 Everything a 4 stroke engine does in 2 revolutions a 2 stroke engine does in 1 revolution of the crankshaft 11/2001 2

3 Piston Cylinder CrankshaftConnecting Rod Still uses a flywheel (not shown) Combustion chamber Intake port Exhaust port Reed valve Transfer port Crankcase

4 Lets start with the strokes

11/ TDC BDC Piston moves from BDC to TDC Air/Fuel/Oil mixture is sucked into crankcase Reed Valve Is sucked open

 Two Stroke ◦ Piston BDC to TDC ◦ A/F/O mixture sucked into crankcase  Four Stroke ◦ Piston TDC to BDC ◦ A/F mixture sucked into cylinder 11/2001 6

7 TDC BDC Piston gets to TDC Air/Fuel/Oil mixture is now trapped in crankcase Reed Valve Shuts

11/ TDC BDC Piston moves back To BDC Air/Fuel/Oil mixture is now pressurized in crankcase Reed Valve sealing

 Is only a few pounds of pressure per square inch (psi) [very weak]  Cylinder compression in a four stroke engine was several psi [very strong]  The crankcase in a two stroke engine has to be very small so we can build some pressure when the piston is moving to BDC 11/2001 9

10 Crankcase Compression

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11/ Cylinder fills with A/F/O mixture

11/ Another A/F/O mixture is sucked into crankcase while First one is compressed in cylinder Compression

11/ TDC BDC Piston gets to TDC Air/Fuel/Oil mixture is ignited in cylinder Piston is pounded Down the cylinder

11/ Crankcase Compression What is going to happen when the piston gets here?

11/ TDC BDC Exhaust port is uncovered and exhaust starts leaving Still closed

11/ ANOTHER POWER STROKE OK, I get it !

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

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11/ Look for two stroke with no reed valve

 Pre-mix ◦ Have to mix before filling tank  Oil injection ◦ Has separate fuel and oil tank and carburetor to mix proper amounts 11/

 2 Stroke ◦ Smaller/lighter ◦ Cheaper ◦ Less friction ◦ No oil to change ◦ Quicker acceleration ◦ Operate at different angles  4 Stroke ◦ More efficient ◦ No oil to mix ◦ Less emissions ◦ Less exhaust smoke ◦ More low RPM power 11/

16 to 125 to 132 to 1 40 to 150 to 175 to to 1 11/ Look in owners manual for exact ratio for your engine

 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 11/ pint = 16 oz 2 pints = 1 qt 1 quart = 32 oz 4 quarts in a gal 32 X 4 = gal = 128 oz How am I going to figure this out? Think gals X 128 ozs would give me ozs of fuel 640 ozs of fuel divided by X oz of oil for 640 oz of fuel or 5 gallons

16 to 125 to 132 to 1 40 to 150 to 175 to to 1 11/ Let’s say we are going snowmobiling for the Weekend and you have 1 quart of two stroke oil You figure it out

11/ pint = 16 oz 2 pints = 1 qt 1 quart = 32 oz 4 quarts in a gal 32 X 4 = gal = 128 oz

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 32 oz times 50 = 1600  I will need 1600 oz of fuel for 32 oz of oil with a 50 to 1 ratio  Since there are 128 oz in a gallon, divide 1600 by / pint = 16 oz 2 pints = 1 qt 1 quart = 32 oz 4 quarts in a gal 32 X 4 = gal = 128 oz

 If you forget to add oil for one tank of gas, you will destroy your engine  If you mix too much oil with the gas ◦ Your 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 don’t mix enough oil with the gas ◦ You will cause lots of engine wear 11/ Measure, don’t guess!

11/ Notice 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)

 Two stroke ◦ Exhaust port in center of cylinder ◦ Small crankcase  Four stroke ◦ Exhaust port in end of cylinder ◦ Large crankcase 11/

 Because it is light, can be used at any angle, operates at high RPM ◦ Weed eaters ◦ Chain saws ◦ Boats ◦ Snowmobiles ◦ Dirt bikes 11/

 Because of pollution, efficiency, lack of low RPM power, and convenience of not mixing oil ◦ Cars ◦ Trucks ◦ Road bikes ◦ Lawn mowers ◦ Generators 11/

 The crankcase below each piston has to be sealed to create crankcase compression for that cylinder 11/