Mechanics

Question 1

name the strokes of a 4 stroke engine

Answer 1

1. induction
2. compression
3. power also called the explosion or combustion
4. exhaust

Question 2

what happens on the induction stroke?

Answer 2

intake valve open
exhaust valve closed
the piston descending
lastly a mixture of petrol and air is drawn in the cylinder

Question 3

what happens on compression stroke?

Answer 3

intake valve and exhaust valve closes

piston moves upwards from “bottom dead centre” to “top dead centre”

compresses the mixture to about 1/6 of the original volume.

Question 4

what happens on power stroke?

Answer 4

as the piston reaches top dead centre:
the spark plug ignites the compressed mixture and
the pressure forces the piston downwards, which transmit the power through the connecting rod to the crankshaft
also, both shaft will be closed.

Question 5

what happens on the exhaust stroke?

Answer 5

as the piston reaches the “dead bottom centre”
the exhaust valve opens
while the piston is returning towards the “top dead centre”
it expels the burnt mixture out of the cylinder through the
open exhaust valve.

Question 6

what is the use of the crankshaft?

Answer 6

the main shaft of the engine which permits the backwards and forward movements of the piston by the means of
connecting rods and big-end bearings.
this movement is converted to rotary movement
it also drives the camshaft at half of the engine speed
by the means of a timing gear or chain.

Question 7

what is the use of the camshaft?

Answer 7

it operates the valves and

drive the mechanical fuel pump, oil pump, and the distributor shaft

Question 8

how is the valve opened and closed?

Answer 8

the camshaft opens the valve and

the pressure of the valve spring closes it.

Question 9

what is the use of the piston?

Answer 9

to transmit power to the engine

Question 10

what is the use of the connecting rod?

Answer 10

to transmit movement between the crankshaft and piston.

it couples the piston to the crankshaft by the means of the

• big-end bearings and
• Gudgeon Pin

Question 11

what is the use of the fly wheel?

Answer 11

the fly wheel is attached to the back-end of the crankshaft.
because of its weight it provides continuous movement of the crankshaft momentum.
eg. when the piston is down, the fly wheel will cause the piston to travel to the top without the aid of the engine’s power.

the ring gear is attached to the outer edge of the fly wheel.

Question 12

what operates the piston ?

Answer 12

the internal combustion of the engine with

the aid of the continuous momentum of the fly wheel and crankshaft.

Question 13

name the two types of valves in the engine

Answer 13

intake valve

exhaust valve

Question 14

how many valves are there in a four cylinder engine?

Answer 14

2x4

8 valves

Question 15

what is the combustion chamber?

Answer 15

it is the space between the piston and cylinder head

when the piston reaches the end of its stroke “top dead centre”

Question 16

what is the use of the ring gear?

Answer 16

when the starter button or lever is pressed, the starter gear meshes with the ring gear to supply the revolutions necessary for starting the engine.

Question 17

firing order

Answer 17

4 cylinders = 1,3,4,2 or 1,2,4,3
6 cylinders = 1,5,3,6,2,4 or 1,4,2,6,3,5
8 cylinders = 1,6,2,5,8,3,7,4 (straight eight)
V. 8 = 1,5,4,8,6,3,7,2

Question 18

how many types of piston rings are there and

what are their uses?

Answer 18

2 rings.

compression rings= to prevent gas or air escaping from the combustion chamber.

oil rings= to prevent oil being pumped up into the combustion chamber.

Question 19

what is the main difference between a gas and a diesel engine?

Answer 19

the gas engine= has a carburettor that mixes petrol and air, which is supplied to the combustion chamber where it is ignited by the spark ring.

the diesel engine= has NO carburettor therefore no ignition system.
the fuel oil is injected into the combustion chamber on the compression stroke . At that moment, the air is so highly compressed that it creates an explosion which drives
the piston down.

Question 20

what is an internal combustion engine?

Answer 20

it is the type of engine that uses petrol or fuel oil
which is ignited inside the cylinders

eg. the motor car or the diesel engine.

Question 21

what is the use of the fan?

Answer 21

to assist in sucking air through to the radiator for cooling the engine.

Question 22

what are water jackets?

Answer 22

they are spaces around the cylinders through which the water circulates to keep the engine cool.

Question 23

what is the use of the water pump?

Answer 23

to circulate water through to the water jackets and towards the radiator.

Question 24

what is the use of the radiator?

Answer 24

to contain the water which is supplied to the engine. because of its thin copper tubes and with the aid of the fan, the water which passes through the radiator to the engine is kept cool.

Question 25

what is the use of the fan belt?

Answer 25

it drives the generator, water pump and fan by means of the crankshaft pulley

Question 26

what can cause an engine to get overheated?

Answer 26

Broken or slack fan belt
poor water circulation
lack of water
dirty radiator
retarded ignition
defective water pump
clutch slipping
brakes binding and running for too long in low gears.

Question 27

what are the symptoms of overheating?

Answer 27

pinking
boiling
loss of power

Question 28

why should you flush the radiator occasionally?

Answer 28

to dislodge particles of dirt or grit clogging the tubes that was causing poor circulation of water

Question 29

what is the proper way to replace a fan belt?

Answer 29

1. slacken the generator
2. place belt over the fan and generator pulley wheels
3. hold the belt to the crank shaft pulley
4. with the aid of a crank handle turn the engine for the belt to slip in the pulley grove.
5. adjust generator to get proper tension.