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08-11-2014, 05:22 PM | #1 | |
Join Date: Mar 2013
Posts: 40
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Quote:
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 |
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08-11-2014, 07:12 PM | #2 |
Join Date: Oct 2008
Location: Hyde Park, NY
Posts: 1,075
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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.
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2008 Eagle Milano 150- 9,679 miles 2009 Honda Rebel 250- 10,434 miles 2009 CF Moto Fashion- 16,023 miles 2009 MC-114 50cc Cub Clone- 4,317 miles twowheeler.yolasite.com/ That's 30,049 China Scootin miles and Counting. |
08-19-2014, 09:28 AM | #3 | |
Join Date: Apr 2006
Location: South Haven Michigan
Posts: 225
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Quote:
http://www.pencilgeek.org/2009/05/oc...nversions.html In regards to your valve to piston collision...I have seen this a few times in my Scooter parts/repair shop. It is caused by a stretched timing chain and or a weak or defective chain tensioner. What happens is that the chain jumps or slips a few teeth on the Cam or Crankshaft gear...this causes it to jump valve timing so that the valve is open as the piston comes up. What appears as pitting or melting of the piston is actually just scarring from the broken metal pieces being scattered around... Just my 2 cents... I only work on Scooters for a living..so I may be wrong... Glenn |
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11-25-2014, 11:08 AM | #4 |
Join Date: Jun 2014
Location: north woods of WI
Posts: 1
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carasdad. I Agree completely, timing chain tension should be checked and adjusted as a maintenance item.
Last edited by Flint; 11-25-2014 at 11:18 AM. Reason: too wordy the first time |
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