{"product_id":"naraku-524mm-performance-cylinder-head-kit","title":"Naraku 52.4mm Big Bore Kit 89cc - 139QMB 50cc GY6 Scooters","description":"\u003cp\u003eThis \u003cstrong\u003eNaraku 52.4mm Big Bore Cylinder \u0026amp; Head Kit\u003c\/strong\u003e (SKU 137-4) is a complete top-end upgrade for 139QMB (QMB139) 50cc 4-stroke scooters, the Chinese GY6 50cc platform based on Honda's GY6 design. It bumps displacement to \u003cstrong\u003e89.3cc\u003c\/strong\u003e on the stock 41.4mm stroke, or \u003cstrong\u003e94.9cc\u003c\/strong\u003e with a 44mm stroker crank. The kit includes a ready-to-bolt-on head with larger valves, so you get a real jump in power and acceleration over a stock 50cc.\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\u003ch3\u003eWhat's Included\u003c\/h3\u003e\u003cul\u003e\n\u003cli\u003e52.4mm cylinder\u003c\/li\u003e\n\u003cli\u003eNaraku piston with rings, wrist pin, and circlips\u003c\/li\u003e\n\u003cli\u003eCylinder head with valves and springs installed\u003c\/li\u003e\n\u003cli\u003eGasket set, including head, base, and exhaust gaskets\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eFeatures\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eBig bore upgrade:\u003c\/strong\u003e 50cc to 89.3cc (stock stroke) or 94.9cc (44mm stroker crank).\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003ePerformance head:\u003c\/strong\u003e Non-emissions design with larger 23mm intake and 20mm exhaust valves.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eImproved flow:\u003c\/strong\u003e 20.8mm intake port and 18.7mm exhaust port.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eComplete kit:\u003c\/strong\u003e Everything needed for the top-end swap in one box.\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eSpecifications\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003ePart number:\u003c\/strong\u003e 137-4\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eCylinder bore:\u003c\/strong\u003e 52.4mm\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eCylinder sleeve OD:\u003c\/strong\u003e 54.4mm\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eWrist pin diameter:\u003c\/strong\u003e 13mm\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eTotal piston height:\u003c\/strong\u003e 36.3mm\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eCompression height:\u003c\/strong\u003e 20mm\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eIntake valve:\u003c\/strong\u003e 23mm\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eExhaust valve:\u003c\/strong\u003e 20mm\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eIntake port:\u003c\/strong\u003e 20.8mm\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eExhaust port:\u003c\/strong\u003e 18.7mm\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eValve stem length:\u003c\/strong\u003e 64mm (short style)\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eDisplacement:\u003c\/strong\u003e 89.3cc (41.4mm stock stroke) \/ 94.9cc (44mm stroker)\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eBrand:\u003c\/strong\u003e Naraku\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eModel Fitment\u003c\/h2\u003e\u003ctable\u003e\u003ctbody\u003e\n\u003ctr\u003e\n\u003cth\u003eEngine\u003c\/th\u003e\n\u003cth\u003eEngine Codes\u003c\/th\u003e\n\u003cth\u003eNotes\u003c\/th\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eGY6 50cc 4-stroke\u003c\/td\u003e\n\u003ctd\u003e139QMB, QMB139\u003c\/td\u003e\n\u003ctd\u003eEngines with the 64mm short-valve head\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\u003c\/table\u003e\u003cp\u003e \u003c\/p\u003e\u003cp\u003eCheck the engine code stamped on your engine case before ordering. Engines marked 139QMB may use this kit, but confirm your original head uses 64mm short-style valves. The 52.4mm sleeve may require machining the engine case for clearance.\u003c\/p\u003e\u003ch3\u003eInstallation Notes\u003c\/h3\u003e\u003cp\u003eA big bore kit adds fuel and airflow demand. Plan to rejet or upgrade your carburetor and retune your variator rollers and clutch springs for the best results.\u003c\/p\u003e","brand":"Naraku","offers":[{"title":"Default Title","offer_id":67964511617345,"sku":"137-4","price":300.0,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/1011\/7785\/2225\/files\/450236.jpg?v=1792945394","url":"https:\/\/azscooterparts.com\/products\/naraku-524mm-performance-cylinder-head-kit","provider":"AZScooterParts","version":"1.0","type":"link"}