From what Paynes Cycle has told me, the piston kits that they got from Wossner, are the proper main diameter for the 280 TXT, BUT the Diameter for the pin (holding to con rod) is 18mm.
My piston, and as far as I know, any TXT engine (non PRO) has 16mm Pin Diameter.
It makes no sense to me. I suppose I can myself call up Wossner and ask what the deal is.
Looking at the Wossner site, the piston they list for a 2001 TXT280 is: 8144DA They say it fits 1999-2011. It lists the pin as: WP033, which is an 18mm pin.
Something ain't jiving.
EDIT - Just got off the phone with Wossner. I was informed that they were the ones who did the OEM pistons for GasGas. I was told they have 2 different pin hole diameters. Unfortunately he was setting up for at a trade show, so couldn't get me all the info. Time for me to call up Paynes & make sure they don't mod a piston, but get the correct one.
EDIT 2 - Just to clarify, I have not seen a single thing in my hands. I called Paynes 3-4 weeks ago, and was told he had some Wossner pistons that were for the 280, but would work for my bike as the 270\280 cylinder castings were the same and the 270 could be bored to be cleaned up. Paynes finally got the cylinder back from boring\plating & when they were picking a new pin bearing for me, found that the piston pin diameter was too large. They said that all the porting & everything else was correct, but they wanted to verify some of the other stuff with my original piston, so they had me send that out (which I shipped out today).
I'll be calling them (Paynes) up to make sure they get the correct piston from Wossner & don't modify the wrong one.