1. Two Stroke Engines
Will need CDX Disk 4-1 on day 2

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

3. 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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4. 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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5. 2 Stroke Engines Turn your page over and lets start with the strokes
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6. 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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7. 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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8. 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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9. 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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10. 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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11. What is going to happen when the top of piston gets to here?
Crankcase
Compression
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12. A/F/O mixture squirts into cylinder because of crankcase compression
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13. Piston reaches BDC
Cylinder fills with
A/F/O mixture
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14. Intake/________ Stroke
Compression
Another A/F/O mixture is sucked into crankcase while
First one is compressed in cylinder
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15. 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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16. Blow-by adds to crankcase compression
What is going to happen when the piston gets here?
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17. Power/Exhaust Stroke (TDC-BDC)
Still closed
Exhaust port is uncovered and exhaust starts leaving
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18. What’s going to happen when the piston gets back to TDC
OK, I get it !
ANOTHER POWER STROKE
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19. Every time the piston reaches TDC, there is another power stroke !
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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. Let’s make a chart
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26. Let’s make a chart
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27. Let’s make a chart
Will be on Quiz
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28. Reed valve on the side of crankcase
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33. Tuned Exhaust
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34. Tuned Exhaust
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35. Tuned Exhaust
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36. Tuned Exhaust
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37. Power stroke every revolution
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38. Let’s watch CDX Disk 4-1 Look for two stroke with no reed valve
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40. 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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41. 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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42. 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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43. 32 to 1 Mix Think . . Think . . Think . . Think . . Think
5 gals X 128 ozs would give me ozs of fuel
How am I going to figure this out?
20 oz of oil for 640 oz of fuel or 5 gallons
640 ozs of fuel divided by
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
128 2
X 5 32
640 64
640
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44. 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
You figure it out
Let’s say we are going snowmobiling for the
Weekend and you have 1 quart of two stroke oil
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45. 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
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46. There is always more than one way to figure something out
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47. 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
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48. Measure, don’t guess! 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!
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49. 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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50. 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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51. 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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52. 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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53. Multiple cylinder two strokes
The crankcase below each piston has to be sealed to create crankcase compression for that cylinder
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54. Two stroke engine questions?
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