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

[ragtopdodge]

This happened to me too! My Il Bello (150cc) had about 2500 miles on it. Ran great!

This totally sux.

[ragtopdodge]

Although in MY case, clearly the piston melted as well.

[rks]

Don't know caused these problems, or how scooters were operated/maintained....and of course, defective parts will cause catastrophic failure....however I feel that monitoring as much as possible, may catch an abnormal condition before something lets go.

So my scoot had it's speakers jerked out, and in the resulting holes, gauges were installed. Maybe not the best location for viewing while driving, but still more useful than speakers on a scooter.....and I would certainly notice high oil temps before melting the engine...Bob

[IMG][/IMG]

[ragtopdodge]

Not a bad idea.

[Swordsman]

Originally Posted by ragtopdodge

This happened to me too! My Il Bello (150cc) had about 2500 miles on it. Ran great!

This totally sux.

Ah, ye olde holy piston! Any time I've ever heard of this, it's been due to running lean. Possible reasons for lean condition: air leak, incorrect jetting, vacuum operated petcock for the fuel supply. At high RPMs, vacuum petcocks may not react quickly enough, starving the carb for gas and throwing your air/fuel ratio off. Older Urals are (in)famous for it.

(You may notice I reference Urals a lot. They require a lot of tinkering, so it's the bike I have the most mechanical experience with! )

[carasdad]

Originally Posted by Swordsman

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

TOTALLY agree!! and this is one of THE biggest misconceptions about high octane fuel! Folks believe higher octane = more power cause it burns faster. Yes Sir...you are correct..it burns slower as to prevent detonation in high compression engines. In my Scoots it actually decreases performance.. Folks say.. "But my manual says to use 91 octane or better" Here is where the confusion comes in.. Ya see..in European and Asian countries they use a different formula. They use RON only..which translates 91 octane in their gas to 87 octane in the U.S. where we use the (RON+MON)/2 formula. READ the little decal on your local gas station pump...it even says octane is based on (RON+MON)/2.. Here is a good link..a good read that should clear up the confusion on octane ratings that are posted so often on here. I have a 2003 Tank Urban Sporty 50 that has seen NOTHING but 87 for all of it's 21,200 miles so far. Whole engine is all original still...but is about due for rings..which is not bad for that much mileage. ok..the link..read and heed..
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

[cheapeto]

Great post Glen!!

[carasdad]

Originally Posted by cheapeto

Great post Glen!!

cheapeto you are very welcome. Ya see our junk 10 page owners manuals are written in Chinese..translated to English. Their 91 octane(by RON measurement only) equals our 87 octane. Only using American grade 91-93 octane premium gas has been argued here MANY times. But if you read the charts in the link..you will see it is not needed. The GY6 50 and 150 engines are NOT high compression racing engines(unless we build them that way)..so true American premium gas is not needed. Sure premium only costs a few cents more per tank full in our tiny 1-1 1/2 gallon tanks. But why use premium high octane to decrease the combustion rate of an already small displacement engine that needs all the help it can get to make power all ready? As for his engine damage..again that is NOT piston melting. In my shop I have seen that very same thing as shown in the pictures. To verify the cause we lined up the timing marks...pushed a piece of wire down the spark hole..and low and behold..the piston was NOT at TDC. The cam chain had jumped several teeth and the timing was WAY off. This of course caused the valve to 'kiss' the piston. The broken off metal parts bounced around in the engine as it continued its rotation while shutting down..and gave the illusion of a melted piston. Any of us that have welded or melted metal know that...when metal melts..it flows smoothly. It does NOT leave sharp edges and pitting. Like water it flows smoothly seeking its own level. Therefore what we see in the pics is mechanical damage and not heat related damage.. But then what do I know..I am a Paramedic..Cardiac Tech and Nurse..not an ASE certified mechanic... No longer in the Medical Field cause after 30 years of that I got burned out. I am also a disabled VET with 21 years service..so I am unable to work in the medical field anymore due to broken body parts and high toxin levels. Sooo...I opened my own Scooter parts/repair shop which has been a fun 9 years so far. But then when ya do something ya like doing..such as a hobby that you get paid to do...you never have to go to work right?
Glenn

[seamus26]

