How Does A Small Engine Work? 2 & 4 Cycle
Summary
TLDRThis video script provides an educational overview of small engine mechanics, focusing on the differences between two-stroke and four-stroke engines. It explains the four-stroke cycle, which includes intake, compression, power, and exhaust, using a lawnmower engine as an example. The script also touches on the two-stroke engine, which combines the intake and compression strokes and uses a mixture of oil and gas for lubrication. The presenter humorously introduces 'four-mix' engines, which are four-stroke engines that require oil mixed with gas, and encourages viewers to subscribe and engage with the content for more insights.
Takeaways
- 🔧 The script explains the workings of small engines, specifically focusing on four-stroke and two-stroke engines.
- 🌀 A four-stroke engine completes one cycle through four distinct strokes: intake, compression, power, and exhaust.
- 💧 In a four-stroke engine, the intake stroke involves drawing a fuel-air mixture into the combustion chamber as the piston moves downward.
- 🔥 The compression stroke sees the piston compressing the fuel-air mixture in the combustion chamber, preparing it for ignition.
- ⚙️ The power stroke occurs when the spark plug ignites the compressed fuel-air mixture, causing an explosion that drives the piston downward.
- 🌬️ The exhaust stroke expels the burnt gases from the combustion chamber as the piston moves upward and the exhaust valve opens.
- 🛠️ A key difference between four-stroke and two-stroke engines is the presence of a crankcase for engine oil in four-stroke engines, versus a combined oil-gas mixture in two-stroke engines.
- 🚫 Two-stroke engines do not have a separate crankcase for engine oil; instead, oil is mixed with the fuel for lubrication.
- 🔄 The script humorously suggests that small engines 'run on magic,' highlighting the complexity of their operation.
- 🛑 The script also touches on 'four-mix' engines, which are four-stroke engines that require oil mixed with the fuel, similar to two-stroke engines.
- 👨🏫 The educational nature of the script is intended to clarify the differences between engine types and their operational cycles.
Q & A
What is the difference between a four-stroke and a two-stroke engine?
-A four-stroke engine completes one cycle through four separate strokes: intake, compression, power, and exhaust. It has a separate crankcase for engine oil. A two-stroke engine completes its cycle in only two strokes: the intake and compression occur simultaneously, followed by combustion and exhaust in the second stroke. It mixes oil with the fuel for lubrication, as it doesn't have a separate crankcase for engine oil.
What are the four strokes of a four-stroke engine?
-The four strokes of a four-stroke engine are intake, compression, power, and exhaust. During the intake stroke, the air-fuel mixture is drawn into the combustion chamber. The compression stroke compresses the mixture, the power stroke ignites the mixture causing the piston to move, and the exhaust stroke expels the burnt gases.
How does the carburetor play a role in the intake stroke of a four-stroke engine?
-The carburetor mixes air and fuel before the intake stroke. As the piston moves downward, it draws air across the carburetor, pulling fuel from the float bowl through the center nozzle. The air and fuel mix is then carried into the combustion chamber through the intake manifold as the intake valve opens.
What is the purpose of the compression release on some engines?
-The compression release is used to relieve some of the compression in the engine to make it easier to start. It works by momentarily bumping the valve open during the compression stroke, reducing the pressure. When the engine is running, centrifugal force keeps the compression release disengaged to prevent continuous bumping.
How does the spark plug contribute to the power stroke in a four-stroke engine?
-The spark plug ignites the compressed air-fuel mixture in the combustion chamber during the power stroke. This ignition causes a small explosion that pushes the piston downward, providing power to the engine.
What is the role of the exhaust valve in the exhaust stroke of a four-stroke engine?
-The exhaust valve opens during the exhaust stroke to expel the burnt gases from the combustion chamber. The piston moves upward, pushing the exhaust gases out through the open exhaust valve.
Why is it necessary to mix oil with gasoline in a two-stroke engine?
-In a two-stroke engine, oil is mixed with gasoline to provide lubrication since there is no separate crankcase for engine oil. Without oil mixed in the fuel, the engine would lack lubrication and could be damaged.
What are the two strokes of a two-stroke engine?
-The two strokes of a two-stroke engine are the intake and compression stroke followed by the combustion and exhaust stroke. The air-fuel mixture is drawn in and compressed in the first stroke, and then ignited and expelled in the second stroke.
What is a four-mix engine and how does it differ from a typical four-stroke engine?
-A four-mix engine is a four-stroke engine that does not have a separate crankcase for engine oil. Instead, it requires oil to be mixed with the gasoline, similar to a two-stroke engine, for lubrication.
What are some variations in how two-stroke engines deliver the air-fuel mix to the combustion chamber?
-Two-stroke engines can use a reed valve or piston porting to deliver the air-fuel mix to the combustion chamber. Some engines may also have a wedge on the piston to help deflect exhaust gases out during the exhaust stroke.
