NCY GY6 50/QMB139 50mm bore Cast Iron Cylinder Kit w/o head. The perfect upgrade for most QMB139/GY6 50 scooters, this bolt-on 81cc kit will really give your scooter some go. It is recommended to get part number 1100-1239, 50mm big valve head as well, as most stock heads will not fit. In addition, we really recommend 1100-1250, NCY Performance Camshaft as an amazing complimentary item to this kit. It will allow the kit to perform to its maximum potential and go 50-55 MPH! Have a look at our Decompression Tube Assembly (1100-1282) which replaces your dipstick and allows excess crankcase pressure to be released. Good idea to install one of these alongside any cylinder kit upgrade.