This is a complete 171cc big bore kit. It slips right in without any case boring.
Cylinder Kit:NCY GY6 150 61mm Cylinder Kit w/o head 62.9mm outer sleeve diameter.Give your GY6 based scooter some serious power with this bolt on 171.3cc kit for most GY6 125/150cc engines. As far as we know, this is the only 61mm cylinder kit for the GY6 engine that exists in the US. With most 61mm cylinder kits, you have to cut the engine cases in some way to make it fit (Outer Cylinder Skirt Diameter: 65mm). Not so with this kit (Outer Cylinder Skirt Diameter: 62.9mm). It also has a light weight cut-down piston to increase performance even more. It’s highly recommended to jet this kit significantly rich because of its high performance capability. To maximize performance and efficiency, it’s recommended to get our 61mm big valve head as well. Some stock heads may not fit.Have a look at our Decompression Tube Assembly, which replaces your dipstick and allows excess crank case pressure to be released. It’s a good idea to install one of these alongside any cylinder kit upgrade.Brand: NCYFits: GenuineGY6 125/150ccSize: 62.9mm Outer Cylinder Skirt Diameter
 
Camshaft: Performance Camshaft designed specifically for the GY6 Engine. This cam is ideal for increasing low end power. With its increased leading slope and later intake valve opening makes this the perfect upgrade to go along with your larger displacement cylinder, big valve head, or performance exhaust. Intake Lobe 26.25mm Exhaust Lobe 26.15mm
 
Cylinder Head: Valve Size: Intake-27.5, Exhaust-23.5This head will allow your cylinder to breathe better! Works great with our 61mm cylinder assembly. See below for dyno results.And you're wondering how can this get even better, right? Check out these Stainless Steel racing Valves to go with your new top end.When changing a cylinder kit or an exhaust, it's a good idea to pick up a few extra 8mm Studs, since these can easily need replacing and bring your project to a grinding halt while you wait.These nuts are essential. The smaller, 10mm diameter head allows for extra clearance between your wrench and the head for easy access.Standard 8mm thread diameter.
 
Gasket Set: Complete engine gasket set for the 61mm.
 
**PRICE INCLUDES FREE SHIPPING TO YOUR FRONT DOOR**
 
CM1100-1288,CM1100-1011,CM1100-1254,CM1100-1277