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Motorized Bicycle Trouble Shooting Use this area to post problems that may arise, if you could use some help in figuring out what is wrong with your engine and what needs to be done to achieve top performance.

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  #1  
Old 10-27-2016, 11:23 AM
Bzura Bzura is offline
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Default What's the cause? - hole in piston

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
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Old 10-27-2016, 12:21 PM
crassius crassius is offline
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Default Re: What's the cause? - hole in piston

since it is hard to get timing wrong in these, I'd have to guess 'way too lean' without any other info
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Old 10-27-2016, 12:44 PM
Bzura Bzura is offline
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Default Re: What's the cause? - hole in piston

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.
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Old 10-27-2016, 01:27 PM
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bairdco bairdco is offline
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Default Re: What's the cause? - hole in piston

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.
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Old 10-27-2016, 03:13 PM
crassius crassius is offline
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Default Re: What's the cause? - hole in piston

lack of oil will usually seize a piston well before a hole appears
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Old 10-27-2016, 05:28 PM
Bzura Bzura is offline
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Default Re: What's the cause? - hole in piston

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!"
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Old 10-27-2016, 07:57 PM
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Agreen Agreen is offline
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Default Re: What's the cause? - hole in piston

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?
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Old 10-27-2016, 11:27 PM
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Venice Motor Bikes Venice Motor Bikes is offline
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Default Re: What's the cause? - hole in piston

Way too lean!!

(No oil mixed in the gas wouldn't do that).
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Old 10-28-2016, 12:25 PM
crassius crassius is offline
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Default Re: What's the cause? - hole in piston

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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