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 23mm intake and 20mm exhaust valves for improved flow
• Short Valve Stem Design — replaces cylinder heads with 64mm short-style valve stems
• Precision Porting — 20.8mm intake port and 18.7mm exhaust port for optimized airflow

Specifications

• Cylinder Bore: 52.4mm
• Cylinder Sleeve OD: 54.4mm
• Wrist Pin Diameter: 13mm
• Total Piston Height: 36.3mm
• Compression Height: 20mm
• Intake Valve: 23mm
• Exhaust Valve: 20mm
• Intake Port: 20.8mm
• Exhaust Port: 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
• You may need to modify your engine case to accommodate the larger cylinder
• Replaces cylinder heads with 64mm short-style valve stems only

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

California Prop 65 Warning: www.p65warnings.ca.gov

• Increases displacement to 89.3cc (stock stroke) or 94.9cc (44mm stroker)
• Racing-grade non-emissions head with 23mm intake / 20mm exhaust valves
• Precision porting: 20.8mm intake port, 18.7mm exhaust port
• Complete kit — cylinder, piston, rings, head, and gaskets included
• 64mm short-style valve stem design

Bore: 52.4mm | Sleeve OD: 54.4mm | Wrist Pin: 13mm | Piston Height: 36.3mm | Compression Height: 20mm | Intake Valve: 23mm | Exhaust Valve: 20mm | Intake Port: 20.8mm | Exhaust Port: 18.7mm | Valve Stem: 64mm short | Displacement: 89.3cc (stock) / 94.9cc (44mm stroker) | SKU: 137-4

QMB139 / 139QMB 49cc/50cc 4-stroke engines. May require engine case modification to accommodate larger cylinder. Replaces 64mm short-style valve stem heads only. Off-road use only.