ec125 2013 melted piston
 

Hi I have a 2013 ec125 that I converted to a supermoto. And it was running grate but then I geared it down so it would go faster. After that I rode it for about 500 meters and then the piston was melted. Do anyone know if the gearing could have caused the piston to melt?

If you were traveling west to east you would be going faster wrt to the rotating planet. Not sure if that would require any gearing change.

It ran perfectly fine before I change the gearing and after that it ran fore about 5 min and then the piston and cylinder was gone.

Ok we'll start again.

So you geared it, I'm going to guess Up rather than down so it could achieve a higher speed before hitting top revs in 6th?

The gearing won't affect the engine. The air mixture or fuel type vs ignition timing (usually fixed) could cause detonation that rapidly destroy pistons.

But tell us about the usage. Were you screaming its guts out full throttle, or had you just closed throttle?

Remember. Every time you go fast and let off the throttle, with the clutch engaged, the motor is turning with the throttle closed. This means there's little lubrication in the cylinder.

And the marginal pilot jet becomes the primary supply of cooling fuel.

Lubrication damage will look different to detonation. Have you taken it apart yet?

Yes I have taken it apart. and the front of the piston is melted. And yes I meant that I geared it up. But I geared it a bit too high so the engine wasn't able to rev out at 6th gear. And before the gearing change it ran fine without any problems. So I have no idea what could have caused the piston to melt.
//John

So that's detonation for sure. Less likely to be timing or too hot a spark plug which tend to kill the centre. I'd say too lean jetting or airleak. The longer time under full load may have exposed a long standing issue.

Okay thanks for the help.
//John

Gearing it up would put more load on the engine and that can cause it to detonate if you have too much ignition timing and/or not enough fuel octane.