I seem to have excessive compression

Discussion in '2-Stroke Engines' started by jefuchs, Dec 3, 2012.

  1. jefuchs

    jefuchs Member

    I have a brand new kit, and this is my first build. I haven't gotten the motor running yet.

    I thought my poor leg strength was my problem, but now I'm certain it's not. I got everything assembled, and tried to start the motor by keeping the bike stationary, with the back tire elevated, and applying pressure to the pedals... kind of like kick starting a motorcycle.

    The pressure I encountered was so high that it was like the brakes were on. I disengaged the clutch to be sure I didn't have something jammed, and things turned smoothly enough. With the clutch back in place -- it would barely budge.

    No kidding, I could stand on the pedal and not turn the motor (granted, I'm a very small guy, but it shouldn't be this hard). I pushed so hard I bent my kick stand. I could get it to push through a little, but not with enough speed to start the motor, and it definitely would have brought the bike to a screeching halt if the bike were in motion.

    So I removed the spark plug, and tried again. Things turned just fine, but I would have expected it to be a little easier with no plug. Still, it proved nothing was frozen. It's definitely compression.

    Is this just a new-engine issue, or is something really really wrong?

    I'm sending a copy of this post to the seller to see if they can resolve this.
     

  2. snarlofdisgust

    snarlofdisgust New Member

    first turn over is tough, find a big hill engage the clutch so the chain can spin and while going down the hill slowly engage the clutch. Pedal if necessary. It'll turn over.
     
  3. jefuchs

    jefuchs Member

    Thanks very much! We don't have hills of any size here, but I'll scope out something.
     
  4. wan37

    wan37 Member

    I have the same problem I have to be going pretty fast to get it to start.I got it so bad the it keeps sheering the key ways on the little beval gear.I wonder if somebody knows what we can do?I also had a pull start on and there's no way that I can pull it hard enough.
     
  5. wan37

    wan37 Member

    jefuchs the only thing I found to do is add another head gasket that's what I read in one of theses forums,but then we would lose a little performance.I don't know how much,but I got another gasket on order.I just want to make sure before I go and add another gasket.So if anybody can help It would sure be helpful.
     
    Last edited: Dec 4, 2012
  6. crassius

    crassius Well-Known Member

    Sounds like you have a beach cruiser with no gears. I've seen these geared so high that static starts require a VERY solid build bench that you can really stand on the pedals from. You may just have to live with pedaling real hard to get up enough speed to dump the clutch on it.

    Lowering compression may help, as would putting a smaller sprocket on the pedal crank, but you probably have coaster brakes too, so the rear wheel should completely die after a short while, allowing you to rebuild with a derailer back there to solve the problem.
     
  7. wan37

    wan37 Member

    crassius I'm having trouble on a mountain bike with gears.I really have it in the easiest gear too.
     
  8. crassius

    crassius Well-Known Member

    I've never seen one so stiff that it wouldn't start in first or second gear. If you're sure that it is turning freely (nothing binding) when you have the plug out, then I'd try to start it downhill or something to see if it loosens up pretty quickly (10 or 15 miles). If not, then you might need a second head gasket.
     
  9. wan37

    wan37 Member

    I have been through a half a gallon of gas already and it hasn't loosen up yet.I can get it started but very very hard.I'm tired by getting to start.So I guess the double head gasket is the thing to do.
    i was on here to see if any body agrees about the double gasket, or has a better idea.
     
  10. jaguar

    jaguar Well-Known Member

    For one, you weren't real clear about whether it was still hard to turn over with the spark plug out. If the plug is out and its hard to turn over then you have a bad bearing somewhere. It should turn very easily with the plug out. I don't care if it's new.
    If it turns over easily with the plug out then you obviously have too high a compression. Add one or two more head gaskets.
    I'd be curious to know the exact engine you have and whether or not the head is something special they put on there. Normally the Chinese two stroke engines have very minimal compression so that the cheap bearings will last.
     
  11. wan37

    wan37 Member

    Yes Jaguar It turns easy over easy with plug out,but it takes a lot to start got to go really fast.Oh it's a Z280 cc engine kit from bgf and stock head.I got about 50 to a hundred miles on it and onces it's started it runs really good.
     
  12. jaguar

    jaguar Well-Known Member

    Yes high compression makes engines run more effeciently (more power) but wear bearings faster. And in your case is harder to start. If you want to keep the high compression then you could try to find an old lever controlled compression release. Ya gotta acquire the feel for using them right but they do work. You'll need an extra spark plug hole in the head to screw it into.
     
  13. wan37

    wan37 Member

    hmm thats and idea ,but would rather not wear out the bearing.I also don't want to lose power tho hence it's got good power once it's started.
     
    Last edited: Dec 4, 2012
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