blown motorized bike carnage!

Discussion in 'General Questions' started by thunderhead289, Mar 22, 2014.

  1. thunderhead289

    thunderhead289 New Member

    finally granaded off the motor. the rings look pretty bad as I am pretty sure they( with all the blowby) had something to do with it.

    here is the video of the engine carnage, enjoy

  2. cpuaid

    cpuaid Member

    I have 3 blown HT engines that i never even bothered to disassemble and found the video very informative. 2 of mine blew less than 1000 miles, 1 at a little over 2000 miles. at least you were able to get 1800 miles out of yours. thanks for sharing.
  3. EastSideRider

    EastSideRider New Member

    my piston keeps getting i've had the engine for a month maybe more been trouble shooting ever since doesn't have a mile on it what should i do PLEASE SOME ON HELP
  4. butterbean

    butterbean Well-Known Member

    Your piston keeps getting what? Very hard to understand your post.
  5. darwin

    darwin Well-Known Member

    Do you think those 2 strokes grenade because of running them lean with oil in the mix? Landscaping cos abuse their 2 stroke stuff and they seem to go from year to year running till they wear out.
  6. thunderhead289

    thunderhead289 New Member

    they grenade because they are usually poorly balanced and are under a load much greater than most lawn 2 strokes.

    these engines are just loose. when you think of the run time of the bikes under a load vs the lawn 2 strokes under a load, they are roughly the same. oil and air fuel ratio have little to do with it as long as they are adjusted marginally correct.
  7. butre

    butre Well-Known Member

    Landscapers rarely hit 3000 rpm though, it's not unheard of for people to push 7 or 8 thousand RPM with a ported jug
  8. thunderhead289

    thunderhead289 New Member

    and the fact that we consistently run at 4 to 6 grand normally with minimal cooling fins compared to your average two stroke
  9. Fabian

    Fabian Well-Known Member

    My experience is that once you move away from 25:1, the life of a Chinese 2-stroke centre mounted bicycle engine decreases significantly when asking the engine to deliver continuous output at close to maximum usable power.
  10. jaguar

    jaguar Well-Known Member

    for the benefit of all I hope that anyone who has had a blown engine will share all details such as
    engine oil used
    at what ratio
    size engine
    any modifications to engine (compression increase, porting, carburetor, exhaust pipe)
  11. thunderhead289

    thunderhead289 New Member

    -25:1 oil ratio
    -66cc (generic but not bgf)
    -boosted compression by shaving my original head
    -carburetor set to one notch richer on slide pin
    1 hole drilled through my old-style exhaust pipe baffle tube for a very slight increase in flow due to the compression increase.
    -boost bottle
    -wallmart brand 2 stroke oil (yeah I know shame on me)

    rings were pretty worn down. minimal carbon for such mileage. ran it good and rich, just ran it pretty hard in the rpm's. lasted many miles for what I put it through. rings failed due to the fact that they are simple iron rings. I do SBF & SBC builds and always use moly coated rings(what all cars run today). those iron rings only last 80 thousand on a car tops and they aren't running between 3500 to 5500 rpm none stop.

    wristpin wear was very very little despite the deformed wristpin. could not feel any up and down play in the connecting rod.

    ran darn good right up until its final wheelie. was actually still running on that junk, I just shut it down because I knew it was had and did not want shavings going into crankcase.

    bottom end is still very solid. 35 dollars in parts waiting at home to completely redo the top end. will make a vid on that when I do it so all can see how that's done.

    there I do believe I have explained myself.
  12. jaguar

    jaguar Well-Known Member

    you mentioned worn out rings but not what actually caused you to want to shut it down and then rebuild it
  13. thunderhead289

    thunderhead289 New Member

    well there is one problem here then. watch the video from my original post. that should really help you to understand in detail. I think that is what you are missing here sir.

    I take an in depth look at the aftermath.

    I was riding a wheelie and it started to loose power and make a metal on metal noise as it ran. was backfiring and popping with minimal compression.
  14. jaguar

    jaguar Well-Known Member

    OK I just watched the video but am still not sure what loose metal thing was responsible for the damage.
    You suspected the rings since one was broken. Looking at what is left of them can you see that one small piece of it is missing? If so then that would be the prime suspect.
  15. thunderhead289

    thunderhead289 New Member

    okay I understand now. when the rings where, they do not just wear away from the side, but the piston also wears in the slots where the rings run in. when this happens the rings develop some play and can rock back and forth. on these two strokes with port valves eventually the rings will catch a port lip when they develop play like this and then that's the end.

    ring to piston play and ring too wall play was enough to do this. I believe this is what happened and it broke the ring that caught.

    this is why when engines are built there is usually a piston to ring clearance.

    are you jaguar CDI btw?
  16. jaguar

    jaguar Well-Known Member

    yes I make the Jaguar CDI

    Are you aware that the excessively advanced timing on these engines greatly increases the combustion pressure (before it can do any good) which seeps behind the rings and causes excess outward ring pressure on the cylinder?

    so do you think the cheap oil had something to do with the rings getting too much vertical play?
  17. jaguar

    jaguar Well-Known Member

    don't increase compression without a Jaguar CDI

    With the excessively advanced ignition of the standard CDI the peak pressure happens too early which is not that horrible on a low compression standard engine but when you shave the head for more compression it takes the whole shebang into the danger zone as you have found out the hard way. That excessive combustion pressure
    1) wears out conrod and crank bearings too soon
    2) increases engine temperature which can cause detonation and engine failure if there is a lean fuel mixture
    3) causes too much outward ring pressure onto the cylinder which increases possibility of the ring catching on a port and causing unrepairable damage

    On my site I warn against increasing compression without a Jaguar CDI but some people think that's just promotional talk.
  18. thunderhead289

    thunderhead289 New Member

    well this seems to validate some of your claim. iv always believed the ignition advance on these engines to be too retarded and that's why they cant pull very high rpms.

    what degree of initial advance are these bikes set to?(which is also the total I imagine as there is no progressive advance correct?)
  19. thunderhead289

    thunderhead289 New Member

    on the aspect of compression vs the failure, I note that there will always be quicker ring wear and blow-by conditions with heightened compression along with less bearing life. it makes for a much more potent explosion. so naturally the rod bearings take a beating.

    the biggest problem I could see with the motorized bike is that the cdi will not be at the right advance and if too far advanced(which leads to detonation) can really do a number on these cast aluminum pistons and bearings as the piston will be fighting the compression fire(too much advance)

    if its retarded that's fine, but too much advance with too low grade of fuel(higher octane can withstand higher combustion pressures) I can see these not living long at all.
  20. jaguar

    jaguar Well-Known Member

    click on my signature link and go to the CDI page to see the ignition curve of the standard ignition as well as that of the Jaguar CDI