Piston Stuck

Discussion in 'Motorized Bicycle General Discussion' started by lowaus, May 23, 2014.

  1. mapbike

    mapbike Active Member

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    Lol.... what is broken on the other engines?

    If they're that easy to fix it makes me wonder why you bought the new engine....

    Not trying to be rude here at all, just trying to wrap my mind around all of this somehow....

    Map
     
  2. lowaus

    lowaus New Member

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    one of the engines was cracked from the bottom end since day one , It came cracked in the box, so the seller sent a replacement, which was fine before i went for a long holiday for 4 months and left it outside, so i installed the top end from the new one to the one left outside and i got it to run today, put for some reason it seems to have no power, literally won't go over 14 miles, any one know why, also their seems to be a tinging sound coming
     
    #22 lowaus, May 24, 2014
    Last edited: May 24, 2014
  3. Davezilla

    Davezilla New Member

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    If you just installed a new jug and piston it's not going to have the same power as before until it's run in for some time, usually about 2 or 3 tanks of fuel before it loosens up and starts to make more power, but it shouldn't be a total weekling during this break in time either... did you check the compression after you got it all back together?
    Also, this "tinging" sound you're talking about... does it do it all the time or under load? It could be detonation if you're using regular fuel instead of premium, or it could even be the piston hitting the head, and they also tend to get a tinny sound and lose power when overheated. the worst thing you can do to a new engine or new cylinder/piston is to run it too long without letting it cool down or try to run it full power for anything more than just a short burst.
    I would pull the head back off and inspect the top of the piston and the combustion chamber for the tell tale signs of piston to head contact, and with the piston at bottom dead center, check the inside of the bore for any scratches in the plating or chunks of missing plating. These cylinders are usually pretty rough right out of the box and one should at minimum chamfer all the ports to prevent ring snags or prevent the plating from chipping off at the port openings. I've seen plenty enough new cylinders that the plating extends past the port openings and this will cause it to begin to peel off.

    Now back to the piston to head contact thing I mentioned, it shouldn't happen normally but if the base gasket or head gasket is too thin or not being used, there is the possibility as well as simply putting a new jug on sometimes it needs a little extra shimming at the base as there is a chance that the seller replaced your engine with one that's not exactly the same or the engine in your bike has the 40mm stroke and he replaced it with a 38mm stroke engine so it's worthwhile to check your piston top and combustion chamber, as well as seeing how far up your piston is at top dead center.
    I've had this happen when I put my original piston in a new bottom end and had to shim the bottom end and bring the jug up by 1mm to prevent contact as well as get the proper squish clearance. These things need to be checked anytime you put a different cylinder on because these can be that different even from the same seller.
     
  4. mapbike

    mapbike Active Member

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    No way any of us could no what the soumd is, we could probably give you a dozen different possibilities and maybe one or two of them may be it but who knows what that would be honestly.

    I wish I could point you directly to the answers you need but it seems you just have problem on top of problem and dont really understand these engines enough to solve them, makes me feel a bit helpless on this end because I really want to help ya but just cant cigure out how.....lol
     
  5. Davezilla

    Davezilla New Member

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    I agree with you Map ... All we can do is speculate and throw out suggestions without more details..

    Lowraus, Do you have a way to shoot a video? or even post some pics? That would help immensely for us to point you in the right direction. You can shoot a video with your phone and upload it to youtube fairly easily if you got a late model android or I phone and I could show you how if you're interested. If you can't do the video, maybe take some pics and post on imageshack or photobucket and link them to your posts in here so we can see your engine or your parts.

    The more we know about the problem, the better help you'll get, there's a lot of talent in here who can easily get you back up and running and I'll help as much as I can as well but we need better details on the problem or problems so we can tell you the right fix.

    I hope you get it running again and it doesn't matter if it's me or another member, or a group of members in here that finds the problem and gives you the right advise, but the better and the more detailed you describe the problem, the easier it is for one of us to give you the right advise and help you get back up and running.
     
  6. lowaus

    lowaus New Member

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    Thanks for the help I've been getting previously. I did get my problems fixed, I enjoy working on these small engines as much as anybody else, I worked on my engine all day today to fix most of my problems, since i was a using a different cylinder head, the piston was hitting the cylinder head, i fixed it by changing the cylinder head to because the combustion chamber was a different size. Also while doing that i noticed really heavy deep scratches on cylinder where the head gasket goes, will be replacing that tomorrow. I noticed my exhaust was flush between the gaskets, will be straightening that out aswell. Tomorrow i will mix in new oil and change my filter, because it seems to separate the oil and petrol. I will be chaining the magneto because it is most likely water damaged from a while ago. So pretty much back to the basics
     
  7. CTripps

    CTripps Active Member

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    Glad you're getting it sorted out... the only thing i could add in would be to try to get some help from some of the other Aussie members, there may be one close enough to you to have a look.
     
  8. Davezilla

    Davezilla New Member

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    Very True... You should see if Theon lives somewhere close to you, he's got the experience and knows these things really really well.
     
  9. lowaus

    lowaus New Member

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    Hi so it found out the problem, it was with the cylinder, (pretty sure i ported it wrong). well It got running and back to around 26 miles per hour, and then It lost compression, It sounded like it did. So i got home and pulled the cylinder head out to find a huge crack on the head. i also noticed the head wasn't sandwiched between the gasket and cylinder. maybe because the acorn nut was to small. I got around that and replaced the head that but now it makes a cracking sound. I will upload a video soon.
     
    #29 lowaus, May 25, 2014
    Last edited: May 25, 2014
  10. lowaus

    lowaus New Member

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    #30 lowaus, May 25, 2014
    Last edited: May 25, 2014
  11. lowaus

    lowaus New Member

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    bump,bump,bump
     
  12. Kioshk

    Kioshk Active Member

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    I'm staying outta this one, but I MUST say that from your video, your drive-chain is rattling something ridiculous. There's either too much slack, or that engine's not mounted securely. Good luck, and wear your helmet.
     
  13. lowaus

    lowaus New Member

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    i noticed taking the end cap outta my muffler reduced the vibration. it was the vibrations causing the sound
     
  14. CTripps

    CTripps Active Member

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    Don't run without the end cap on the muffler for long.. it reduces back pressure (which 2-strokes rely on to cycle properly) and makes you loud as %^&* and annoys neighbours/draws law enforcement. The first will only affect you and your bike, the latter will have a trickle-down effect on anyone in your region who wants to ride.

    Legislation is written for those that draw (unwanted) attention.
     

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