Scooterworks Exclusive Custom Big Bore Engine Cases for GY6 150 Long Engine.  We machine these in matched pairs ourselves!  They are bored to fit up to a 63mm Performance Cylinder Kit.   Go big. 
Cases are matched Right side and Left side, and stamped with a serial number to make sure you have a perfectly matched set.  
Check out the following Cylinder Kits that will work with these cases on a GY6 150 Engine: 
57.4mm Cast Iron 
59mm Cast Iron 
61mm Cast Iron 
63mm Cast Iron 
58.5mm Ceramic 
61mm Ceramic 
62mm Ceramic 
Pick up a new crankcase gasket to go with your new, big bore cases.
Special Bore (Sold in Matched Pair)    
Not legal for use in California on pollution controlled vehicles.  Check local laws before installing.