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2 Stroke? 4 Stroke? WHAT DOES THAT MEAN??

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  • 2 Stroke? 4 Stroke? WHAT DOES THAT MEAN??

    I am a new boat owner, what does 2 Stroke/4 Stroke mean? Is there a 6 Stroke? I am clueless. Someone please fill me in! Thanks!


  • #2
    Re: 2 Stroke? 4 Stroke? WHAT DOES THAT MEAN??

    G,day. A two stroke motor fires on every second stroke, many small engines in mowers and small motor bikes use 2 Strokes. four stroke motors fire on every fourth stroke. most auto engines are four stroke.two stroke advantages:- cheaper, lighter, will generally rev higher. disadvantages:- more pollution, you have to burn oil in the fuel to lubricate, less energy efficiant.Four stroke advantages:- better fuel economy (usually). quieter. less pollution.generally service charges are more for a 4 ST as you have to change oil and filter but this is offset by not having to buy 2 stroke oil.The DFI motors like Merc optimax or bomb FICHT have some of the advantages of both systems but are VERY expensive to purchase. Hope that helps

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    • #3
      Re: 2 Stroke? 4 Stroke? WHAT DOES THAT MEAN??

      We need to clarify "stroke" a little. In a 2 cycle (2 stroke) motor the spark plug ignites the compressed fuel/air every time the piston comes to the top (nearest the cylinder head) of the travel. In a 4 cycle (4 stroke) the fuel/air mix is ignited every other time the piston comes to the top. There are 4 things that must happen to make power. Intake of the fuel/air mix, compression of the fuel/air, ignition (spark), power (piston being forced down or away from the head by the combustion). A 2 stroke motor does this in one revolution of the crankshaft (1 up stroke and one down stroke of the piston) and a 4 stroke gets it done in two revolutions of the crank (2 up strokes and 2 down strokes).The 2 stroke motors have made tremendous improvements in effeceincy with the development of direct injection and the latest electronic ignition management.Good question!

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      • #4
        Re: 2 Stroke? 4 Stroke? WHAT DOES THAT MEAN??

        Check out the following website. It is really cool!: http://www.howstuffworks.com/two-stroke.htm

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        • #5
          Re: 2 Stroke? 4 Stroke? WHAT DOES THAT MEAN??

          Some other important things... The 4 processes for both engines are the same....Intake, compression, power, exhaust. The 4-stroke (4-cycle) performs this sequence in 2 revolutions of the crankshaft. The 2-stroke (2-cycle) performs this same sequence in 1 revolution of the crankshaft. The 2-stroke accomplishes this by using intake and exhaust transfer ports that enter and exit the cylinder. The 4-stroke uses mechanical valves.The 4-stroke will have an internal pressurized oiling and filtration system. The 2-stroke will not.The 2-stroke will have a cage reed pedal intake which functions as as a result of engine resonance, and intake and backpressure forces. The 4-stroke has a completely mechanical lubricated valve train assembly (cams, lifters, rods, and usually multiple valves per cylinder), which is operated by a oil bath gear drive or a belt.2-stroke outboards don't have variable exhaust timing and therefore require a tuned exhaust system, which in effect narrows the powerband.The intake and exhaust design of 2-strokes inherently allow for poor scavaging (forcing out all exhaust gases and burning all intake fuel completely), which makes the engine less efficient and more environmentally unfriendly. It also makes them inherently produce more noise.2-stroke outboards don't always "rev higher". Most 4-strokes, like Yamaha and Suzuki's 4-strokes, actually rev higher than their 2-strokes.4-strokes usually come with a better (longer) warranty.Both are great outboards. Cost, weight, dealer service, emissions, longevity, resale, economy, performance, and overall enjoyment are usually the determining factors between the two.Hope this helps.

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          • #6
            Re: 2 Stroke? 4 Stroke? WHAT DOES THAT MEAN??

            Hahaha. I'll bet you got more than you thought you wanted on that one, Brian.Sometimes asking a question like that is like trying to take a sip from a firehose.There is more, if you are interested.Forktail mentioned that many 2 stroke-cycle engines use reed valves to admit the charge (fuel and air) to the crankcase. That is true of all 2 stroke-cycle outboards that I know of. . .but. . .many 2 stroke-cycle engines use either a piston port or a rotary valve rather than the reeds to time this action. Motorcycle engines and glo-plug model airplane engines are examples.Notice that I use the term, 2 stroke-cycle. That is the nit-picky correct term for an engine that uses 2 strokes of the piston to complete one cycle of operation. For the same reason, 4 stroke-cycle is the most correct term for that type engine.Now I'm sure you have gotten more than you wanted to know.
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            • #7
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              Re: 2 Stroke? 4 Stroke? WHAT DOES THAT MEAN??

              WOW! You guys really know your stuff! Thanks for the input!

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