Seized Piston?

Discussion in '2-Stroke Engines' started by MachoMouse, Dec 12, 2008.

  1. MachoMouse

    MachoMouse New Member

    Hello, I have been riding my 80cc (66cc?)motored bike 5-6 days a week for the last 4 months...I followed as many of the suggestions for the break in etc as I could and felt like I had gently brought the motor into a fully broken in state...It has performed very well for trips from 5-30 miles...I would say I have somewhere around 500 miles on it...well tonight I think my engine seized and I have no idea why...It was running very smoothly today, I rode about 20 miles in 5 mile increments...then I popped out for a quick trip to home depot and then pow! clunky engine noise follwed by stalling out..I tried restarting once, which was rough and the noise I heard made me shut it off immediately...kind of like something clunking around in the front of the engine...I rode home about 1/2 mile and took the top of the head off...there were a few salt grain sized pieces of metal in there, with maybe 5 or so simlilarly sized holes along the edge of the piston...the bike rolls with the clutch in but freezes the back wheel when the clutch is out...I took out the little pieces, replaced the top of the head and tried pedaling very fast only to have the bike skid when i let out the clutch...The piston seems to be frozen in place...I've never been able to remove the clutch plate, as the screws that came on there were of the "strip-o-matic" variety..
    ..I read some posts on here regarding the "woodruff key" (is that correct?) I can go and buy the drill bits to try to get them out if I need to...although I'll be walking to home depot.....can anyone help!!??!! I really hope that I don't have to replace the engine...the bike is my main, daily transportation...

  2. stude13

    stude13 Active Member

    hi mm; pull the head and tap the piston out of the barrel. i think you will need a piston, rings, wrist pin, barrel and gaskets.
  3. MachoMouse

    MachoMouse New Member

    thanks for the info

    hiya stude...thanks very much for the insight...i'm going to begin the teardown/ordering process...I hope I can get it back to the smooth running beast it was before...I miss riding it already! :icon_cry: Any thoughts as to why it would seize?...I've taken the best care of it as I can, I was definitely hoping to get several thousand miles on the engine....running 32:1 synthetic blend marine 2 stroke oil...custom exhaust and lots of TLC...
    umm mr. moderators...should I post my progress?
  4. stude13

    stude13 Active Member

    sure, let us in on what you find. it isnt something you didnt do. it is about making a silk purse out sows ear. a ring might have hung on a port. an air leak might have happened. the poor quality metals used are very likely at fault. i tried to clean up the combustion chamber with a dremel and finally gave up. in fact after putting up with this **** four times im done with them. im now buying gopeds to power bikes. search--motormaker--and briggs style. you can motor a bike for almost nothing. and those motors run forever. i have 47cc that cost 100 delivered. you can back-half a scooter and just bolt it to your axle dropout and drive off. good luck mitch
  5. Mountainman

    Mountainman Active Member

    just some reasons for a seize may be

    you may find a broken ring
    over heated
    not proper oil
    cracked piston let us know what you find once broken down

    soon you will be back up and riding that THING
  6. MachoMouse

    MachoMouse New Member

    thanks for the help stude and mountain!...I'm not ready to give up yet!...I will certainly post my progress...I'd love to be a contributing part of this forum...Is there possibly a thread somewhere that details taking the engine apart to get to the piston rings etc..?
    It sounds a bit delicate, and I don't want to break anything else while trying to fix it!

    p.s. stude...I think in the long run, I'd like to try a custom build with a more reliable engine...HT tinkering is an awesome hobby, and breakdowns can be a chance to learn, but ultimately safe reliable transportation is what I'm looking wife lives 400 miles from me, I'd love to putt-putt there on a custom 4 stroke for $8 in gas!
  7. BSA

    BSA Guest

    if your running at 32:1 tbh I'm not suprised You've seized up. A lot of people would tell you thats the correct oil ratio, but in my opinion 20-1 or 16-1 is the best, for not only peace of mind but for longer lasting rings, and bearings ETC. I'm not worried about smoke or decoking however.

