{"product_id":"gy6-50cc-139qmb-scooter-52-4mm-big-bore-kit-89cc","title":"GY6 50cc (139QMB) Scooter 52.4mm Big Bore Kit 89cc","description":"\u003ch2\u003e52.4mm Big Bore Kit for GY6 50cc Scooters\u003c\/h2\u003e\u003cp\u003eThis 52.4mm Big Bore Kit is built for GY6 50cc scooters that use the 139QMB engine. With the stock stroke, it raises displacement from 50cc to 89.3cc, and with a 44mm stroker crank it reaches up to 94.9cc. It is one of the \u003ca href=\"\/collections\/gy6-50cc-parts\"\u003eGY6 50cc scooter parts\u003c\/a\u003e available for riders who want more power for off-road use and better efficiency on the trail.\u003c\/p\u003e\u003ch3\u003eBetter Airflow and Power\u003c\/h3\u003e\u003cp\u003eThe kit includes a 52.4mm cylinder and a performance cylinder head with larger valves, 23mm intake and 20mm exhaust, to improve airflow. Port sizes are 20.8mm for the intake and 18.7mm for the exhaust. Together these changes give noticeably quicker throttle response and higher top speed, which suits off-road riders looking for a clear step up in performance.\u003c\/p\u003e\u003ch3\u003eInstallation and Compatibility\u003c\/h3\u003e\u003cp\u003eFitting this kit takes some mechanical skill, since the larger engine needs more fuel and air. For the best results, plan to adjust or replace the carburetor and retune the variator rollers and clutch parts. The kit works with GY6 50cc engines fitted with the 64mm short-valve head, so confirm your engine code before you order.\u003c\/p\u003e\u003ch3\u003eSpecifications\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 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\u003eFits:\u003c\/strong\u003e GY6 50cc 4-stroke 139QMB (QMB139) engines with the 64mm short-valve head\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch3\u003eFitment\u003c\/h3\u003e\u003cp\u003eFits:\u003c\/p\u003e\u003cul\u003e\u003cli\u003eGY6 50cc 4-stroke engine (139QMB, QMB139 engine code, 64mm short-valve head)\u003c\/li\u003e\u003c\/ul\u003e\u003cp\u003e\u003cstrong\u003eHow to choose:\u003c\/strong\u003e Look for the engine code 139QMB or QMB139 stamped on the engine case, and confirm that your original head uses 64mm short-style valves.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eShop more:\u003c\/strong\u003e \u003ca href=\"\/collections\/gy6-50cc-parts\"\u003eGY6 50cc Scooter Parts (139QMB)\u003c\/a\u003e · \u003ca href=\"\/collections\/gy6-scooter-parts\"\u003eGY6 Scooter Parts\u003c\/a\u003e · \u003ca href=\"\/collections\/scooter-cylinder-kits\"\u003eScooter Big Bore \u0026amp; Cylinder Kits\u003c\/a\u003e · \u003ca href=\"\/collections\/scooter-parts\"\u003eScooter Parts\u003c\/a\u003e\u003c\/p\u003e","brand":"Trend Times Toy Stores","offers":[{"title":"Default Title","offer_id":51135780945977,"sku":"TT-16462","price":296.98,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0665\/3358\/9049\/files\/52-4mm-big-bore-kit-89cc-for-gy6-50cc-139qmb-scooters-1.jpg?v=1794349744","url":"https:\/\/www.trendtimes.com\/products\/gy6-50cc-139qmb-scooter-52-4mm-big-bore-kit-89cc","provider":"Trend Times Toy Stores","version":"1.0","type":"link"}