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

What’s the Difference?

https://www.youtube.com/watch?v=hV3LImCslpo

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 bikesMopeds, Jet skis, Small outboard motors, Remote controlled

planes

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

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

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 strokeis happening beneath the piston).  

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. 

Operation of Two-stroke

How Stuff Works Link

Things to watch:Spark plug firing Piston acting as a valveWhere air/fuel/oil mixture enters

Why aren’t 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

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

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

How Much Oil do I Need?

Look at the side of the bottle

OR

(Gallons x 128) / Desired Mixture= Ounces to add

How much oil do I add if I have a 5 gallon gas can that is half full to reach 40:1 mixture?

Generate a list of pros & cons with your partner!