1998 CR250 Power Valve Movement and Noise

[winchcable]

Hello,

I have a 1998 CR250, when it is running there is a loud noise, I can't pinpoint its location but it is in the engine area. I did the screwdriver to the ear trick and that doesn't help. I pulled the pipe off and cranked the engine so the piston was at the bottom of the exhaust port and felt the power valve. I can move it by hand very easilly up and down maybe a quarter of an inch. Can this be the noise I hear? The sound does sound kind of like a hollow aluminum on aluminum thunk. The sound follows the RPMs. Pulling in the clutch lever does nothing to the sound. When the bike is running can the piston and exhaust be moving that power valve with enough force to make that kind of raquet (sp)? It kind of sounds the same but I can't be sure. I have not taken the engine apart to check for play in the rod or piston. I have taken the ignition cover off and tried to move the flywheel and that is solid as a rock in all directions, no play at all.

So I guess the questions I have are:
Is the noise I am hearing normal?
Is the power valve supposed to move this much and this free (no effort at all to move by hand)?
Is the noise the power valve fluttering up and down because of the motion of the piston (there are no contact marks on the piston itself)?

Thanks.

 

[uts]

You say there are no marks on the piston but you have not taken the engine apart. Thge piston may be hitting the power valves. Remove the power valve cover on the lh side of the cylinder and start the bike. You will then see if the power valve is rattling up and down with the motion of the piston.