{"product_id":"cylinder-kit-81cc-iron-gy6-49cc-qmb139-ncy-brand","title":"NCY 50mm Big-Bore Cylinder Kit - 139QMB 50cc to 81cc","description":"\u003ch2\u003eDescription\u003c\/h2\u003e\u003cp\u003eThis \u003cstrong\u003eNCY big-bore cylinder kit\u003c\/strong\u003e is the displacement upgrade for compatible 139QMB \/ QMB139 four-stroke scooters, taking the original 50cc platform to \u003cstrong\u003e81cc with a 50mm bore and the standard crankshaft stroke\u003c\/strong\u003e. 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!\u003c\/p\u003e\u003ch2\u003eFeatures\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eMore Displacement:\u003c\/strong\u003e A 50mm bore produces 81cc using the standard stroke, without requiring a stroker crankshaft to achieve that displacement.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e139QMB Performance Upgrade:\u003c\/strong\u003e A bolt-on cylinder upgrade for matching GY6 50 \/ 139QMB four-stroke builds.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eCast-Iron Cylinder:\u003c\/strong\u003e Replacement cylinder with cooling fins for the air-cooled engine.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eMatched Piston Components:\u003c\/strong\u003e Includes piston, piston rings, wrist pin and retaining clips.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eGasket Set Included:\u003c\/strong\u003e Head and base gaskets accompany the cylinder and piston components.\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eSpecifications\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eBrand:\u003c\/strong\u003e NCY\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003ePart number:\u003c\/strong\u003e 1100-1237\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eManufacturer part number:\u003c\/strong\u003e 603C02GY650\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eKit type:\u003c\/strong\u003e Big-bore cylinder conversion\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eEngine platform:\u003c\/strong\u003e 139QMB \/ QMB139, GY6 50 four-stroke\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eBore:\u003c\/strong\u003e 50mm\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eDisplacement:\u003c\/strong\u003e 81cc with standard stroke\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eCylinder:\u003c\/strong\u003e Cast iron, air-cooled\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eIncluded:\u003c\/strong\u003e Cylinder, piston, rings, wrist pin, retaining clips, head gasket and base gasket\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eCylinder head:\u003c\/strong\u003e Not included\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eModel Fitment\u003c\/h2\u003e\u003cul\u003e\u003cli\u003eCompatible with 139QMB \/ QMB139 (GY6 50) four-stroke scooters being converted from the original 50cc configuration to a 50mm big-bore setup.\u003c\/li\u003e\u003c\/ul\u003e\u003cp\u003e\u003cstrong\u003eHead compatibility matters:\u003c\/strong\u003e 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.\u003c\/p\u003e\u003ch3\u003eRecommended Performance Pairings\u003c\/h3\u003e\u003cp\u003ePair 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.\u003c\/p\u003e\u003cp\u003eThe 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.\u003c\/p\u003e\u003cp\u003eNot legal for use in California on pollution-controlled vehicles. Check local laws before installing.\u003c\/p\u003e\u003cp\u003eThis product is intended for off-road use only. This product is not intended for use on public roads or land.\u003c\/p\u003e\u003ch2\u003eProduct Diagrams\u003c\/h2\u003e\u003cul class=\"az-content-resources\"\u003e\u003cli\u003e\n\u003ca href=\"\/search?view=az-assembly\u0026amp;q=72\"\u003eGO MAX CYLINDER CRANKSHAFT\u003c\/a\u003e \u003cspan\u003eCallout 13\u003c\/span\u003e\n\u003c\/li\u003e\u003c\/ul\u003e","brand":"NCY","offers":[{"title":"Default Title","offer_id":67964554805569,"sku":"1100-1237","price":129.0,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/1011\/7785\/2225\/files\/1100-1237_81c9ea5e-2ef8-4198-b556-c5ba8ef1baa1.jpg?v=1792993066","url":"https:\/\/azscooterparts.com\/products\/cylinder-kit-81cc-iron-gy6-49cc-qmb139-ncy-brand","provider":"AZScooterParts","version":"1.0","type":"link"}