Quote:
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.
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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