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Published byLynn Kelly Modified over 8 years ago
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Everything a 4 stroke engine does in 2 revolutions a 2 stroke engine does in 1 revolution of the crankshaft 11/2001 2
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3 Piston Cylinder CrankshaftConnecting Rod Still uses a flywheel (not shown) Combustion chamber Intake port Exhaust port Reed valve Transfer port Crankcase
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4 Lets start with the strokes
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11/2001 5 TDC BDC Piston moves from BDC to TDC Air/Fuel/Oil mixture is sucked into crankcase Reed Valve Is sucked open
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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
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7 TDC BDC Piston gets to TDC Air/Fuel/Oil mixture is now trapped in crankcase Reed Valve Shuts
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11/2001 8 TDC BDC Piston moves back To BDC Air/Fuel/Oil mixture is now pressurized in crankcase Reed Valve sealing
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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
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10 Crankcase Compression
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11/2001 12 Cylinder fills with A/F/O mixture
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11/2001 13 Another A/F/O mixture is sucked into crankcase while First one is compressed in cylinder Compression
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11/2001 14 TDC BDC Piston gets to TDC Air/Fuel/Oil mixture is ignited in cylinder Piston is pounded Down the cylinder
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11/2001 15 Crankcase Compression What is going to happen when the piston gets here?
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11/2001 16 TDC BDC Exhaust port is uncovered and exhaust starts leaving Still closed
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11/2001 17 ANOTHER POWER STROKE OK, I get it !
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11/2001 18 Every time the piston reaches TDC, there is another power stroke !
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11/2001 37 Look for two stroke with no reed valve
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Pre-mix ◦ Have to mix before filling tank Oil injection ◦ Has separate fuel and oil tank and carburetor to mix proper amounts 11/2001 39
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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 11/2001 40
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16 to 125 to 132 to 1 40 to 150 to 175 to 1 100 to 1 11/200141 Look in owners manual for exact ratio for your engine
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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 11/2001 42 1 pint = 16 oz 2 pints = 1 qt 1 quart = 32 oz 4 quarts in a gal 32 X 4 = 128 1 gal = 128 oz How am I going to figure this out? Think........ 5 gals X 128 ozs would give me... 640 ozs of fuel 640 ozs of fuel divided by 32.... 128 X 5 640 32 2 64 0 20 oz of oil for 640 oz of fuel or 5 gallons
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16 to 125 to 132 to 1 40 to 150 to 175 to 1 100 to 1 11/200143 Let’s say we are going snowmobiling for the Weekend and you have 1 quart of two stroke oil You figure it out
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11/2001 44 1 pint = 16 oz 2 pints = 1 qt 1 quart = 32 oz 4 quarts in a gal 32 X 4 = 128 1 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 128 11/2001 46 1 pint = 16 oz 2 pints = 1 qt 1 quart = 32 oz 4 quarts in a gal 32 X 4 = 128 1 gal = 128 oz
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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 11/2001 47 Measure, don’t guess!
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11/2001 48 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)
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Two stroke ◦ Exhaust port in center of cylinder ◦ Small crankcase Four stroke ◦ Exhaust port in end of cylinder ◦ Large crankcase 11/2001 49
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Because it is light, can be used at any angle, operates at high RPM ◦ Weed eaters ◦ Chain saws ◦ Boats ◦ Snowmobiles ◦ Dirt bikes 11/2001 50
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Because of pollution, efficiency, lack of low RPM power, and convenience of not mixing oil ◦ Cars ◦ Trucks ◦ Road bikes ◦ Lawn mowers ◦ Generators 11/2001 51
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The crankcase below each piston has to be sealed to create crankcase compression for that cylinder 11/2001 52
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