Description
This NCY big-bore cylinder kit is the displacement upgrade for compatible 139QMB / QMB139 four-stroke scooters, taking the original 50cc platform to 81cc with a 50mm bore and the standard crankshaft stroke. Give your scooter more go with a cast-iron cylinder and matching piston assembly built for your next performance project. This is a big-bore conversion, not a standard-bore replacement, and the cylinder head is not included. No case cutting required!
Features
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More Displacement: A 50mm bore produces 81cc using the standard stroke, without requiring a stroker crankshaft to achieve that displacement.
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139QMB Performance Upgrade: A bolt-on cylinder upgrade for matching GY6 50 / 139QMB four-stroke builds.
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Cast-Iron Cylinder: Replacement cylinder with cooling fins for the air-cooled engine.
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Matched Piston Components: Includes piston, piston rings, wrist pin and retaining clips.
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Gasket Set Included: Head and base gaskets accompany the cylinder and piston components.
Specifications
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Brand: NCY
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Part number: 1100-1237
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Manufacturer part number: 603C02GY650
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Kit type: Big-bore cylinder conversion
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Engine platform: 139QMB / QMB139, GY6 50 four-stroke
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Bore: 50mm
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Displacement: 81cc with standard stroke
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Cylinder: Cast iron, air-cooled
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Included: Cylinder, piston, rings, wrist pin, retaining clips, head gasket and base gasket
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Cylinder head: Not included
Model Fitment
- Compatible with 139QMB / QMB139 (GY6 50) four-stroke scooters being converted from the original 50cc configuration to a 50mm big-bore setup.
Head compatibility matters: Most stock cylinder heads will not fit this kit. The supplier recommends the NCY 50mm big-valve performance cylinder head, 1100-1239, sold separately. Confirm the installed engine configuration and matching head before assembly.
Recommended Performance Pairings
Pair the kit with the NCY Performance Camshaft, 1100-1250, sold separately, to help the bigger cylinder reach its full performance potential. The original performance pairing targets 50–55 MPH; actual speed depends on the complete engine, tuning, gearing, rider load and riding conditions, rather than the cylinder kit alone.
The supplier recommends the NCY Oil Decompression Tube Assembly, 1100-1282, sold separately. It replaces the dipstick and allows excess crankcase pressure to be released, making it a useful companion to a cylinder-kit upgrade.
Not legal for use in California on pollution-controlled vehicles. Check local laws before installing.
This product is intended for off-road use only. This product is not intended for use on public roads or land.
Product Diagrams
