Two-Stroke Engines

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Two-Stroke Engines

• Two-stroke engines are used only in applications
  where the motor is not used very often and a
  fantastic power-to-weight ratio is important Lawn
  and garden equipment

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Whats the Difference?
https//www.youtube.com/watch?vhV3LImCslpo
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The Basics

• A two-stroke engine
• Is an internal combustion engine
• Converts gasoline into motion
• Is the most common car engine type
• 2 piston strokes per cycle
• 1 crankshaft revolutions per cycle
• Chain saws, leaf blowers, Trimmers, Snowmobiles,
  Dirt bikes
• Mopeds, Jet skis, Small outboard motors, Remote
  controlled planes

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About 2-strokes

• Less moving parts
• No valves
• Oil is mixed in fuel for lubrication
• engine can operate at any angle
• Spark plug fires during every piston stroke!
• Hotter, faster, lighter than 4-stroke
• Wedged piston increases air movement for intake
  exhaust
• Low fuel efficiency increased emissions
• Lighter, simpler, cheaper

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Operation of two-stroke engine

• Piston travels up
• Intake Compression
• Piston travels down
• Power Exhaust
• Plug fires EVERY piston revolution
• Requires proper amount of back-pressure
• Great power to weight ratio
• Twice power in half the time

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Intake Compression stroke
Intake.  The fuel/air mixture is first drawn
into the crankcase by the vacuum created during
the upward stroke of the piston through the reed
valve.
Compression. The piston then rises, driven by
flywheel momentum, and compresses the fuel
mixture.  (At the same time, another intake
stroke is happening beneath the piston).  
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Power Exhaust/Transfer Stroke
Power. At the top of the stroke the spark plug
ignites the fuel mixture. The burning fuel
expands, driving the piston downward.
Exhaust/Transfer Toward the end of the stroke,
the piston exposes the intake port, allowing the
compressed fuel/air mixture in the crankcase to
escape around the piston into the main
cylinder. This expels the exhaust gasses out the
exhaust port, usually located on the opposite
side of the cylinder. 
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Operation of Two-stroke
How Stuff Works Link Things to watch Spark
plug firing Piston acting as a valve Where
air/fuel/oil mixture enters
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Why arent they used in cars?

• Wear out much faster
• Poor lubrication
• Hotter faster
• Increased wear
• Two stroke oil is expensive
• 4 oz/gallon
• 1 gallon every 1,000 miles
• Inefficient
• Poor fuel economy
• Increased emissions
• Oil burning
• Unburnt fuel leaving engine

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Mixing Gas Oil

• 2 stroke oil is different than 4 stoke oil
• Never substitute 4-stroke oil in a 2 cycle engine
• Mix to manufacturer recommendation
• Generally located on the gas cap or tag
• Too much fouled plugs poor performance
• Too little poor protection, increased engine
  wear
• Modern 2 stroke oils need to be mixed lighter on
  vintage implements.
• Synthetic blends require less oil but are more
  expensive

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TCW-3
Quality oil will have a rating on the
label. This means the oil has been tested and
meets regulations Avoid oils that have not
been rated
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How Much Oil do I Need?
Look at the side of the bottle OR (Gallons x
128) / Desired Mixture Ounces to add
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How much oil do I add if I have a 5 gallon gas
can that is half full to reach 401 mixture?
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Generate a list of pros cons with your partner!