NCY Big Valve Cylinder Head (61mm): 171cc High-Flow for GY6

Instant Displacement: The "No-Cut" 171cc Big Bore Kit

The NCY 61mm Cylinder Kit is the only 171cc upgrade available in the U.S. designed to fit without machining your engine cases. Featuring a specialized 62.9mm outer skirt, this aluminum cylinder drops directly into standard GY6 150cc blocks. It is the ultimate "weekend project" for riders demanding a massive jump in torque and acceleration without the need for professional machine shop services.

The NCY Performance Advantage

• True Bolt-On Engineering: Slim-skirt design eliminates the need to "split the cases" or grind the engine block for clearance.
• Advanced Thermal Cooling: All-aluminum construction dissipates heat significantly faster than stock cast-iron cylinders, preventing power fade during long-distance riding.
• High-RPM Piston: Includes a specialized "short-skirt" racing piston to reduce reciprocating mass, allowing for faster revving and higher top-end potential.

Comprehensive Fitment Guide

This kit fits 125cc and 150cc 4-stroke GY6 engines (B-Case) and specific Genuine Scooter Co. models:

Technical Specifications

• Displacement: 171.3cc (61mm Bore)
• Outer Skirt Diameter: 62.99mm (Direct Fit)
• Material: High-Grade Aluminum
• Kit Includes: Cylinder, Piston, Rings, Wrist Pin, Clips, and Performance Gaskets.
• SKU: 1100-1288

Note: Fueling Requirements
A big bore kit requires more fuel. You must upjet your carburetor (typically a #125 or #130 main jet) to prevent a lean condition. To reach the full power potential of 171cc, we highly recommend pairing this with the NCY Big Valve Head (SKU 1100-1254).

Pro Tip: 

• We recommend jetting this kit significantly richer due to its high-performance capabilities. To optimize both performance and efficiency, consider upgrading to our 61mm big valve head, as some stock heads may not be compatible.
• Have a look at our Decompression Tube Assembly, which replaces your dipstick and allows excess crankcase pressure to be released. It’s a good idea to install one of these alongside any cylinder kit upgrade.

Visit our NCY Performance Parts page to shop all performance upgrades available for your vehicle.

About NCY: NCY is the aftermarket performance parts leader for the most popular scooter brands, including Honda, Yamaha, Genuine, Vespa, SYM, Lance, KYMCO, and GY6 / QMB powered scooters. Made in Taiwan with strict quality standards since 1997, NCY is ISO 9001 certified.

Made in Taiwan.

This product is intended for off-road use only.

This product is not intended for use on public roads or land.

This product is not legal for use in California on pollution-controlled vehicles. Check local laws before installing.

*Performance upgrades are considered racing parts and are not covered by warranty.

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