Oil pump crankshaft 16 teeth for GY6 50ccm 139QMB/QMA 2 different shafts are used in the 139QMB/QMA engines. They differ only in the drive part for the oil pump. The teeth on the shaft can have 16 or 22 teeth. there are also 2 different types of oil pumps for this. The oil pump shown here is used on 16 tooth shafts.