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
if you had it re-bored a new over-sized piston kit with ring's will be supplied for the price you have been quoted
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