Outlines
🔧 Introduction to Four-Stroke Engines
The script introduces the concept of a four-stroke engine, also known as a four-cycle engine, which operates through four distinct cycles or strokes. The presenter uses humor to explain that small engines 'run on magic', referring to the four strokes. A lawnmower engine is used as an example. The difference between four-stroke and two-stroke engines is highlighted, with the former having a crank case for engine oil and the latter mixing oil with gas for lubrication. The first stroke, intake, is explained in detail, showing how air and fuel mix in the carburetor, drawn into the combustion chamber by the piston's downward movement, with the intake valve opening and the exhaust valve closing at the right time, controlled by the camshaft.
🔧 The Compression and Power Strokes
The second stroke, compression, is detailed, where the piston rises, compressing the fuel-air mixture in the combustion chamber with both valves closed. The script humorously uses a character to personify the compression stroke. The third stroke, power, is where the spark plug ignites the compressed mixture, causing an explosion that pushes the piston down. The fourth and final stroke, exhaust, is also explained, where the piston rises again, pushing the exhaust gases out through the open exhaust valve. The script uses a character to represent the exhaust stroke, emphasizing the release of 'stinky gases'. The entire process is cyclical, with the engine starting over after the exhaust stroke.
🔧 Two-Stroke Engines and Their Lubrication
The script contrasts two-stroke engines with four-stroke engines, emphasizing that two-stroke engines require oil mixed with gas for lubrication due to the lack of a separate crankcase for engine oil. The presenter explains the necessity of oil mixing to prevent engine damage. Different methods of air-fuel mixture delivery in two-stroke engines are discussed, such as reed valves and piston ports. The script also touches on variations like engines with a wedge on the piston to help direct exhaust gases out. The two strokes of a two-stroke engine—intake and compression followed by combustion, and exhaust—are summarized, highlighting the simplicity of their operation compared to four-stroke engines.
🔧 The Unique Case of Four-Mix Engines
The script concludes with a discussion on four-mix engines, a type of four-stroke engine that also requires oil mixed with gas, despite having a crankcase for engine oil. This is presented as a 'wacky' concept, differentiating it from typical four-stroke engines. The presenter humorously addresses the potential confusion among viewers and provides a light-hearted approach to engine repair, suggesting that sometimes fixing engines involves trial and error. The script ends with a call to action for viewers to subscribe to the YouTube channel, follow on social media, and visit the web store for merchandise.
Mindmap
Keywords
💡Four-stroke engine
💡Crankcase
💡Carburetor
💡Intake stroke
💡Compression stroke
💡Power stroke
💡Exhaust stroke
💡Two-stroke engine
💡Compression release
💡Spark plug
💡Four-mix engine
Highlights
Introduction to the four-stroke engine and its operation.
Explanation of the difference between four-stroke and two-stroke engines.
Description of the crankcase's role in a four-stroke engine for oil lubrication.
Illustration of the intake stroke with a lawnmower engine example.
Detailed explanation of how the carburetor mixes air and fuel.
Demonstration of the piston's movement during the intake stroke.
Compression stroke explained with a focus on valve operation.
Visual aid showing the piston's compression of the air-fuel mixture.
Discussion on the purpose of a compression release mechanism.
Power stroke described, highlighting the role of the spark plug.
Exhaust stroke explained, focusing on the expulsion of combustion byproducts.
Overview of the four-stroke cycle and its continuous nature.
Introduction to the two-stroke engine and its simplified operation.
Necessity of mixing oil with gasoline in a two-stroke engine for lubrication.
Different methods of air-fuel mixture delivery in two-stroke engines.
Explanation of the piston port and reed valve systems in two-stroke engines.
Concept of the four-mix engine, a four-cycle engine requiring oil mixed with gas.
Practical advice on engine repair and maintenance.
Encouragement to subscribe to the YouTube channel for more content.
