Cracked/Broken Ring 06 YZ125

[Joe_Jet]

06 YZ 125 ring broke and seized the piston and cylinder. What are known causes for this?

[jvann13]

Did the ring brake and seize the piston or did the piston seize breaking the ring?

How many hours? Is it stock? With limited info I would guess it seized witch caused the ring to brake. Bike was running lean maybe? Was it colder than normal? The 125 is temperamental about jetting and temp. I know. I have been through a few cylinders.

[Greg Y]

what does the piston look like? most of the time I see broken rings from lack of oil, deto, or hooking a port after losing th locator pin.......and the ocasional backwards piston....lol

[Padgett]

If you look at the ring I bet its worn on the exhaust side and is paper thin in that area. If it is then you ran the rings to long. A ring hanging in a port is rare these days unless some port work was done and the edges didn't get chaffered. Heat seize will show scaring on the exhaust side of the cylinder and discoloration (dark lines). Lean fuel mix will have scaring on both sides. Lean jetting will have a gray look on the plug and head and the cylinder will scare al the way around, more scares on the top part of the cylinder. If it has one or two scares then look at the reed peddles, one may have chipped off and went into the cylinder. For those reading this thread and are doing a top end, I recommend checking your reed cage (for loose screws) and peddles (chips or not seating) every top end.