What happened to my bike???

Discussion in 'Frame Mounted Engines' started by purpmunk, Mar 10, 2008.

  1. purpmunk

    purpmunk New Member

    I have a 70cc 2-stroke and I took it down a bridge full throttle to see how fast it could go after a good 2 tank break in, about 100-120 miles. It was going fine until I got to the bottom of the bridge. I let off of the throttle a little bit and the engine locked up on me. I had to move the wheel back and forth a few times to get it to free up. So I took the top off of the motor and noticed that a very small piece of what looked to be the piston had chipped off. I was wondering if this very small piece could affect the compression of the piston. My guess is that I need either a new piston, or a whole new motor.

    Also, I noticed that the ends of the wires coming from the motor had burned holes in themselves. Not sure how this happened. If anyone knows what happened or has any tips, that would be great.

  2. Dude. How fast were you going?
  3. gone_fishin

    gone_fishin Guest

    "down" anything at full throttle isn't good...

    if your info is accurate: i'm betting you will find more physical damage.

    the electrical? just a dummy answer here...i'm guessing that maybe you pumped the magneto to the boiling point. someone who knows, is that possible?

    tear it down and give us pics...we have successfully rebuilt these things online, but you're gonna have to do your part.
  4. will_start

    will_start Member

    wow, this ones going to be interesting, cause its my greatest fear come true, engine has something serious.
    Hang in there PurpMonk, these guys will help you through.

  5. gone_fishin

    gone_fishin Guest

  6. fetor56

    fetor56 Guest

    By the sounds if it your gonna atleast have to pull down the top half of the engine.I've never had the need to do it but it shouldn't be that difficult...theres plenty of threads about it here.
    Weigh up yourself weather it's going to be worth it...either fix that engine,or if u have the finances get a better engine and keep the original one for spares.
    If i liked the engine i'de keep it and any parts i'de replace with something better(if available)
    Look at it as a good learning experience,unwanted but good.
  7. purpmunk

    purpmunk New Member

    me again

    It was at night so I couldn't really see my speedometer. But I would guess a good 40-45 mph. I know, I know, way too fast for the little thing. Trial and error at it's best. I'm just lucky I didn't bite the dust when my rear wheel locked up on me. I skidded for a good 50 feet, and luckily kept my balance on the thing. I tried to take the motor apart this morning but stripped one of the screws above the clutch housing. Oh well, guess I'm gonna just get a new engine.

    I was wondering if anyone knows (and I'm sure someone does) where I can get my hands on a better exhaust pipe. I just wanna lower my rpms at around 30-35, so I don't blow the next engine and for a little better gas mileage.

    Thanks for the advice Augidog. No more full throttle. I want this next engine to last me a little while. It really got me p.o.'d, I only rode on this one for 3 days when it blew out. Thanx a million.
  8. graucho

    graucho Active Member

    Sorry to say i think you bike went "nite,nite" Im sure you did damage to the sleve, rings, crank. Sounds like you went way over "Red line" Ive had to learn the hard way on a 5,000.00 street rod motor. This is why I switched hobbies 10 years ago. These engines are WAY cheaper.
  9. mshagg

    mshagg New Member

    So is this realistically the only way you can push these engines past their engineered RPM limits? i.e. pointing the bike down hill and pinning it?
  10. Yes. I don't understand it,though. You go faster down a hill with the clutch in.
    RIP Happy Time. :cry:
  11. cooltoy

    cooltoy Member

    That, along with shutting down the throttle as he got to the bottom of the hill. There was no fuel/oil going to the engine and it was as "lean" as possible at a time when the engine really needed that oil!!!
  12. graucho

    graucho Active Member

  13. Papasaun

    Papasaun Guest

  14. Scottm

    Scottm Guest

    I greatly admire your honesty. It is soooo tempting to want to run WOT and then some. If you want to try and rebuild PM me. I've had the same lock up and engine debris, and went through a rebuild that Augi posted.

    Good luck!