Transcripts
pterodactyl here and today we're going
to go over how a small
engine works how it actually operates in
order to get it to run
now you may have heard of a four stroke
or
four cycle engine it's the same thing
four stroke four cycle it's the same
thing
an engine has to go through four
different
cycles or four different strokes in
order for it to run
but these small engines they actually
run on magic
that's how they run on magic they run on
four different strokes
so to illustrate this we have a small
lawnmower engine it's a four stroke
engine
the typical way to tell a four-stroke
engine from say a two-stroke engine is a
four-stroke engine has a crank case
for the engine oil to lubricate the
internal engine parts
a two-stroke engine the gas
and the oil are mixed and that's how it
gets its lubrication
and that engine goes through two strokes
and we're gonna illustrate that later
but first we're gonna go over the
four-stroke engine
so to illustrate this i brought in four
strokes and our first stroke
is intake which will be illustrated by
slippers
what's up i got to be intake this is
pretty awesome
alright so here's what it says air is
mixed with fuel in the carburetor
and the mixture is drawn into the
combustion chamber by the downward
movement of the piston
the intake valve is open to allow the
fuel air mixture to enter the combustion
chamber the intake valve is open at the
proper time by the lobe on the camshaft
which is geared to the crankshaft the
exhaust valve is closed
so what does that mean exactly all right
so to illustrate that a little better
we're going to show you on this engine
here so as he stated that the book said
air is mixed with fuel in the carburetor
now you're probably wondering how does
that work
so here's the carburetor right here this
is a float bowl
carbotrader now i have a loose
carburetor in my hand
here's the float bowl that we take off
and here's the float
the float's got a needle on it and that
regulates the fuel that comes into the
carburetor because here's the fuel line
coming in
and then the gas runs in to fill up the
bowl
and then when the bowl gets full it
shuts off the gas now as it's using gas
it opens it a little bit to let more in
now that gas
is drawn up through the center of the
carburetor here
there's the nozzle that goes through the
center
so as it stated in the book as the air
is being drawn in
from the piston in its downward stroke
it's pulling the air in across here
which pulls the fuel out of the
float bowl through the center nozzle and
that air and gas gets
mixed and then it's being carried into
the combustion chamber
and on this engine the air and fuel mix
is being carried through this manifold
tube
which in this engine is right above the
intake valve
so as we rotate the engine here here's
the
fins see how the fins are curved for
that way
as we rotate it it's pulled the piston
is going down
which is drawing the air in
mixing that gas and air mix
pulling it through here and as the
intake valve opens
that mix is now
focused right here in the combustion
chamber
this is the combustion chamber we have
the head off
this area here see how that is and
there's the spark plug
so that's our first stroke air gas
coming in
piston going down intake valve is
opening
it's depositing the air and gas mix
in the combustion chamber and then now
we go to our second stroke
our next stroke is compression
which is being played by uncle andy
hey how's it going sometimes i feel like
i'm being compressed
all right what does this say here
compression
as the piston reaches bottom dead
center the intake valve closes
the piston then rises compressing the
fuel
and air mixture trapped in the
combustion
chamber because both valves are closed
i have no idea what i just read
okay so now our piston is traveling down
and when it does that it's you know it's
sucking in the air
while it's doing that and just like
andy said the intake valve is closed
when we're at bottom dead center
now the piston is traveling back up
both valves are closed and in this case
you're going to see this exhaust valve
bump a little bit because this one's got
a compression release on it
see it a little movement
[Music]
that's to relieve some of the
compression to make it start easier
and then now this has compressed
that air fuel mixture at the very top
[Music]
now if you don't know what a compression
release is
i've explained it in many other videos
but here's a camshaft
that has a typical compression release
on it
and here's the lobes that open and close
the valves
now this is all precisely timed to do
this
and this is a compression release so how
this works is
as this is the cam is turning
if you notice this part here on the
compression release
is sticking up above the lobe
so the tap it is riding on there
and it bumps the valve for a split
second just to relieve a little
compression to make it start easier
then when the engine starts centrifugal
force
will swing this weight out of the way
so that way as the engine's running it's
not
bumping that compression release the
whole time
and then when the engine stops
that lever returns to its normal
position so when you go to start it
again it'll bump the compression release
so that's how a compression release
works on
engines that have compression releases
not all of them have a compression
release
our next stroke is power and to play the
part of that
stroke is skippy hey
this is my favorite one it's got spot
plugs involved
all right as the piston reaches the
before top
dead center bt dc
ignition point the spot plug fires
igniting the fuel air mixture in the
time it takes to ignite all the
available fuel
the piston has moved to tdc tap deadset
ready to take the full combustive force
of the fuel for maximum power and piston
downward trap
the expanding gases force the piston
down
both valves remain closed
as skippy explained as the piston is
traveling up
both valves closed just before
top dead center the spark plug will
spark
what kind of spark plug is that dear oh
uh a j19 lm
looking a little rusty
[Music]
so as the spark plug ignites all those
gases that are compressed here in the
combustion chamber
it sets off like a small explosion
because of that gas and air mix
and that happens just as it's reaching
top dead center
and it's starting to travel back down
so when that mixture ignites
that little explosion helps to push the