  8. srdavo

    srdavo Active Member

    I'd be concerned about the marine oil...... outboard motors are water-cooled?
  9. MachoMouse

    MachoMouse New Member

    oil ratio

    thanks for the tip BSA, I will certainly consider that in the future...

    would the failure happen so sudddenly if oil ratio was the case?
  10. Mountainman

    Mountainman Active Member

    yes - failure due to lack of oil can happen real fast

    surprized that so many want to run as lean as possible
    I have always went with
    a little extra oil is a lot better than running too lean

    if you are looking for some long lasting care free miles
    maybe a nice engine from Japan next time

    to remove
    take off the head
    as you pull on cylinder -- tap piston lightly with wood end of hammer

    ride that ting
  11. MachoMouse

    MachoMouse New Member

    oil type

    Hi...thanks for the piston removal tips...should i use a rubber mallet to tap?

    ...the oil I was adding says specifically synthetic blend for air cooled 2-stroke's from autozone..the bike really loved it when i idled and ran so much smoother...

    upon recalculating i was running about 20:1 ratio...always had a bit of oily residue on engine...i think it wasn't too lean, maybe it was though, it felt indestructible during the 16:1 days...i'm very curious to pull the motor apart...

    thanks for the instructions and tips everyone, I appreciate it very much!!
    I'm dying to get back on the road...

    ..oh, one thing i failed to mention earlier is that I rear ended someone a week before the heavy steel frame seemed like it was fine not even the rim or fender was bent...but could this possibly have contributed to the piston seizure?

    does anyone know of a piston removal thread with pics by any chance?

    p.s. where would i find a japanese engine? that like the 'robin'?
  12. arceeguy

    arceeguy Active Member

    You can have the "proper" oil/fuel ratio and still seize up a 2 stroke if the carb is set too lean. Other than the idle stop screw, there are no external adjustments on the carburetor. You can raise and lower the main metering needle to adjust idle and part throttle mixture, but WOT mixture is regulated by a fixed metering jet. If you run at high speeds, and the mixture is just slightly lean, the engine will self destruct, regardless of how much oil is in the fuel. Lean mixtures cause combustion temps to skyrocket, and they starve the engine of vital lubrication - which is a very small amount in any two stroke.
  13. Mountainman

    Mountainman Active Member

    for those pistons
    I have always used the wooden end of a hammer (handle) -- got some weight
    should tap right out

    well -- the Robins and Hondas seem to run forever

    I sure like that when I ride those THINGS
  14. MachoMouse

    MachoMouse New Member

    replacement parts

    Hi thank you for everyone's help and tips...although now I'm not sure that I can get replacement parts...I contacted Dax and they are not sure that parts will match up...I can't imagine that my only option is to replace the engine, any suggestions?
    Thank you everyone, your knowledge is priceless.
  15. Technocyclist

    Technocyclist New Member

    Piston seizure can also be caused by intake leaks. I suspect your intake gaskets might have been damaged during the accident or the needle bearings. I also had a piston seizure after a day when I fell from my bike. When I opened the engine, the needles of the bearings were stucked between the piston and barrel. No way I could remove the piston which was stuck in the middle of the barrel. And I tried everything, and it just won't budge. I just throw away the whole thing in frustration, but I retain the crankcase.
  16. Mountainman

    Mountainman Active Member


    thinking that the odds are about 99.9% that no
    your little rear ender caused no damage to your engine

    my grandfather spent a large part of his life
    buying motor cycles and cars from junk yards that had been totaled
    even after some real fast stops in accidents
    engines were fine

    ride that thing
  17. MachoMouse

    MachoMouse New Member

    well, that certainly gives me something to think about...I've been wrapped up in wife/weather stuff for the last few days, so I haven't yet had a chance to pull the motor apart...the bike felt a little shaky the day of the accident, but within a few days, it was running smoother than it ever had...curious...but I will for sure check the needle bearings etc, and report back...thank you again everyone for you help...
  18. duivendyk

    duivendyk Guest

    1)Don't use marine type oil in these engines,but use ordinary garden variety 2 stroke oil, nothing exotic or synthetic and don't go a higher than 25:1,20:1 is even better if the plug does not foul.The HT engines were designed decades ago when these ratios were SOP.Better to have a messy exhaust than a seized piston.You probably have a broken ring.Looking into the ports may give you something to go on.
  19. MachoMouse

    MachoMouse New Member

    Thanks...yeah, the marine oil may have been a bad ran sooooo smoothly for 2 months with it in there though!...I'll be pulling the motor apart soon and I'm sure I'll have more to post...thank you for your insight
  20. MotorMac

    MotorMac Member

    Take picts

    Take some pictures as you proceed with the teardown, It would be interesting to see what went wrong.