What could cause the piston to hit the powervalve?

[shaft]

I have a 95 CR125 and 2 years ago the piston in my bike hit the powervalve taking a chunk out of the top of the piston down to the ring grove.I had my local bike shop inspect the cylinder they said everything was fine and I just replaced the piston.Now 2 years and 4 topends later it happened again with only 3 hours on the piston.what could be my problem and how do I fix it?

 

[MRKRacing125]

Sounds like timing could be off with the powervalves or the specs. on the powervalves are not right.... any adjustments can you make?

 

[agent 86]

Just got my sons RM back from the shop. The mechanic had to fix the washer that holds the valve down. He told me it could hit the piston. Hope this helps

 

[Durt Cycler]

There should be a clip on the end of the powervavle to prevent it from going in the cylinder bore. If this clip comes loose and comes off hte powervavle somehow it will allow the powervavle to hit the piston. I've done prenty of work time on my CR125 topend ('95 ported cylinder now) to know how everything works so if you need help just let me know or give me a PM.

 

[Peer Lovell]

On a '95 the only thing I can think of is installing the power valve flapper upside down. There is a ridge on one side of the flapper valve. The valve must be installed so the ride is on the top.
Other than that, if the two rods that act guides for the valve are installed correctly, there is no way the flapper can move up against the piston.

Have there been any modifications made to the cylinder head?

 

[Durt Cycler]

Only thing else I can think of is the cylinder bore was worn and there was no clearance from the vavles and the bore so the piston made contact with the powervavle.....?

 

[Peer Lovell]

For that to happen, the cylinder bore would have to be so worn the bike wouldn't even start, let alone run.

How about the small hole in the valve flapper ( that's the one closest to the exhaust ). Is this hole elongated or enlarged, or are the rod's bent?

 

[Durt Cycler]

Originally posted by Peer Lovell
For that to happen, the cylinder bore would have to be so worn the bike wouldn't even start, let alone run.

Opps didn't even think of that...Sorry for my last reply.:ugg:

 

[KDX220rm]

I had an 89 RM250 that the piston hit the powervalve. DurtCycler was right, the circlip came loose and let the powervalve move around and the piston hit it.