Here is our 72cc cylinder kit for 50cc GY6 QMB139 engines from NCY The NCY GY 50/QMB139 47 mm bore, cast iron, cylinder kit without head is our most popular big bore kit for the QMB139/GY6 50 scooter engine 30 Day Warranty Description Here is our 72cc cylinder kit for 50cc GY6 QMB139 engines from NCY. The NCY GY 50/QMB139 47 mm bore, cast iron, cylinder kit without head is our most popular big bore kit for the QMB139/GY6 50 scooter engine. Unlike some other big bore cylinder kits, this one bolts right on. All in all, the 72cc kit really goes together relatively easily and does exactly what it is that you want it to do. Let Monster Scooter Parts be your source for NCY scooter parts and accessories. 1100-1247