cylinder ports size and location in cylinder?

Discussion in '2-Stroke Engines' started by Heathen, Aug 21, 2009.

  1. Heathen

    Heathen Member

    i have a 70cc engine that is giving me some headache, it has never ran properly cant get it to rev out to top rpm and has been low on torque.
    it has aslo guzzled gas, about 0-3-0.35 L / 10 km witch is a lot for a small engine. my other engines that run good does 0.2-0.25 L / 10 km.

    So i started experiment with different carbs with out any change, so i took the cylinder of one of my other engine and put that on. now it runs a lot better, not perfect but better it will rev up ok and has a lot more torque.

    So i'm guessing that the ports in the cylinder might be misaligned or something perhaps a bad casting( casting cores not properly fitted when they cast the cylinder)

    does any anyone know how the ports should be located inside the cylinder to allow these engines to run properly, can someone measure out a cylinder that is good so i can make sure i get a hold of a cylinder that is ok.
    would be nice if it where measured in metric system but imperial works as well i can use a calculator to translate... i hope :jester:


  2. biken stins

    biken stins Member

    what kind of engine ?
  3. toolow

    toolow Member

    im having the same problem
  4. biken stins

    biken stins Member

    Muffler/exhaust pipe.
    The one that gets over looked so often is the muffler.When they get pluged up it slows the engine a lot. Take it off clean it or just fire it up without it.
    If the engine ran and now there is a loss of torque doubt if it is the cylinder. Unless it was not broken in right.
    They don't cost much $12-15.
    Good luck.
  5. Heathen

    Heathen Member

    In my case it never ran right so it ain't the muffler, When i switched cylinder with my other engine it suddenly start to run more as it should not quite perfect though. the compression was also raised a lot wich is prolly why it runs a bit better.
    the cylinder i use right now is not perfect either couse when the piston is all the way down in the borr i can only see half of the ports coming up from the crankhouse, wich is no good. gonna try and fix that by removing some material of the edge of the piston to make the air/fuel flow more freely or add one or two gaskets under the cylinder to raise it.
    while i make those changes i'm gonna try measure up the cylinders/top and pistons to see what the difference really is.

    oh btw the engine is a cheap HT modell with centrifugal clutch.