Engine Trouble compression problem?

Discussion in '2-Stroke Engines' started by Soundquist, Feb 4, 2013.

  1. Soundquist

    Soundquist New Member

    hi, i'm new to the forum. my bike was running fine until i took it apart to replace a gasket i had seen hanging from the bottom as a result of a loose case screw. during reassembly, i broke about a cm. off of a piston ring and foolishly tried to run the engine with the damaged ring in place. it seized up, the broken edge catching on one of the openings in the cylinder wall.i was able to free the cylinder from the piston after much horsing and cussing, to discover a small, L-shaped gouge on the wall of the cylinder. i filed and sanded it out pretty well and replaced the broken ring and put it all back together. the bike won't run.
    it turns over fine and i checked the spark by turning the wheel and it works fine, so, my question is how sensitive are these chinese kits when it comes to that piston? the compression seems okay, you can feel it in the spark-plug hole, and when plugged the bike seems about as hard to roll as it ever did. okay, a little bit easier. could a tiny air-leak between the piston and the cylinder be the cause of my bike not starting?
    -carl
     

  2. jaguar

    jaguar Well-Known Member

    I'd guess that as long as the rolling starting compression feels the same then that is not the problem. But compression can be lost at the crank seals and at the intake, between the carb and the engine.
    check for gas and spark.
     
  3. BigBlue

    BigBlue Active Member

    Take out the plug and put a small amount of gas in the spark plug hole. Put the plug back in and try starting.

    Chris
    AKA: BigBlue
     
  4. Soundquist

    Soundquist New Member

    Thanks for the feedback. Checked spark again this morning still looks good. Fuel bowl fills fine and tried a little gas in the spark plug hole a few times, no luck. I live on a hill so starting has never been a problem. Any ideas?
     
  5. jaguar

    jaguar Well-Known Member

    spark plug should be wet after trying to start it.
    it's easy to miss an air leak. do you know how to test for crank seal air leaks?
    yeah you have spark but you screw the timing all up by installing the magneto opposite of how it should be. a very easy mistake.
     
  6. BigBlue

    BigBlue Active Member

    Good point. Your timing might be messed up. If you removed the magneto, you may have installed it backwards or incorrectly. Here's some info. from Grubee on how to install it correctly:
    http://www.grubeeinc.com/USA/Magneto Mystery.html

    Good Luck,

    Chris
    AKA: BigBlue
     
  7. Soundquist

    Soundquist New Member

    Spark plug is wet. Not sure which is the crank seal, or how to check for leaks. You mean the magnet is backwards? I wondered about that.
     
  8. Soundquist

    Soundquist New Member

    Wow. Flipped the magnet and there she goes. Thanks guys. Had to ride the caveman bike to work for 2 weeks. Jeez. That idea actually occurred to me but i judged by the markings on the magnet that i had it right. Thanks again!
     
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