ii reckon you will take the head and barrel off and the sides of the piston will be grooved up and blackened with carbon and the barrel will have some nice sores down it to match.your lucky as if it was a 50cc one it has a nickel plated bore and the 100cc doesnt.if and when you do get it rebored and get an pversized piston make sure you add a bit of 2 stroke oil to the petrol and mix it up about 25ml per litre of petrol,then run it and make sure the oil pump is working ad is bled as its a good chance the oil delivery is not sufficient if it has done this unless of course its due to a broken ring or main or big end bearing breaking up.look for any debris stuck in the top of the piston to give you a clue and see if it sounds rough if you turn it over gently with the piston off the rod.
adam bike doctor, May 2010
