yes is the answer ,you need to get it rebored to the next oversize for isnstance 0.5mm and get a piston kit to match it.when i rebore a barrel i will only do it once i have the new piston in my hand as they do fluctuate on size very slightly from manufacturer.so if the barrel is worn or scored yes you need a rebore or the new piston will get damaged very quickly and cannot seal against the cylinder wall properly anyway.
adam bike doctor(of milton keynes motorcycle centre), February 2011
