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Two Stroke Engines

Two Stroke Engines

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Two Stroke Engines

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  1. Two Stroke Engines

  2. 2 Stoke Engines • Everything a 4 stroke engine does in 2 revolutions a 2 stroke engine does in 1 revolution of the crankshaft

  3. 2 Stoke Engines part names Still uses a flywheel (not shown) Cylinder Combustion chamber Exhaust port Crankcase Reed valve Piston Connecting Rod Crankshaft Intake port Transfer port

  4. 2 Stroke Engines Lets start with the strokes

  5. TDC BDC Reed Valve Is sucked open Intake Stroke Piston moves from BDC to TDC Air/Fuel/Oil mixture is sucked into crankcase

  6. Compare intake strokes • Four Stroke • Piston TDC to BDC • A/F mixture sucked into cylinder • Two Stroke • Piston BDC to TDC • A/F/O mixture sucked into crankcase

  7. TDC BDC Reed Valve Shuts Down to bottom of page Piston gets to TDC Air/Fuel/Oil mixture is now trapped in crankcase

  8. TDC BDC Reed Valve sealing Crankcase compression (primary compression) Piston moves back To BDC Air/Fuel/Oil mixture is now pressurized in crankcase

  9. Crankcase compression • 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

  10. Crankcase Compression What is going to happen when the top of piston gets to here?

  11. A/F/O mixture squirts into cylinder because of crankcase compression

  12. Piston reaches BDC Cylinder fills with A/F/O mixture

  13. Intake/________ Stroke Compression Another A/F/O mixture is sucked into crankcase while First one is compressed in cylinder

  14. TDC BDC Down to bottom of page Piston is pounded Down the cylinder Piston gets to TDC Air/Fuel/Oil mixture is ignited in cylinder

  15. Crankcase Compression Blow-by adds to crankcase compression What is going to happen when the piston gets here?

  16. TDC BDC Power/Exhaust Stroke (TDC-BDC) Still closed Exhaust port is uncovered and exhaust starts leaving

  17. What’s going to happen when the piston gets back to TDC OK, I get it ! ANOTHER POWER STROKE

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

  19. Let’s make a chart

  20. Let’s make a chart

  21. Let’s make a chart

  22. Let’s make a chart

  23. Let’s make a chart

  24. Let’s make a chart

  25. Let’s make a chart

  26. Let’s make a chart Will be on Quiz

  27. Reed valve on the side of crankcase

  28. Tuned Exhaust

  29. Tuned Exhaust

  30. Tuned Exhaust

  31. Tuned Exhaust

  32. Power stroke every revolution

  33. Let’s watch CDX Disk 4-1 Look for two stroke with no reed valve

  34. Oil mixing • Pre-mix • Have to mix before filling tank • Oil injection • Has separate fuel and oil tank and carburetor to mix proper amounts

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

  36. Fuel to Oil mixtures Look in owners manual for exact ratio for your engine

  37. 32 to 1 Mix How am I going to figure this out? Think . . Think . . Think . . Think . . Think 5 gals X 128 ozs would give me . . . 640 ozs of fuel 640 ozs of fuel divided by 32 . . . . 20 oz of oil for 640 oz of fuel or 5 gallons • 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 qt 1 quart = 32 oz 4 quarts in a gal 32 X 4 = 128 1 gal = 128 oz 2 0 128 32 640 X 5 64 640

  38. Fuel to Oil mixtures You figure it out Let’s say we are going snowmobiling for the Weekend and you have 1 quart of two stroke oil

  39. How many gallons of fuel will be needed to mix with one quart of oil with a 50 to 1 ratio 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

  40. There is always more than one way to figure something out

  41. 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 ratio • Since there are 128 oz in a gallon, divide 1600 by 128 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 12.5 Gallons

  42. Mixing oil is critical • 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 Measure, don’t guess!

  43. Two stroke piston 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)

  44. How to identify from outside • Four stroke • Exhaust port in end of cylinder • Large crankcase • Two stroke • Exhaust port in center of cylinder • Small crankcase

  45. Good uses of two stroke engines • Because it is light, can be used at any angle, operates at high RPM • Weed eaters • Chain saws • Boats • Snowmobiles • Dirt bikes