EC 250 New bike rattle!

[justsam]

Hi guys, Must of been a good boy last year as Father Xmas got me a spanking new EC 250 The bike is fantastic, especially the bouncy bits, well happy!
But and its a big BUT, since the first time I started the engine in the garage I noticed quite an obvious top end rattle. I hoped it would be nothing and go away as the motor settled in, but no its got worse and worse. You can here it just idling, when you crack the throttle and when its loaded up on off the bottom end. Its done 12 hrs now and I showed it my local dealer who have spoken to Gas Gas and who in turn have said they will stand by it whatever it does, and to just keep using it...
But I can't run it like this and have stripped it down to inspect. Can't see anything obvious, piston is wearing quite nicely, barrel looks fine and piston-barrel both matched 'B' But with the rings removed, the piston placed in the barrel there is a small amount of play. Not like its floating about, but if you push the opposite skirts of the piston to either side, theres an obvious movement there!
So as I'm inexperienced with 2 stroke motors, my question is, how tight a fit should the piston be? Is a small amount of play normal? Is it tighter the better?
The dealer is getting some tolerances from the factory so off to measure it all up at the weekend but I'd like some more info!
Any help appreciated.
Sam

[djroggen]

Likely pv rattle. Typically 250s are less. Are all the small fasteners up front tight? Head mount tight? Sometimes even pipe mounts seem to make top end "noise"

[Jakobi]

The pipe will rattle in a big way if the o-rings are blown out, and the stock ones don't take long. PV will chatter and rattle a bit too. If it was piston slap you'd expect the noise to dull down as the bike comes up to temp.

While chasing, maybe pull flywheel cover and check for any play on the crank. Got any video?

[AZRickD]

My rattle went away when I took off the right side cover and adjusted-out the power valve slack. It was probably moving about 20% of it's travel just in slop.

A little twist and the rattle was gone and my bottom end torque increased.

[thumperflipper]

Agree with Jake, slap should improve when coming to operating temp. At -20 my gas truck sounds like a diesel until it warms up to operating temp.

Are you sure it's top end? Did you try a mechanic's stethoscope? One of those helped me isolate a bad clutch throwout bearing noise that made my 300 sound like a diesel truck.

Good advice above. Check PV play, pipe O rings, crank play on either side, PV flapper side to side play, woodruff keys on both sides, adequately torqued flywheel and clutch hub nut.

Here was a rattle that made me nearly have to go on medication before I found out what it was, but it was only on deceleration (dropping RPM):

http://www.youtube.com/watch?v=dI0fUUHaDjQ

http://www.youtube.com/watch?v=YGjVWAAuwBA

post a youtube video link of the noise if you can and try to find the loudest source with the mechanic stethoscope