1. 2 Stoke Engines
Everything a 4 stroke engine does in 2 revolutions a 2 stroke engine does in 1 revolution of the crankshaft
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2. 2 Stroke Engines
The next page in your notebooks will be “2 stroke engines” page #_________
There will be a “2 Stroke Quiz” _______
Lets start with the names of the parts
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3. 2 Stoke Engines part names
Cylinder
Still uses a flywheel
(not shown)
Combustion
chamber
Exhaust port
No Valve Train
Crankcase
Reed valve
Piston
Connecting
Rod
Crankshaft
Intake port
Transfer port
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4. 2 Stroke Engines Turn your page over and lets start with the strokes
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5. Intake/________ Stroke
TDC
BDC
Reed Valve
Is sucked
open
Piston moves from
BDC to TDC
Air/Fuel/Oil mixture is sucked into crankcase
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6. Compare intake strokes
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
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7. Down to bottom of page Reed Valve TDC BDC Shuts Piston gets to TDC
Air/Fuel/Oil mixture is now trapped in crankcase
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8. Crankcase compression (primary compression)
TDC
Reed Valve
sealing
BDC
Piston moves back
To BDC
Air/Fuel/Oil mixture is now pressurized in crankcase
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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
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10. What is going to happen when the top of piston gets to here?
Crankcase
Compression
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11. A/F/O mixture squirts into cylinder because of crankcase compression
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12. Piston reaches BDC
Cylinder fills with
A/F/O mixture
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13. Intake/________ Stroke
Compression
Another A/F/O mixture is sucked into crankcase while
First one is compressed in cylinder
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14. Down to bottom of page TDC BDC Piston is pounded Down the cylinder
Piston gets to
TDC
Air/Fuel/Oil mixture is ignited in cylinder
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15. Blow-by adds to crankcase compression
What is going to happen when the piston gets here?
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16. Power/Exhaust Stroke (TDC-BDC)
Still closed
Exhaust port is uncovered and exhaust starts leaving
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17. What’s going to happen when the piston gets back to TDC
OK, I get it !
ANOTHER POWER STROKE
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18. Every time the piston reaches TDC, there is another power stroke !
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19. Let’s make a chart
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20. Let’s make a chart
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21. Let’s make a chart
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22. Let’s make a chart
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23. Let’s make a chart
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24. Let’s make a chart
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25. Reed valve on the side of crankcase
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30. Tuned Exhaust
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31. Tuned Exhaust
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33. Tuned Exhaust
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34. Power stroke every revolution
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35. Oil mixing Pre-mix Oil injection Have to mix before filling tank
Has separate fuel and oil tank and carburetor to mix proper amounts
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36. Advantages 2 Stroke 4 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
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37. 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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38. 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)
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39. 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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40. 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
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41. Usually don’t see 2 strokes in
Because of pollution, efficiency, lack of low RPM power, and convenience of not mixing oil
Cars
Trucks
Road bikes
Lawn mowers
Generators
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42. Multiple cylinder two strokes
The crankcase below each piston has to be sealed to create crankcase compression for that cylinder
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