Dirt ad Trail Online Nov 2020

how a diesel
engine works
HONDA CRF1100 D
2020
0 KM’S
R240 300
HONDA ELITE 125
2020
0 KM’S
R25 900
CUSTOM
HONDA CBR215R
2013
8 400 KM’S
R26 900
A typical inline 4
cylinder engine
HONDA CRF1100 D4
2020
2 900 KM’S
R269 900
HONDA CRF1000
2018
7 900 KM’S
R129 900
BMW F850 GS
2019
5 800 KM’S
R169 900
“squeeze,” “bang” and “blow” strokes as
they are more commonly termed.
1. INTAKE: The stroke of the piston
begins at top dead centre. The piston
descends from the top of the cylinder to
the bottom of the cylinder, increasing the
volume of the cylinder. A mixture of fuel
and air is forced by outside atmospheric
(or greater) pressure into the cylinder
through the intake port.
2. COMPRESSION: With both intake and
exhaust valves closed, the piston returns
to the top of the cylinder compressing
the air or fuel-air mixture into the cylinder
head.
3. POWER: This is the start of the
second revolution of the cycle. While the
piston is close to Top Dead Centre, the
compressed air–fuel mixture in a petrol
engine is ignited, by a spark plug - or
ignites due to the heat generated by
compression in a diesel engine. The
resulting pressure from the combustion
of the compressed fuel-air mixture forces
the piston back down toward bottom
dead centre.
4. EXHAUST: During the exhaust stroke,
the piston once again returns to top dead
centre while the exhaust valve is open.
This action expels the spent fuel-air
mixture through the exhaust valve(s).
Because it can be made to be light,
powerful and compact, the very simple
two stroke engine is a big favourite with
dirt bike manufacturers…
A two-stroke or two-cycle engine is
a type of internal combustion engine
which completes a power cycle in only
one crankshaft revolution and with two
strokes, or up and down movements, of
the piston in comparison to a “four-stroke
engine”, which uses four strokes.
This is accomplished by the end of the
combustion stroke and the beginning
of the compression stroke happening
simultaneously and performing the
intake and exhaust (or scavenging)
functions at the same time. It does not
have a camshaft or valves, and
fuel enters the engine through a
hole, or “port” in one side of the
cylinder wall, and the exhaust
gas blows out another hole
(port) in the opposite cylinder
wall.
As the piston moves up and down it
uncovers these “Ports” in sequence.
This all happens in “two strokes “of
the conrod, one crankshaft rotation.
Once to suck fuel in, compress and
burn it, and the second time to expel
the burned gas through the port into the
exhaust pipe.
Therefore, a 250 two stroke single will
generally generate more power than a
250 four-stroke single.
A two stroke engine also has a dry crank,
where most other engines have cranks
that run in oil baths or sumps. So, how
is the crank shaft lubricated on a two
stroke? Lubrication is derived from the
two stroke oil you mix in with your petrol
which atomises on combustion and the
vapour then provides lubrication to the
crank, also another reason two stroke
engines develop better power more
quickly than a four stroke equivalent. The
oil bath creates drag on the four stroke
crank where the two stroke crank spins
more easily in a cloud of vapour.
The Rotary engine: Not common at all
in the bike industry. A rotary engine, like
the ordinary reciprocating engine (where
the piston goes up and down, both two
and four-strokes) gets its driving power
from the same
compression
HONDA CRF1000
2019
12 000 KM’S
R159 900
HONDA NC750x
2019
3 800 KM’S
R95 000
KAWASAKI ER6N
2016
3 400 KM’S
R64 900
What is a 2-stroke engine?
Single, twin, triple, crank and piston
only no valves or camshafts and rather
use what is commonly referred to as
reed valves in a rad block… usually
found in dirt bikes although quite a few
manufacturers made 2-stroke powered
road bikes.
During each firing stroke, where the
power is generated, a two stroke makes
roughly only 60% of the power a four
stroke makes. However, it has twice as
many power-strokes as a four-stroke.
It has as a better power to weight ratio
but is heavier on fuel as well.
A diesel engine.