piston back down
so that's our third stroke power you
understand that now as the pistons
coming up
the ignit the coil sparks the plug
setting off that small explosion
and this all happens in a split second
as this is traveling up
and then just as it's starting to go
back down
that explosion forces the piston back
down
and again both valves are closed
for our fourth and final stroke exhaust
will be played by anthony yeah i see
what you're doing here terrell i don't
really like it
exhaust what are you saying i admit
stinky gasses
or something no no no no we were gonna
we were gonna use elk skins because he's
emitting stinky gases all throughout the
day it's just that he was busy today
and you happen to be in the neighborhood
so we just thought maybe you could do
this for us real quick
yeah all right so anyway exhaust there
we go with the emitting gases
i think you ought to be the exhaust so
anyway as the piston
starts to the top of the cylinder the
exhaust gasses are forced out the open
exhaust valve
after the piston reaches top dead center
tdc
the four cycle process will begin again
as the piston moves downward
and the intake valve opens whatever that
means you
do what you do explaining that there
now we've just had our explosion in the
combustion chamber which is pushing the
piston down
the pistons at the bottom dead
center and as you can see the exhaust is
opening
as the piston is coming back up it's
pushing the exhaust fumes that were
in the combustion chamber and in the
piston chamber here
it's pushing them out the exhaust
and then as soon as it gets to the top
it closes and now as we turn the fist
the crankshaft and the piston starts to
go down
we start to process all over again
you got that so let's do it
now we're at top dead center
both valves are closed we start with our
intake
pistons going down drawing in that gas
and air mixture
through the manifold taking that
mixture depositing it in the combustion
chamber
pistons starting to come up compression
stroke
boom spark plug fires ignites the
the mixture pushes the piston back down
exhaust opens pistons coming up
taking all those gases pushing them out
the muffin
and then again down again pulling in the
mixture
closing the valves compression
ignition igniting it
the explosion pushes the piston back
down opens the exhaust valve
and pushes the stinky exhaust gasses out
those are the four strokes of a four
stroke engine
as illustrated by our four strokes
now i gotta find two more strokes so we
can do a two-stroke engine
i couldn't find two strokes to explain a
two-stroke engine so i'm just gonna do
it myself
now the first thing you need to know
about a two-stroke engine is you have to
mix
oil with the gas it doesn't have a
separate crank case
like a four-stroke engine where you have
engine oil
and then you have a separate gas tank
where you put just regular straight gas
on a two-stroke engine it gets its
lubrication from the oil that you mix
with the gas if you don't mix any oil
with the gas you'll burn this engine up
because it won't get any
kind of lubrication now there's some
different variations on how you get that
air fuel mix to the compression chamber
to ignite it and we're going to show you
those in this manual
that's the only different it still works
on two cycles or two different strokes
there's just a different way of
delivering the air fuel mix
some use a reed valve some are piston
port
you know this is an example of a piston
port
where the carburetor is mounted right
here i didn't have a reed valve
one to show you but the reed valve is
usually at the end of the
end of the crank case and the little
valve little flapper valves are what let
in the
air fuel mix and then there's just
different
porting that deliver
the air fuel mix to the combustion
chamber
and exhausted
some have funny pistons with a like a
wedge on it
that helped kind of deflect the exhaust
gases out on the second stroke
but these are different variations of
two stroke engines and how they get
that air gasoline mix
to the combustion chamber so it just
works on two
two you know simple strokes you have
your intake
your compression and then your uh
uh combustion where the spark it when it
sparks so you got your air intake
it compresses it and then it sparks
your combustion and then your second
stroke
is the uh exhausting of that
exhaust gases after you lit that that
air fuel mix
so that's it just two strokes up and
down
that's why it's called a two stroke now
i know what some of you are thinking
carol carol you need to talk about
stills
4 mix engine how come you didn't talk
about a 4 mix engine
that's right i i can hear you i can hear
you through the screen
there is still had an engine or even
still does
called a four mix and what that is
that's a four-stroke engine
that doesn't have a crankcase for
separate oil you have to mix
oil and gas isn't that weird isn't that
a wacky
concept those guys that still came up
with a
four mix engine it's a four cycle engine
but you have to run two cycle mixing boy
that's probably really making your head
explode right now
and it's the same thing it's just a
four-cycle engine it's got valves and a
cam
shaft and everything and it works the
same way as a four-stroke you know
drone intake compression ignition
exhaust
except it doesn't have a crankcase for
separate engine oil
it gets its lubrication from the oil
that you add to the gasoline
terrell that's all fine and good but how
do i know if i got one of these
four mix engines cause it'll stay on
there for
mix see how these people these smart
people
are confusing us dumb people all the
time with all their
fancy schmancy high technological stuff
well i hope this helped in explaining
the difference between a two cycle and a
four-cycle engine
i hope you learned something today but
you'll probably never use this
information because
what do you need that for if you're
fixing this stuff just fix it
you don't know what's wrong with it just
start changing parts until you hit the
one part that makes it run again
no i'm joking i'm joking
subscribe to this youtube channel tarot
fixes all
that's me terrible follow me
on facebook and instagram with your two
cycle and four cycle engines
go to our web store buy some tarot
apparel and some tarot stuff
and as always there's your dinner
two cycle four cycle explains
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