Big issue on first bike!

Discussion in '2-Stroke Engines' started by DJ Raizer, Jul 28, 2012.

  1. DJ Raizer

    DJ Raizer New Member

    Hello everyone!

    About a year ago i bought a chinese motor kit from a local vendor with the intention of building a bike for recreation and maybe light commuting. I spend HOURS on these forums soaking up all the info that you all kindly provide. Well the project went on pause for a few months due to finacial hardship. I am now getting back into it and as i tore into the top end to replace the studs and check a few other things, i found this:


    I sent the distributor an email... basically the same as this post and asked him whats going on here. is this normal? Also metioned that the rings dont go down that far even at BDC so it might not matter?

    That was 4 days ago and i havent heard a peep back. I am super eager to make headway on this build but im at a dead stop now.

    any input?

  2. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member

    Who sold you that piece of junk?
    Are the pieces in the crankcase?

    what brand of engine is it?
    Yes, it matters as the broken off pieces mess up the shape of your transfer ports
    for one thing.
    Last edited: Jul 28, 2012
  3. sp454e

    sp454e Member

    save yourself the headach buy a new motor. apiece of the skert can be logde in the bearing area can cause big problems this has happen to me when i had my 125. call better business beru. I have done this and got results.
  4. Greg58

    Greg58 Member

    What I would do is look for any sign of the pieces and give it a try, what do you have to loose? From what I see the edge of the break looks old and coated kinda like it was dipped that way. If it doesn't run right you will have the bike ready for a replacement engine. Or you can buy a top end kit and replace it.
  5. DJ Raizer

    DJ Raizer New Member

    I dont want to name the vendor atm because hes a pretty nice dude and is actually involved with the hobby. I still have a little hope he might reply. I got into this cuz i thought it would be cheap so buying another motor is a scary idea. I think im going to roll the dice and give it a try. I will clean up the edges of the fractures and inspect the crankcase for debris (ive shaken it alot and dont hear anything). Is there a way to get a glipse inside without spliting the case?

    PS thanks for all the replies! So far you guys have been 3x more helpful than my vendor ):
  6. Greg58

    Greg58 Member

    You can rinse it out with some break -in fuel mix and see what amount if any small fragments fall out. Dump it out of the engine on a shop towel to catch the debris for inspection.
  7. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member

  8. DJ Raizer

    DJ Raizer New Member

    How did you know?
  9. darwin

    darwin Well-Known Member

    DJ hit skyliner up in buy/sell he has a crapload of parts hes trying to sell. If no go then put an ad up saying you want a top end some has an extra to part with.
  10. DJ Raizer

    DJ Raizer New Member

    well after doing a bit of poking around on ebay and motor sellers sites, I see that this IS ACTUALLY somewhat normal! most cylinders have those places cut out! Mine is obviously screwed up maybe broke in casting or cleanup, but i think it will be alright. Stay tuned for a link to my upcoming build thread and thanks again!
  11. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member

    Yes, it matters as the broken off pieces change the shape of your transfer ports
    for one thing.
    Go ahead and try it if you must but your transfer port timing will be all messed up.

    Motovelo should give you a new cylinder which looks like it was damaged
    before it was assembled.
    There is not much quality control in Chinese bicycle engine assembly "factories"
    and they work on these engines on the floor.
  12. Big Red

    Big Red Active Member

    A new cylinder is only about $20 from the cheapo dealers. MotorBicycleRacing is right, It will affect the flow of fuel. I'm not saying it won't run like this, it just may never run right like this. I have one just like that in my shop I was gonna experiment with. Just ain't had a chance to "take a chance".
    Big Red.
  13. ddesens

    ddesens Member

    I had one come to me new like this also. Inspected the bottom end for loose pieces and found none. It ran fine from the start and is still running today.( about a year). These motors come in boxes from china on pallets. Most sellers we all buy from just take a box off the pile and send it to you. Never opening the box, much less disassembling the motor. The seller should replace the cylinder for you at least. If they want to be reputable.
  14. Fabian

    Fabian Well-Known Member

    I've encountered this problem before. It looks virtually the same as a rebuild i did for someone else. The guy tried to use brute force to drive the cylinder into the engine cases using the studs and nuts.
    The problem turned out to be that the machining was not taking all the way to cylinder gasket mating face, and the non machined ridge compressed the cylinder wall (which cracked) as it was driven into the engine cases.

    The new cylinder was properly machined and installed without any fuss.

    Your engine (if it has not been run and the broken pieces are only sitting in the bottom of the crank cases) is likely to be quite ok. Just turn the engine upside down and shake out the bits with a bit of help from compressed air to remove any other gremlins that might be lurking inside the cases.

    A new cylinder will have you back on your way
  15. V 35

    V 35 Member

    No, that cylinder itself may be OK, but the engine was slammed together, what does the bore look like ? Are you sure their aren't pieces in the cases. [ others' also asked that ] . If you want to use jug, grind or file off broken flash, so it won't fall into engine later.

    I agree, for what motors cost, it's best to buy a fresh one elsewhere, and use the bummer one for parts.
  16. DJ Raizer

    DJ Raizer New Member

    hey all...

    Thank you all for your help. I worked around this issue, ( file and polish and assemble anyway), and have FINALLY built the bike. If you want to check it out, you can see it here; First bike complete!!! Mostly...
  17. HeadSmess

    HeadSmess Well-Known Member

    chinas standards are lowering

    wow. nice. it looks like a factory modified part :) if there arent pieces in the case then definitely been dropped.

    hmmm. other than the fact that it IS broken, it looks fine...those bits are thin.

    the rings dont come down that far. they arent transfer ports but merely passageways so stuff can get to the transfer ports. dont even "support" the piston...

    i woulda stuck it together and started it regardless. shes all a ok mate!

    mind you if there were bits in the case...ida been screaming blue murder...possibly even if there werent bits!
  18. DJ Raizer

    DJ Raizer New Member

    Yea i inspected the case pretty thoroughly and found no pieces. The engine runs pretty good as far as im concerned; it 4 strokes alot if Im not accelerating, which i understand is somewhat normal?
  19. Big Red

    Big Red Active Member

    4 stroking happens A LOT but should not be considered normal operation. MOST of the time it's because you're getting too much fuel delivery to burn properly. Try a smaller jet size would be my first suggestion. My second suggestion would be to get a better exhaust system for the better flow it would provide. As a test you can try taking out the end baffle on that cheap chinese exhaust. If it runs better it says you have a carb/exhaust tuning problem. Personally, I dont even try anymore. Too much time and money for me trying to get it perfect. I just let my bikes run loud and proud with the baffle out.
    Big Red.
  20. Cali-Rider

    Cali-Rider Member

    My only concern is that the piston skirt might ride on that wall of the cylinder. If it does come that low, you could be asking for big problems... A new cylinder is only $20, a new motor is $120... I know what I'd do.