Broken Ring

[jacksoj]

I broke the top ring on my YZ250. It broke right in the middle of the exhaust port. Could the ring have been snagging on the powervalve or exhaust port? Should I look at anything in particular before putting a new piston and rings in? Thanks in advance.

 

[Peer Lovell]

The only way I can imagine a ring breaking is if the ring locating pin on the piston fell out and the ring was allowed to turn, and then hit the port.
If that's the case you'll need to look for damage on the cylinder wall.
Are all the pieces of the ring there? If you can account for all the pieces of the ring and the retaining pin on the piston, then you should be o.k.

 

[jacksoj]

The pin is fine. The ring broke into two peices which didn't fall out until I took off the cylinder. After looking at it in better light, there's a gouge in the cylinder just above the exhaust port and a score mark that extends past the sub-exhaust ports. The powervalve also has a pretty good sized nick in it right where the ring broke.

 

[va_yzrider]

Sounds like the power valve was extending into the cylinder. It has to be relieved 0.015" to be safe from contacting the ring. Has the cylinder ever been bored?

 

[jacksoj]

The cylinder has not been bored. It was only on it's second piston. There did seem to be a clunk coming from the cylinder when the powervalve would extend back toward the cylinder. It's possible the powervalve was making contact, although the only marks on the powervalve are where the ring broke.

 

[bclapham]

sounds to me like the best way around this problem will be an over bore kit. hopefully things arent damamged too much, since i remember the 2002 cyclinder is slightly thinner so you might have to stop at the 265 or 275cc kit. check the powervalve also, there have been several brakages on them. there was a thread a while back in basic Q+A repairs forum

 

[bclapham]

http://dirtrider.net/forums3/showthread.php?threadid=73695

 

[jacksoj]

Thanks for all the info. For now, I have a new cylinder and powervalve on order. I'm still contemplating whether to get the existing cylinder bored out and re-plated or not.

 

[bclapham]

it would have been cheaper than the new cylinder and PV. it would make a good spare also