Blew it up!

[ACMX]

Ring traps at about 7.50min in the video and at 8.50 you pull of the track. There was more than ample opportunity to pull safely off the track. As I said if you would have stopped the bike pushed it back to the pits and untrapped the ring sanded the piston you would have been out for the next race. The pick up on the cylinder is from running hard with a partialy trapped ring.

I didn't notice anything really wrong until 8:08 in the video. I pulled off at the first safe place to pull off after that point. What is a trapped ring?

[ACMX]

Anyways, the cylinder is on it's way to millenium, and I'm going to rebuild it using OEM. Should run better than it did before.

[2T Institute]

Ring traps at about 7.50min in the video and at 8.50 you pull of the track. There was more than ample opportunity to pull safely off the track. As I said if you would have stopped the bike pushed it back to the pits and untrapped the ring sanded the piston you would have been out for the next race. The pick up on the cylinder is from running hard with a partialy trapped ring.

I didn't notice anything really wrong until 8:08 in the video. I pulled off at the first safe place to pull off after that point. What is a trapped ring?

At 7.45 a comment is on the screen saying how bad the bike is going ? What's a trapped ring ..................have a look at the piston and what do you notice?
About 5 seconds after you noticed the engine going off, anywhere on the left was a good spot to safely pull off the circuit or at the end of the corner had a large run off area/carpark. You were not going fast at the time either.

Ruuning the bike after something is obviously wrong is what costs you big $$ not only in repairs, the money you spent to do the race meeting is also wasted.

[ACMX]

The fade with the clips at 7:52 is a time laps of two laps... the clip before it had nothing to do with it. When I was on the track at the time, I did not notice anything wrong until right before the finish line jump(around 8:15), I then decided to exit at the nearest safe place. There is a fence lining the entire track on that left side, not sure if you noticed it. At 8:26 you probably noticed there is a path off the track to my left, however I previously was yelled at for using that as an exit. I only noticed the bike running poorly previously when reviewing the footage... Hence the text at 7:45... I did not notice it much when I was riding. I did the safest thing possible for me and other riders around me.

Does a trapped piston ring just mean it's compressed? Because mine it compressed. Didn't know you could fix that.

[cnrcpla]

A trapped piston ring means the engine overheated and the ring got stuck in the groove.

[Coop]

I would just hone it.

I don't think you can hone it. Aren't the yz125's nikasil platted?

You are confusing hone with bore. A hone just cleans up the cylinder wall but boring actually removes enough material to make the bore larger. You can hone that cylinder, but not bore it unless you get it re-plated after.