Naraku GY6 63mm Big Bore Kit

Give your GY6 build more muscle with the Naraku 63 mm Forged Piston 180cc Big Bore Kit. Designed for compatible GY6 125cc and 150cc four-stroke starting engines, this kit increases displacement to approximately 180cc for a stronger foundation for torque and acceleration tuning. A finned cylinder, forged piston, piston rings, wrist pin, retaining clips and gaskets bring the core components together for your big-bore upgrade.

Crankcase modifications are required to install this cylinder kit. This is not a drop-in replacement. See our NCY Engine Case Boring Tool to get the job done.

Key Features

• 63 mm Big Bore: Increases displacement to approximately 180cc with the appropriate crankshaft stroke.
• Forged Piston: Performance piston supplied with rings, wrist pin and retaining clips.
• Finned Cylinder: External cooling fins help dissipate heat from the air-cooled engine.
• Included Gaskets: Cylinder head and base gaskets, along with additional sealing pieces, support assembly.
• Fitment Measurements: 64.9 mm outer sleeve diameter and 54 × 54 mm cylinder-stud spacing help identify the required engine configuration.

Technical Specifications

• Brand: Naraku
• Part number: 137-11
• Engine application: Compatible GY6 125cc / 150cc four-stroke starting engines; excludes QMK and 169cc engines
• Bore: 63 mm
• Resulting displacement: Approximately 180cc, depending on crankshaft stroke
• Outer sleeve diameter: 64.9 mm
• Overall cylinder height: 90 mm
• Wrist pin: 15 mm diameter × 48 mm length
• Cylinder-stud spacing: 54 × 54 mm center-to-center; approximately 76 mm diagonal
• Additional mounting dimensions: 63 mm across the lower holes; 41 mm between the right-side middle and lower holes
• Installation requirement: Crankcase modifications required

Compatibility

For compatible 125cc and 150cc starting engines only. Not compatible with QMK engines or 169cc starting engines.

Having “QM” or “FM” in the engine code does not automatically make an engine compatible. Match the mounting pattern, sleeve diameter, cylinder height and wrist-pin size, and confirm compatibility with your cylinder head and crankshaft. Plan for crankcase modifications and appropriate fuel-system tuning as part of the installation.

This product is intended for off-road use only. This product is not intended for use on public roads or land.

• 63 mm bore for approximately 180cc resulting displacement, depending on crankshaft stroke
• Forged piston with rings, 15 × 48 mm wrist pin and retaining clips
• Finned air-cooled cylinder with included gaskets
• 54 × 54 mm cylinder-stud spacing; approximately 76 mm diagonal
• For compatible GY6-A 125cc/150cc starting engines only; excludes QMK and 169cc engines
• Crankcase modifications required; off-road use only

Brand: Naraku; Part number: 137-11; Application: compatible GY6-A 125cc/150cc four-stroke starting engines; Bore: 63 mm; Resulting displacement: approximately 180cc depending on stroke; Outer sleeve diameter: 64.9 mm; Overall cylinder height: 90 mm; Wrist pin: 15 mm diameter × 48 mm length; Cylinder-stud spacing: 54 × 54 mm, approximately 76 mm diagonal; Additional mounting dimensions: 63 mm lower-hole spacing, 41 mm right-side middle-to-lower spacing; Piston: forged; Crankcase modifications required; Excludes QMK and 169cc starting engines; Off-road use only

Compatible GY6-A 125cc/150cc four-stroke starting engines only: 157QMJ, 152QMI, YN1P57QMJ, JJ157QMJ, 1P57QMJ, BN157QMJ; compatible 1P52FMI, 154FMI and other QMI/QMJ configurations with matching dimensions; does not fit QMK engines or 169cc starting engines; confirm 54 × 54 mm stud spacing, 15 mm wrist pin, cylinder height and sleeve clearance; crankcase modifications required