Seized Engine

Discussion in 'Motorized Bicycle General Discussion' started by tomcfitz, Mar 3, 2014.

  1. tomcfitz

    tomcfitz New Member

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    So my piston went bad, and I replaced it, however, when putting the new one in, I broke a piston ring, and I think a piece of it must have fallen into the crank case, as after running for a second, the engine seized completely.

    What's the best way to fix this?
     
  2. Greg58

    Greg58 Well-Known Member

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    Sorry to hear that, I would remove the engine then remove the cylinder and piston and wash out the crankcase with safety solvent or premixed fuel. I place a towel over a catch bucket and pour out the cleaning fluid through the towel catching the debris. In the future if you are removing the cylinder from a engine that you think has broke rings first raise the cylinder enough to get a shop rag under it and cover the openings into the crankcase, this will keep broken ring parts from falling in the engine. I learned that the hard way back in the motocross days. Did you replace the complete top end or just the piston? If the cylinder was scared by the first piston that could be why it locked up. Check the connecting rod to make sure it is not damaged or bent.
     
  3. tomcfitz

    tomcfitz New Member

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    I'm pretty sure the only reason it's seized is because the broken piece is stuck somewhere in the crankcase... how should i go about removing the broken piece?

    and yes, I replaced the whole top end.
     
  4. Greg58

    Greg58 Well-Known Member

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    Its not hard to totally disassemble the engine, the gear tool that comes with most kits and a couple of wrench and sockets and screw drivers is all it takes. A air wrench will make it easier. The link below will help.

    http://motorbicycling.com/showthread.php?t=391
     
  5. Kioshk

    Kioshk Active Member

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    Hey Fitz,

    I had this happen to me more than I want to admit when I started with the China Girls. I got lazy and used a small earth-magnet on the end of a string to retrieve ring pieces and needle-bearing pieces (they're magnetic), but this won't help with any aluminum chunks if there's port-skirt damage. There's also no guarantee that you'll get everything out since stuff can get stuck in the bearings and other hiding places. I have even filled the crankcase with gas and churned it with the flywheel...then dumped the fluid in hopes of clearing out any loose debris. It worked twice, failed once. I haven't had any problems with my build for a LOOOOONG time now, so I haven't had to even pull the head off in a few months. What you SHOULD do, and what I did the last time I had an issue is split the case and clean it out with premix. This is a great way to familiarize yourself with the engine, and will also give you the opportunity to make sure it's assembled properly; you may find that some things weren't installed as carefully as you'd like when the engine was born in China.

    So, sorry to be pessimistic, but you should expect that since your engine seized, the top-end is damaged; almost invariably in your situation, the loose ring piece is drawn up one of the the transfer-ports and gets jammed beween the piston-head and the cylinder wall ruining rings and the jug (although I had the opposite occur, and the cylinder wall was damaged BELOW the combustion-chamber). I have in desperation and cheapness replaced only the rings after a failure. If the cylinder gouging is minor, you can actually get by although your compression will be effected, you'll just need to dremel away some of the raised areas on the piston/jug, and even out the ring-lands. Even a really badly damaged piston can sometimes be resurrected if the pins are still good. In any case, you'll need to remove that head to see what's up, AND you may need to force it off.
     

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