Mechanics Flashcards
name the strokes of a 4 stroke engine
- induction
- compression
- power also called the explosion or combustion
- exhaust
what happens on the induction stroke?
intake valve open
exhaust valve closed
the piston descending
lastly a mixture of petrol and air is drawn in the cylinder
what happens on compression stroke?
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.
what happens on power stroke?
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.
what happens on the exhaust stroke?
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.
what is the use of the crankshaft?
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.
what is the use of the camshaft?
it operates the valves and
drive the mechanical fuel pump, oil pump, and the distributor shaft
how is the valve opened and closed?
the camshaft opens the valve and
the pressure of the valve spring closes it.
what is the use of the piston?
to transmit power to the engine
what is the use of the connecting rod?
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
what is the use of the fly wheel?
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.
what operates the piston ?
the internal combustion of the engine with
the aid of the continuous momentum of the fly wheel and crankshaft.
name the two types of valves in the engine
intake valve
exhaust valve
how many valves are there in a four cylinder engine?
2x4
8 valves
what is the combustion chamber?
it is the space between the piston and cylinder head
when the piston reaches the end of its stroke “top dead centre”
what is the use of the ring gear?
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.
firing order
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
how many types of piston rings are there and
what are their uses?
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.
what is the main difference between a gas and a diesel engine?
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.
what is an internal combustion engine?
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.
what is the use of the fan?
to assist in sucking air through to the radiator for cooling the engine.
what are water jackets?
they are spaces around the cylinders through which the water circulates to keep the engine cool.
what is the use of the water pump?
to circulate water through to the water jackets and towards the radiator.
what is the use of the radiator?
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.
what is the use of the fan belt?
it drives the generator, water pump and fan by means of the crankshaft pulley
what can cause an engine to get overheated?
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.
what are the symptoms of overheating?
pinking
boiling
loss of power
why should you flush the radiator occasionally?
to dislodge particles of dirt or grit clogging the tubes that was causing poor circulation of water
what is the proper way to replace a fan belt?
- slacken the generator
- place belt over the fan and generator pulley wheels
- hold the belt to the crank shaft pulley
- with the aid of a crank handle turn the engine for the belt to slip in the pulley grove.
- adjust generator to get proper tension.
