Naraku 139GMB 52.4mm Big Bore Cylinder & Head Kit | 89.3cc

Unlock serious performance gains with the Naraku QMB139 52.4mm Big Bore Cylinder & Head Kit. Engineered for QMB139 4-stroke 50cc engines, this complete kit bumps displacement to 89.3cc with a stock 41.4mm stroke — or all the way to 94.9cc when paired with a 44mm stroker crank. Everything you need for the swap is included.

What's Included

• Cylinder (52.4mm bore)
• Piston, rings, piston pin & circlips
• Cylinder head
• Head gasket & base gasket

Key Features

• Big Bore Upgrade: Increases displacement from 50cc to 89.3cc (stock stroke) or 94.9cc (44mm stroker crank).
• Racing-Grade Head: Non-emissions style head with larger intake (23mm) and exhaust (20mm) valves for improved flow.
• Short Valve Stem Design: Replaces cylinder heads with 64mm short-style valve stems. See related items if you need 64mm valves separately.
• Precision Porting: 20.8mm intake port and 18.7mm exhaust port for optimized airflow.

Technical Specifications

• Cylinder Bore: 52.4mm
• Cylinder Sleeve Outer Diameter: 54.4mm
• Wrist Pin Diameter: 13mm
• Total Piston Height: 36.3mm
• Compression Height: 20mm (center of wrist pin to top of piston)
• Intake Valve: 23mm
• Exhaust Valve: 20mm
• Intake Port Diameter: 20.8mm
• Exhaust Port Diameter: 18.7mm
• Valve Stem Length: 64mm (short style)
• Displacement (stock stroke): 89.3cc
• Displacement (44mm stroker): 94.9cc
• Compatible Engine: QMB139 49cc/50cc 4-stroke
• SKU: 137-4

Fitment Notes

• Compatible with 139QMB 50cc/49cc engines and various unlisted makes/models.
• You may need to modify your engine case to accommodate the larger cylinder.
• Replaces cylinder heads with 64mm short-style valve stems only.

?? Off-Road Use Only: This product is not intended for use on public roads or land.

?? California Proposition 65 Warning: This product can expose you to chemicals including lead, carbon monoxide, and other engine combustion byproducts, which are known to the State of California to cause cancer, birth defects, or other reproductive harm. For more information, visit www.p65warnings.ca.gov.