difference in a 4 stroke and 2 stroke motor

Discussion in 'Motorized Bicycle General Discussion' started by dumpstercrusher, May 21, 2013.

  1. dumpstercrusher

    dumpstercrusher New Member

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    whats the difference between the 4 stroke motors and 2 stroke besides the less moving parts on the 2 stroke? more reliable? i know 4 strokes can be a little harder to put on a bike due to it being a larger motor. would need a wider pedal crank
     
  2. dodge dude94

    dodge dude94 New Member

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    4 strokes are more reliable by far, but heavier.
    If you want a toy to putz around with and make folks smile -> 2 stroke.

    If you want a MACHINE that can actually get you to work without requiring registration (well, in some areas) -> 4 stroke.

    Just my 2 cents.
     
  3. biknut

    biknut Active Member

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    That really depends on a lot of things. If you ask Saca who's bike has been more dependable, his 4 stroke, or my china girl, I'm pretty sure he'd say my china girl.

    [​IMG]
     
  4. dodge dude94

    dodge dude94 New Member

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    ^That's an old engine though.

    Can't go wrong with Honda!
     
  5. biknut

    biknut Active Member

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    Not just engines have trouble.

    There's many a slip twix't a cup and a lip.

    .girl.:ride:.ride3
     
  6. dodge dude94

    dodge dude94 New Member

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    DUDE, wait, WHAT?
    lol
    I think I got that.
     
  7. maniac57

    maniac57 Old, Fat, and still faster than you

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    Four stroke BICYCLE engines have a better rep for reliability due to the china two stroke being so poorly made.
    In the world of quality engines, the piston port two stroke RULES dependability due to fewer moving parts to fail.
    It's a judgement call but until china two strokes improve (it is slowly happening) the four strokes are slightly more dependable.
    That being said, I have always preferred two strokes for simplicity and ease of repair.
     
  8. dumpstercrusher

    dumpstercrusher New Member

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    i sure do like the idea of fewer moving parts lol
     
  9. dumpstercrusher

    dumpstercrusher New Member

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    hows that bike frame wit the tank combined with the frame? worth the money if you want to build a bike??
     
  10. biknut

    biknut Active Member

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  11. nerobro

    nerobro New Member

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    You're mixing up a few things here. But ... lets see if I can't make it make sense.

    Piston engines run on the Otto cycle. That is the classic suck, squish, bang, blow.

    4 stroke engines, typically have two sets of valves, and a geared camshaft to ensure all of those functions happen at the right time, and right order. So, on a 4 stroke, the piston travels down, with the intake valve open, and the exhaust valve closed. This sucks in air and fuel. At the bottom of the stroke, the intake valve closes, and the piston travels up, compressing the air fuel mixture. At the top, you get the bang, when the spark plug does it thing and ignites the fuel air mixture. This heated air pushes down on the piston and this is where you get the engines power from. At the bottom of the stroke, the exhaust valve opens, and the piston travels up again, pushing the burnt air out. "Blow."

    This segregated, and carefully timed process means you get to burn most of the air in the cylinder EVERY OTHER rotation.

    Two strokes... are a lot more funny. They manage to squeeze all four processes into two strokes. We'll start the description with the piston at the top of the stroke, with compressed fuel and air in the cylinder.

    The spark plug fires.. and the piston starts traveling downwards. About halfway down, a hole opens in the side of the cylinder wall, and the burnt gasses start rushing out. This air has momentum... this is important to remember.

    3/4 of the way down, a hole opens on the opposite side of the cylinder. That hole leads to the crankcase. The air and fuel is under a little bit of pressure, and assisted by the rush of exhaust gets blown, and sucked, into the cylinder.

    This is a messy process, so most of the time not all of the air really gets exchanged.

    The piston starts moving up again. Closing off the hole in the cylinder wall. (and in our engines..) The skirt, as it travels up, also opens the passage to the intake manifold, and carburetor. The piston traveling up, sucks fuel and air into the crankcase.

    As the piston travels, it also closes off the exhaust port. Now the cylinder is sealed, and the engine is compressing the air and fuel mixture, getting ready to spark the spark plug and start the next cycle.

    So... why did I explain all of that? 2 stroke motors are "tuned." Like a tuba, or trombone. They work really well at certain speeds, and throttle positions, but when they're not operating at their ideal rpm range (which is pretty short on most motors) their torque is very low.

    Between disk valves, or reed valves, a good tuned pipe, and a few other tricks, 2 stroke motors can get absolutely clean air in their cylinder, and make lots and lots of power, at certain RPM. Sadly, they don't operate there much. The classic 2 stroke sound is actually the motor 4, 6 or 8 stroking, because they're not getting enough clean air in the cylinder to burn. So the motor skips a few cycles as good air cycles in.

    4 stroke motors make good torque at very low rpm, and their torque curve falls off in a smooth fashion. 2 stroke motors make low torque at low rpm, good torque at their operating rpm, and very low torque when you exceed their operating rpm.
     
  12. biknut

    biknut Active Member

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    The beauty of a china girl engine is they're tuned for low hp, wide power band. You can run them down to almost 1000 rpm, and they'll still take full throttle, and run up to 7000 plus, which wouldn't be all that high of a rpm on a high hp 2 stroke.

    That's a good design feature for a bicycle with a motor.
     
  13. racie35

    racie35 Active Member

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    Only good thing about 2 strokes is its optional to buy one. Why those polluting pigs are still sold is beyond logic. If they were any good they be in cars,trucks and current bikes..instead they push em off on people looking for a deal----chainsaws,they work okay there,that's because power isn't as important as a sharp bladed tooth cranking fast...weedeaters too---same cheesy way out
     
  14. dumpstercrusher

    dumpstercrusher New Member

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    thanks for the posts! learnin a lot
     
  15. biknut

    biknut Active Member

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    The same reasons that make 2 strokes more desirable for chainsaws and weed eaters, also apply for motor bicycles.

    A big heavy 4 stroke chain saw wouldn't make sense. Same reasoning applies for motor bicycles.
     
  16. crassius

    crassius Well-Known Member

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    I hate mixing gas, but my arm can't do a pull start at all.

    also like the real clutch and low price of 2-strokes
     
  17. nerobro

    nerobro New Member

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    2 strokes don't need to be dirty. Run at high power levels, 2 strokes can be very, very clean. Injected 2 strokes can be astoundingly clean. (like pass euro 3 with flying colors clean..)

    The reason they're not in current bikes, cars, and trucks is due to their powerband. And people don't like the idea of having to add oil to their car.

    They're still common in marine use, where they're still accustomed to using oil with their gas.
     
  18. maniac57

    maniac57 Old, Fat, and still faster than you

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    The pollution issue is the ONLY reason two stroke engines are not everywhere.
    I think any four stroke that could compete equally with a two stroke would be so expensive and fragile as to be useless.
     
  19. dodge dude94

    dodge dude94 New Member

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    I will also add that in most cases (Scotto exempted here), 2 strokers just plain look cool.


    :D
     
  20. racie35

    racie35 Active Member

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    You should call gm and ford with the news!
     

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