Wow!! Unbelievable!!! You won't believe what just happened!!!

[James2132]

I was riding my scooter then all of a sudden there's this loud noise then scooter shuts off. When i took it Apart this is what I found. How did this happen?? http://postimg.org/image/szr413v9n/ http://postimg.org/image/wlnn5rwfx/

[Admin]

Image no worky. :(

[James2132]

[James2132]

[James2132]

OMFG my valve is actually stuck in my piston!

[cheapeto]

Oh yeah, thats harsh.

[James2132]

But why did this happen?

[blueboy5000]

Detonation most likely. What rpms do you regularly ride at?

[James2132]

Like 6500 rpms

[Houndguy]

Wow! Talk about a failure.

OK, a few things come to mind and I am sure that I am probably wrong. After all I'm a monkey with a gun when it comes to mechanical things. But I do know something about physics.

1) What type of fuel were you using? If a higher octane than normal the more "blast" you would have. That compression could have blown a seal and forced the piston into it's current position.

2) Just a bad seal, it gave. Although I think you would have had some sort of warning sign before it got that far.

3) Somehow more fuel than normal was forced into the chamber, the ignition spark hits that higher than normal fuel ratio and BLAM. Although this is more commonly called a backfire or misfire.

4) Bad parts to begin with (and most likely the answer). How old was the scoot? What model? How many miles? All that matters but if I were to bet money on it I would say you had a hairline crack that expanded over time. Of course, again, there should have been some sign to that.

Anyhow...monkey with a gun so who the hell knows.

[Houndguy]

So what was it?

[James2132]

I have no clue. I'm just gonna get a new cylinder, piston. And head. This is very strange. I've never of this happening before. My belt broke too. I guess when the motor locked up it broke thebelt

[James2132]

Oh and I enjoyed the 5 mile walk pushing the bike home! Lol

[Swordsman]

Originally Posted by Houndguy

1) What type of fuel were you using? If a higher octane than normal the more "blast" you would have. That compression could have blown a seal and forced the piston into it's current position.

I find this one extremely unlikely. Octane isn't increased in fuel grades for more power, it's increased to slow combustion so you don't get pre-detonation (aka spark knock or pinging) with more aggressive cam timing. Longer octane chains are slower to break down as they burn.

I suspect there was a valve clearance issue, maybe when it pulls the valve closed. If it got really tight, it might have popped the valve head off since they're not exactly quality materials. Isn't that the exhaust side? I know the exhaust valve on my Ural used to get tighter over time while my intake valve got looser. I assume it was from the heat.

Looks like there could be some wear around the break point also, but I have no idea how that would occur because I don't know how scooter valves are put together. Maybe that's just from it banging around inside the chamber before it battle-axed the piston.

~SM

[kz1000st]

The break is right at the spin weld. If you were only at 6,500 I suspect a bad weld. There's enough carbon to indicate a rich to normal burn. A defective valve is possible. Or the valve hung and got tagged.