How Does A Small Engine Work? 2 & 4 Cycle

Summary

This 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

00:00

🔧 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.

05:03

🔧 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.

10:04

🔧 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.

15:04

🔧 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.

Keywords

💡Four-stroke engine

A four-stroke engine is an internal combustion engine that completes one cycle of operation in four separate strokes of the piston within the cylinder. The strokes are intake, compression, power, and exhaust. In the video, the narrator explains that small engines operate on 'magic', referring to the four different strokes that make the engine run, with a lawnmower engine being used as an example.

💡Crankcase

The crankcase is the lower part of an internal combustion engine in which the crankshaft runs. It houses the engine oil used to lubricate the internal engine parts. The video script distinguishes between four-stroke and two-stroke engines by mentioning that a four-stroke engine has a crankcase for engine oil, unlike a two-stroke engine where oil is mixed with the fuel.

💡Carburetor

A carburetor is a device that mixes air and fuel for internal combustion engines. In the script, the carburetor is described as having a float bowl, which regulates the fuel level, and a nozzle that mixes the fuel with air drawn in by the piston's downward stroke, creating a combustible mixture for the engine.

💡Intake stroke

The intake stroke is the first of the four strokes of a four-stroke engine, during which the piston moves downward, creating a vacuum that draws in a mixture of air and fuel into the combustion chamber. The video uses the character 'Slippers' to illustrate this process, emphasizing the role of the intake valve opening to allow the mixture to enter.

💡Compression stroke

The compression stroke is the second stroke in a four-stroke engine cycle, where the piston moves upward, compressing the air-fuel mixture in the combustion chamber. The video script explains this process with the help of 'Uncle Andy', noting that both the intake and exhaust valves are closed during this stroke.

💡Power stroke

The power stroke is the third stroke in the four-stroke cycle, where the spark plug ignites the compressed air-fuel mixture, causing a mini explosion that pushes the piston downward, providing power to the engine. The video uses 'Skippy' to represent this stroke, highlighting the importance of the spark plug's role in igniting the mixture.

💡Exhaust stroke

The exhaust stroke is the fourth and final stroke in the four-stroke engine cycle, where the piston moves upward again, this time to expel the burnt gases from the combustion chamber through the open exhaust valve. The video script uses 'Anthony' to represent this stroke, describing how the exhaust gases are forced out after the power stroke.

💡Two-stroke engine

A two-stroke engine is a type of internal combustion engine that completes its cycle in only two strokes, as opposed to the four strokes of a four-stroke engine. The video script explains that in a two-stroke engine, oil is mixed with the fuel for lubrication, and the engine operates on a simpler mechanism with different methods of delivering the air-fuel mix to the combustion chamber.

💡Compression release

A compression release is a feature on some engines that slightly relieves compression to make starting the engine easier. The video script describes how the compression release works, with a camshaft lobe that momentarily opens the valve to reduce compression, and a centrifugal force mechanism that disengages the release during normal engine operation.

💡Spark plug

A spark plug is a device that delivers a spark to ignite the compressed air-fuel mixture in the combustion chamber. In the video, the spark plug is crucial during the power stroke, where it ignites the mixture to produce the power that drives the engine. The script mentions a specific type of spark plug, 'J19 LM', used in the demonstration.

💡Four-mix engine

A four-mix engine is a variation of a four-stroke engine that does not have a separate crankcase for engine oil and instead requires the oil to be mixed with the gasoline. The video script briefly touches on this unusual configuration, noting that it operates on the same four-cycle principle but requires a two-cycle oil-mixing practice.

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

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