NCY GY 50/QMB139 47mm bore, Cast Iron, Cylinder Kit w/o head Our most popular big bore kit for the QMB139/GY6 50 scooter engine, this bolt on 72cc kit really performs nicely when you combo it with part # 1100-1250, NCY Performance Camshaft. Don’t forget to upjet! NOTE: Remove your valve from your scooter’s head and meaure the full length of the valve stem. Some scooters like Znen(Wolf Brand, GMW, Bintelli, etc), Kymco 50cc 4T(Agility), some newer TaoTao and other 50cc 4-stroke scooters may have valve stem length over 64mm. For these applications use #1100-1326 Rocker Arm assembly. Have a look at our Decompression Tube Assembly which replaces your dipstick and allows excess crank case pressure to be released. Good idea to install one of these alongside any cylinder kit upgrade.