high compression on ht engine

Discussion in '2-Stroke Engines' started by dougsr.874, Jul 23, 2010.

  1. dougsr.874

    dougsr.874 Active Member

    I installed an 80cc ht engine on my bike....the engine turns over fine with the plug out....but it will drag the back tire trying to turn it over to start it.....ruined the clutch pads by adjusting the clutch tight enough to turn over the engine. once started it runs ok.....will adding another head gasket solve the problem. Otherwise I am at a loss,,how can I fix this?
     

  2. AussieSteve

    AussieSteve Active Member

    When you get up to speed and engage the clutch, keep pedalling and the wheel won't lock.
    Another head gasket would make a slight difference, but would also reduce the engine's already meagre power.

    How do you mean "ruined the clutch pads"?
     
  3. professor

    professor Active Member

    Are you sitting on the seat when this happens?
     
  4. dougsr.874

    dougsr.874 Active Member

    try to clarify the problem

    with the clutch adjusted what I would consider normally, the clutch would not turn the engine over....so I tightened the flower nut (thinks it called) on the outer clutch assembley(the part with the 3 studs sticking out of) I am under the impression that by doing this it puts more pressure on the clutch pads....What happened to the pads is:::::when I removed the clutch cover to inspect it there was lot of clutch pad dust and the pads were worn, black and shiny ,,,so much so that tightening more had no effect.....Yes, I was sitting on the bike...also, this engine came as a dual start engine, which was almost impossible to pull with the recoil starter...that starter promptly broke after my son exerted enough effort on it to pull it..This thing has got me stumped, unless it the compression.......
     
  5. AussieSteve

    AussieSteve Active Member

    That's how the pads usually look. The pull-starts often break, from what i've heard.
    These engines are a bit hard to turn over, but not usually too hard for the clutch to handle.
    I would have suspected the plug hitting the piston except that you said it runs OK once it's going.
    Got me beat. Do a compression test. My 66cc (flat head) was 115psi standard. (142psi now, with hi-compression head. That's hard to turn over.)

    Is yours a flat or slant head? (The slant heads have higher compression.)
     
    Last edited: Jul 23, 2010
  6. Al.Fisherman

    Al.Fisherman Active Member

    If it runs well, if and when you get it started, we can eliminate other issues. Add one thin gasket at a time. If you use aftermarket thin gaskets, make sure the hole diameter (bore) is the same as those installed (measure one against the other pre instillation). I've never seen one that needed a added gasket to just start, but you may have a tight ringed engine. Weight of rider has some to do with starting. I (210#) can start my bike easier then my (135#) son.
     
  7. motorpsycho

    motorpsycho Active Member

    by tightening the flower nut, you are moving the clutch pads closer to the fly wheel, which will make them drag more, and wear out faster.
    adding another head gasket will decrease compression, but you will also loose performance.
    i would adjust the flower nut back to "stock", and do as aussiesteve said..get the bike moving by peddling, and then when you let the clutch handle out, keep peddling.
    i think that you just have tight piston ring to cylinder clearance, and they will wear over time and get easier to turn over.
     
  8. GearNut

    GearNut Active Member

    There is also a chance that the clutch spring inside the engine cases is not set tight enough.
     
  9. dougsr.874

    dougsr.874 Active Member

    Update: Having temp. shelved this engine, I installed a completely different, but same model engine on another bike.....It starts and runs perfectly,,,,amazing the amout of difference in same model engine?????????????
     
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