Two Stroke Engines.ppt

8/14/2019 Two Stroke Engines.ppt

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Two Stroke Engines

Will need CDX Disk 4-1 on day 2


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2 Stoke Engines

Everything a 4 strokeengine does in 2

revolutions a 2 strokeengine does in 1revolution of the

crankshaft


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2 Stroke Engines

The next page in your notebooks will be2 stroke engines page #_________

There will be a 2 Stroke Quiz _______Lets start with the names of the parts


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2 Stoke Engines part names

Piston

Cylinder

CrankshaftConnectingRod

Still uses a flywheel(not shown)Combustion

chamber

Intake port

Exhaust port

Reed valve

Transfer port

Crankcase


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2 Stroke Engines

Turn your page over and lets start with the strokes


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Intake/________ Stroke

TDC BDC

Piston moves fromBDC to TDC

Air/Fuel/Oil mixture is sucked into crankcase

Reed ValveIs sucked

open


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Two Stroke

Piston BDC to TDC

A/F/Omixturesucked intocrankcase

Four Stroke

Piston TDC to BDC

A/F mixture suckedinto cylinder

Compare intake strokes


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Down to bottom of page

TDC BDC

Piston gets toTDC

Air/Fuel/Oil mixture is now trapped in crankcase

Reed ValveShuts


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Crankcase compression (primary compression)

TDC BDC

Piston moves backTo BDC

Air/Fuel/Oil mixture is now pressurized in crankcase

Reed Valvesealing


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Crankcase compression

Is only a few pounds of pressure persquare inch (psi) [very weak]

Cylinder compression in a four strokeengine was several psi [very strong]

The crankcase in a two stroke enginehas to be very small so we can buildsome pressure when the piston ismoving to BDC


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CrankcaseCompression

What is going to happen whenthe top of piston gets to here?


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A/F/O mixture squirts intocylinder because of crankcase compression


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Piston reaches BDC

Cylinder fills withA/F/O mixture


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Intake/________ Stroke

AnotherA/F/O mixture is sucked into crankcase while

First one is compressed in cylinder

Compression


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Down to bottom of page

TDC BDC

Piston gets toTDC

Air/Fuel/Oil mixture is ignited in cylinder

Piston is poundedDown the cylinder


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Blow-by adds to crankcasecompression

CrankcaseCompression

What is going to happen when the piston gets here?


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Power/Exhaust Stroke (TDC-BDC)

TDC BDC

Exhaust port is uncovered and exhaust starts leaving

Still closed


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Whats going to happen whenthe piston gets back to TDC

ANOTHER POWER

STROKE

OK, I get it


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Every time the piston reaches TDC,there is another power stroke


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Lets make a chart

Stroke Piston A/F/O Mixture

Intake/Compression BTC-TDC Sucked into crankcase, another squeezed in cylinder

Power/Exhaust TDC-BDC Blows-up and leaves, another squeezed in crankcase


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Lets make a chart





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Lets make a chart





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Lets make a chart





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Lets make a chart





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Lets make a chart





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Lets make a chart





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Lets make a chart





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Reed valve on the side of crankcase


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Tuned Exhaust


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Tuned Exhaust


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Power stroke every revolution


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Lets watch CDX Disk 4-1

Look for two stroke with no reed valve


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Oil mixing

Pre-mix Have to mix before

filling tank

Oil injection Has separate fuel

and oil tank andcarburetor to mixproper amounts


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Advantages

2 Stroke

Smaller/lighter

Cheaper

Less friction

No oil to change

Quicker acceleration

Operate at differentangles

4 Stroke

More efficient

No oil to mix

Less emissions

Less exhaust smoke

More low RPM power


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Fuel to Oil mixtures

16 to 1 25 to 1 32 to 1

40 to 1 50 to 1 75 to 1

100 to 1

Look in owners manual for exact ratio for your engine


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32 to 1 Mix

32 parts of gasoline to 1 part of oil

32 ounces of gas to 1 ounce of oil

32 pints of gas to 1 pint of oil

32 quarts of gas to 1 quart of oil

5 gallon gas can = How many ounces of oil

1 pint = 16 oz

2 pints = 1 qt1 quart = 32 oz4 quarts in a gal

32 X 4 = 1281 gal = 128 oz

How am I going to figurethis out?

Think . . Think . . Think . .Think . . Think

5 gals X 128 ozs would giveme . . . 640 ozs of fuel

640 ozs of fuel divided by 32. . . .

128X 5

640

640322

64

0

20 oz of oil for 640 oz offuel or 5 gallons


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Fuel to Oil mixtures

16 to 1 25 to 1 32 to 1

40 to 1 50 to 1 75 to 1

100 to 1Lets say we are going snowmobiling for theWeekend and you have 1 quart of two stroke oil

You figure it out


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How many gallons of fuel willbe needed to mix with one

quart of oil with a 50 to 1 ratio1 pint = 16 oz2 pints = 1 qt

1 quart = 32 oz4 quarts in a gal

32 X 4 = 1281 gal = 128 oz


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There is always more thanone way to figure something

out


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Here is how I figured it out

32 oz times 50 = 1600

I will need 1600 oz of fuel for 32 oz of

oil with a 50 to 1 ratioSince there are 128 oz in a gallon,divide 1600 by 128

1 pint = 16 oz

2 pints = 1 qt1 quart = 32 oz4 quarts in a gal

32 X 4 = 1281 gal = 128 oz


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Mixing oil is critical

If you forget to add oil for one tank ofgas, you will destroy your engine

If you mix too much oil with the gasYour engine will smoke a lot It will be hard to start

It will have less power

It might foul the spark plug (not start)If you dont mix enough oil with the gasYou will cause lots of engine wear


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Two stroke pistonNotice the piston skirt scars

(lack of oil)

Notice the 2 ring lands(only have compression rings)

Notice the ring pins(prevents rings from rotating

And catching on cylinder ports)


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How to identify from outside

Two stroke Exhaust port in

center of cylinder

Small crankcase

Four stroke Exhaust port in end

of cylinder

Large crankcase


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Good uses of two stroke engines

Because it is light, can be used at anyangle, operates at high RPM

Weed eaters Chain saws

Boats

Snowmobiles Dirt bikes


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Two stroke engine questions?

Two Stroke Engines.ppt

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