blew spark plug out!

Discussion in '2-Stroke Engines' started by crabdance, Aug 17, 2008.

  1. crabdance

    crabdance Member

    Well... I have been trying to trouble shoot why my bike has lost power since I put another carburetor on it and one thing I tried yesterday was to get a new plug. Since the NAPA store couldn't find a replacement plug I looked on the board and found a recommendation for a replacement.

    This morning when I took the bike out for a ride, it went about 300 feet and then the spark plug blew out the top of the motor! Needless to say, I'm not overjoyed at the moment.

    My question is this. What is the likely damage? Am I going to need a new engine? New Head?..... I could go on but I don't know enough about these little engines.

    I would really appreciate any help with this. This little bike has become my friend and I really like riding it everyday. It will be sad if I can't ride.


  2. arceeguy

    arceeguy Active Member

    You can buy a heli-coil thread insert kit to fix the head, but I wonder what caused the engine to puke the plug in the first place?

    Usually, when a small engine spits out a plug that wasn't cross threaded, it is because the plug wasn't torqued down tight enough. The plug cannot dissipate heat to the cylinder head, and gets so hot it melts the aluminum and shoots out of the head. A lean mixture will cause combustion temperatures to skyrocket too, but usually the piston will burn or seize before anything else. Since you only drove the bike a few hundred feet, there really wasn't enough time for the above scenarios to happen. Maybe the new plug had slightly different threads and didn't fit quite right?

    I would try and buy a used head from a member here, since the heli-coil kit with tap, inserts and required tools is probably more expensive.
  3. hill climber

    hill climber Member

    try sraewing it back in it may have just vibrated out if not remove the head and take it to a local machine shop/auto repair facility. spark plug threads are ofter mift and repair is simple
  4. crabdance

    crabdance Member

    Thank you

    I have to say thanks to both of you and You are both right about the problem I had. The plug was not in there tight enough and vibrated loose and just shot out. I just tried to put the plug in and road around the block like nothing ever happened.

    Forgive me for being such a dummy. I always think the worst. I am just SO relieved that it was only that wrong with it and not something else. So my bike is running and happy and I'm happy once again too.

    Oh, and I also put the plug in tighter this time. Not TOO tight but enough to hold it in there.

    thanks for being there guys,
  5. srdavo

    srdavo Active Member

    this might be the cause of your lost were prolly losing compression around the sparkplug hole.

    I agree with arceeguy.... someone will have an extra head & gasket lying around.
    Last edited: Aug 17, 2008
  6. arceeguy

    arceeguy Active Member

    Glad to hear it wasn't a major problem!

    I assumed that the threads were stripped out when the plug came out, but you know what they say about assuming anything!
  7. crabdance

    crabdance Member

    Believe it or not I could screw the spark plug right back in. There is a small place at the very top where the thread is out a little but the plug will still go back in.

    I'm just happy that it wasn't anything worse. I went to my neighbors house and asked for a shot of whiskey (didn't really drink one). He said "wow" what's up? I told him about it and he's the one who said it might just go right back in.

    I'm just SOOOOOOOOO happy that everything is ok and nothing serious happened. I was bummed there for a while.
  8. spad4me

    spad4me Member

    Did you use antisieze compound on the new sparkplug?
  9. crabdance

    crabdance Member

    No.... don't know what that is??? (other than the obvious)
  10. Skyliner70cc

    Skyliner70cc Active Member

    Don't use antiseize. it isn't required and could put you at risk of stripping the thread if you do use it. Antiseize use requires about 50% less torque to be applied or you overstress the threads and risk stripping them. Lots of folks dont' know this.
  11. crabdance

    crabdance Member

    Thanks Skyliner.... Now I will know this if it ever comes up. Thanks for the advice.
  12. crabdance

    crabdance Member

    I'm wondering about something. Since all I knew at first when I got my used motor was a leaking carb that had a lot of power. Now I've got another carburetor that doesn't leak but doesn't have the power. Is it possible that what I am experiencing now is normal for a 2 stroke when it comes to power? When I come up a medium size hill I lose about 5 mph. When I take off it takes longer to get up to speed. Is it possible that what I am experiencing now is normal and I just don't know it?

    I've been trying and trying to find out why my other carb just doesn't have the power that my gas leaking carb did. What do you think?

  13. Pablo

    Pablo Motored Bikes Sponsor

    Really the chengine won't have as much power as you "expect" until you match the manifolds to the ports and put a tuned expansion chamber on.
  14. crabdance

    crabdance Member

    Thanks Pablo, I think my theory might be correct then... or possibly correct.
  15. tpelle

    tpelle New Member

    This thread brings back memories of when I was a kid.

    My dad - who lived through the great depression and learned thrifty ways - never owned a new lawnmower. He would just keep his eye open on trash-collection day, and if he saw a lawnmower out by the curb for pickup, he'd stop and throw it in the back of the car. (Used to embarrass my mother to death!) Then he'd mix and match parts until he got one running. He always had four or five lawnmowers in some stage of Frankenmower resurrection!

    Of course, some of these mowers could be hard to start, and with it being my job to mow the grass, I learned all sorts of tricks to get 'em running and keep 'em running, including cleaning and gapping the plugs.

    One day I guess I didn't get a plug back in tight after taking it out for cleaning/gapping. That puppy got launched by that Briggs & Stratton spark-plug-missle launcher, and nailed me right on the right shin bone! Man, did that ever hurt! I thought I'd been shot!

    Crabdance, it occurs to me that, if this was a frame-mounted engine that launched it's plug, you should consider yourself lucky that you're not singing soprano in the choir!
  16. crabdance

    crabdance Member

    thanks for your story. And yea, things could have been a lot worse (he says in a high voice). Yea, it was a frame mount. I'm just glad that nothing really bad hapened. I thought I had killed it at first as I was walking it back to the house. All kind of things were going through my head about how bad the damage was. Little did I know that I could just put the plug back in and keep going. What a BLAST!
  17. eleseur96020

    eleseur96020 Member

    Even if you did blow the upper assembly they are only $50ish bucks new. I know that most of the peeps on this thread are thrifty and would never dream of buying a new upper assembly (me included), but it is good to know that you don't have to buy a whole new engine when something catastrophically fails.