{"product_id":"naraku-qmb139-52-4mm-performance-cylinder-head-kit-137-4","title":"Naraku 139GMB 52.4mm Big Bore Cylinder \u0026 Head Kit | 89.3cc","description":"\u003cp\u003eUnlock serious performance gains with the \u003cstrong\u003eNaraku QMB139 52.4mm Big Bore Cylinder \u0026amp; Head Kit\u003c\/strong\u003e. Engineered for QMB139 4-stroke 50cc engines, this complete kit bumps displacement to \u003cstrong\u003e89.3cc\u003c\/strong\u003e with a stock 41.4mm stroke — or all the way to \u003cstrong\u003e94.9cc\u003c\/strong\u003e when paired with a 44mm stroker crank. Everything you need for the swap is included.\u003c\/p\u003e\u003ch3\u003eWhat's Included\u003c\/h3\u003e\u003cul\u003e\n\u003cli\u003eCylinder (52.4mm bore)\u003c\/li\u003e\n\u003cli\u003ePiston, rings, piston pin \u0026amp; circlips\u003c\/li\u003e\n\u003cli\u003eCylinder head\u003c\/li\u003e\n\u003cli\u003eHead gasket \u0026amp; base gasket\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch3\u003eKey Features\u003c\/h3\u003e\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eBig Bore Upgrade:\u003c\/strong\u003e Increases displacement from 50cc to 89.3cc (stock stroke) or 94.9cc (44mm stroker crank).\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eRacing-Grade Head:\u003c\/strong\u003e Non-emissions style head with larger intake (23mm) and exhaust (20mm) valves for improved flow.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eShort Valve Stem Design:\u003c\/strong\u003e Replaces cylinder heads with 64mm short-style valve stems. See related items if you need 64mm valves separately.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003ePrecision Porting:\u003c\/strong\u003e 20.8mm intake port and 18.7mm exhaust port for optimized airflow.\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch3\u003eTechnical Specifications\u003c\/h3\u003e\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eCylinder Bore:\u003c\/strong\u003e 52.4mm\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eCylinder Sleeve Outer Diameter:\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 (center of wrist pin to top of piston)\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 Diameter:\u003c\/strong\u003e 20.8mm\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eExhaust Port Diameter:\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 (stock stroke):\u003c\/strong\u003e 89.3cc\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eDisplacement (44mm stroker):\u003c\/strong\u003e 94.9cc\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eCompatible Engine:\u003c\/strong\u003e QMB139 49cc\/50cc 4-stroke\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eSKU:\u003c\/strong\u003e 137-4\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch3\u003eFitment Notes\u003c\/h3\u003e\u003cul\u003e\n\u003cli\u003eCompatible with 139QMB 50cc\/49cc engines and various unlisted makes\/models.\u003c\/li\u003e\n\u003cli\u003eYou may need to modify your engine case to accommodate the larger cylinder.\u003c\/li\u003e\n\u003cli\u003eReplaces cylinder heads with 64mm short-style valve stems only.\u003c\/li\u003e\n\u003c\/ul\u003e\u003cblockquote\u003e\n\u003cstrong\u003e?? Off-Road Use Only:\u003c\/strong\u003e This product is not intended for use on public roads or land.\u003c\/blockquote\u003e\u003chr\u003e\u003cp\u003e\u003cstrong\u003e?? California Proposition 65 Warning:\u003c\/strong\u003e 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 \u003ca href=\"https:\/\/www.p65warnings.ca.gov\" target=\"_blank\"\u003ewww.p65warnings.ca.gov\u003c\/a\u003e.\u003c\/p\u003e","brand":"Naraku","offers":[{"title":"Default Title","offer_id":48112280076475,"sku":"137-4","price":300.0,"currency_code":"USD","in_stock":false}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0719\/1340\/6651\/files\/450236.jpg?v=1784307764","url":"https:\/\/thriftyscooters.com\/products\/naraku-qmb139-52-4mm-performance-cylinder-head-kit-137-4","provider":"Thrifty Scooters","version":"1.0","type":"link"}