Compatible with 50cc GY6 139QMB engines High performance part For use with NCY 81cc cylinder kits Great for custom projects This is our high performance 50 mm cylinder head by NCY The 50 mm cylinder head is for use with NCY 81cc cylinder kits, and is compatible with 50cc GY6 139QMB engines 30 Day Warranty Description This is our high performance 50 mm cylinder head by NCY. The 50 mm cylinder head is for use with NCY 81cc cylinder kits, and is compatible with 50cc GY6 139QMB engines. Let Monster Scooter Parts be your source for NCY scooter parts and accessories. 1100-1239