Originally Posted by carasdad

cheapeto you are very welcome. Ya see our junk 10 page owners manuals are written in Chinese..translated to English. Their 91 octane(by RON measurement only) equals our 87 octane. Only using American grade 91-93 octane premium gas has been argued here MANY times. But if you read the charts in the link..you will see it is not needed. The GY6 50 and 150 engines are NOT high compression racing engines(unless we build them that way)..so true American premium gas is not needed. Sure premium only costs a few cents more per tank full in our tiny 1-1 1/2 gallon tanks. But why use premium high octane to decrease the combustion rate of an already small displacement engine that needs all the help it can get to make power all ready? As for his engine damage..again that is NOT piston melting. In my shop I have seen that very same thing as shown in the pictures. To verify the cause we lined up the timing marks...pushed a piece of wire down the spark hole..and low and behold..the piston was NOT at TDC. The cam chain had jumped several teeth and the timing was WAY off. This of course caused the valve to 'kiss' the piston. The broken off metal parts bounced around in the engine as it continued its rotation while shutting down..and gave the illusion of a melted piston. Any of us that have welded or melted metal know that...when metal melts..it flows smoothly. It does NOT leave sharp edges and pitting. Like water it flows smoothly seeking its own level. Therefore what we see in the pics is mechanical damage and not heat related damage.. But then what do I know..I am a Paramedic..Cardiac Tech and Nurse..not an ASE certified mechanic... No longer in the Medical Field cause after 30 years of that I got burned out. I am also a disabled VET with 21 years service..so I am unable to work in the medical field anymore due to broken body parts and high toxin levels. Sooo...I opened my own Scooter parts/repair shop which has been a fun 9 years so far. But then when ya do something ya like doing..such as a hobby that you get paid to do...you never have to go to work right?
Glenn

Thank you for your service in many respects. Paramedics, firefighters ... you're all heroes in my book. And a scooter repair tech to boot.

Good post about octane. I've always understood octane to be resistance to ignition. My old Grand Wagoneer used to knock like crazy without premium.

I run a 150cc GY6 and I've been putting premium in it all along. In fact, if you've seen my other posts, I've kind of obsessed about it.

My question, I guess, is if higher octane means less pre-ignition, wouldn't that be a protection for your engine, especially at higher RPMs?

[carasdad]

Originally Posted by seamus26

Thank you for your service in many respects. Paramedics, firefighters ... you're all heroes in my book. And a scooter repair tech to boot.

Good post about octane. I've always understood octane to be resistance to ignition. My old Grand Wagoneer used to knock like crazy without premium.

I run a 150cc GY6 and I've been putting premium in it all along. In fact, if you've seen my other posts, I've kind of obsessed about it.

My question, I guess, is if higher octane means less pre-ignition, wouldn't that be a protection for your engine, especially at higher RPMs?

You are welcome! I would serve 21 more years if I wasn't in such bad health. Kidneys died due to chemicals we were exposed to. But of course the VA does stand behind those of us that were laden with toxins.. In fact they stand behind us... 0%..
In regards to high octane..well if ya don't have pre-ignition I wouldn't see a need for it. But if it works for ya..use it...only costs a few pennies more per tank. In my Scoot it just seems to give less power. I used to own a Turbo Charged PT Cruiser and it HAD to have high octane..otherwise it sounded like VW diesel engine going down the road.. I am not against high octane gas..I just wanted to let folks see and read that when their Asian manual says 91 octane..it is RON which equals 87 in U.S. gas. Cause many freak out or get frustrated when they can't find a gas station with 91 octane(U.S. grade gas)

[scootersparts.net]

Seems like defective valve to us!

[carasdad]

Originally Posted by scootersparts.net

Seems like defective valve to us!

Could be that as well. Valve tip just broke off. I was merely posting what I have seen and not saying it is the definitive problem.. But it is mechanical related and not heat or detonation related. As I am sure you know..molten/melted metal does not create sharp pitted areas such as in the pics..

[Maddog]

Classic "dropped valve" syndrome. Check to see If the valve retainer or keeper is still intact. Or is the valve spring broken? Somehow the retainers came loose and allowed the valve to "drop" and strike the piston until it snapped.

[cheapeto]

Hey Glen, when I first came to SD, like many I lurked for about a year before I registared, and ONE of the big fights going on back then (man I miss all that great info) was gas ratings and octane levels, and ethanol.
I always go do my own research for a thing, and man you nailed it!!

[kz1000st]

Just so you don't feel bad about this take a gander at what happens to the high priced spread. How would you like to spend that much money and have this happen.

http://modernvespa.com/forum/topic130381.2