What's the cause? - hole in piston

Discussion in 'Motorized Bicycle Trouble Shooting' started by Bzura, Oct 27, 2016.

  1. Bzura

    Bzura New Member

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    First off, this is not my engine. This pic is of the top of a piston that's seized in the cylinder of a rather new engine. The owner is wondering what happened.

    Without giving my opinion, can you please let me know what you think happened? And like I said, this is a pretty new engine.

    Thanks.
    Matt

    IMG_3213.JPG
     
  2. crassius

    crassius Well-Known Member

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    since it is hard to get timing wrong in these, I'd have to guess 'way too lean' without any other info
     
  3. Bzura

    Bzura New Member

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    No other info available at this point. It's a bone stock engine. NT carb with stock jet.

    My guess is that it was run for a while with an air leak - or little to no oil was mixed with gas.
     
  4. bairdco

    bairdco a guy who makes cool bikes

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    Ditto the above responses. I've also blown holes in pistons on race bikes from having the crank "stretch" and slamming into the plug.

    There were some engines that had two headgaskets for clearance, so that could be the cause if one was left out.

    But most likely, too lean. Or running straight gas with no oil.
     
  5. crassius

    crassius Well-Known Member

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    lack of oil will usually seize a piston well before a hole appears
     
  6. Bzura

    Bzura New Member

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    This happened on the first tank of gas. The cause was almost no oil. I just got the info from the guy, and it turns out he had no idea how 2 stroke engines work.

    I figured the picture may be educational for some people. Thanks for the insight from the other members. And always remember, "There's more than one way to blow a hole in your piston!"
     
  7. Agreen

    Agreen New Member

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    Sounds about right. The piston probably siezed against the cylinder wall and the crank forced the rod through the piston.

    Ever wonder why so many rotary-powered cars end up junked without body damage?
     
  8. Venice Motor Bikes

    Venice Motor Bikes Custom Builder / Dealer/Los Angeles

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    Way too lean!! :(

    (No oil mixed in the gas wouldn't do that).
     
  9. crassius

    crassius Well-Known Member

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    more likely a combination of problems all at same time - no oil, too much air

    I get at least one a month of guys with no oil, piston stuck , but often can be saved.
     

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