a diesel engine rises out of control? Stop the engine immediately by choking off its air supply.
The engine runs normally in neutral but stops when you engage ahead gear. What do you think has happened? A rope or plastic sheeting has fouled the propeller.
What is one of the conditions needed to start a diesel engine? The crankshaft must be turned fast by some means.

9.3 Safety and fire

What can a hole in the engine's exhaust pipe cause? Exhaust gases escaping into the inside of the vessel.
How should you put out a fire in the engine compartment? Shut off the fuel, close the vents to smother the fire, and discharge an extinguisher through a narrow opening.
What basic conditions are needed for a fire to start? Flammable material, oxygen, heat.