61mm Aluminum Drop in cylinder kit for 125cc and 150cc GY6 engines, commonly referred to as a 171cc kit. In most cases, no special tools are needed for the job and no engine case machining is required! Old style GY6 engines may still require case machining, please see Specifications tab. Includes a light weight 3.6 ounce machined piston. When used with a 57.8mm stock stroke crankshaft you get an honest 168.9cc displacement. It is recommended to pair this kit with a 61mm head and upjet your stock carb or upgrade to a larger carb. This cylinder is .5mm shorter than standard GY6 cylinders. A second base gasket or spacer may be necessary if there is too much slack in the cam chain. Made in Taiwan! Please Note: Not for use with a stroker crank! Please see our Warranty Returns Policy.