{"product_id":"wpb-welsh-pit-bikes-125-4-speed-gearbox-gn125-bd125-manual-engine","title":"WPB Welsh Pit Bikes 125 4-Speed Gearbox GN125 BD125 Manual Engine","description":"\u003ch2\u003eWPB Welsh Pit Bikes 125 4-Speed Gearbox GN125 BD125\u003c\/h2\u003e\n\u003cp\u003eNew unbranded replacement \u003cstrong\u003e4-speed manual gearbox shaft assembly\u003c\/strong\u003e for selected 125cc pit-bike engines commonly identified as \u003cstrong\u003eGN125 \/ BD125\u003c\/strong\u003e. The assembly is supplied as the two complete transmission shafts with the gears already installed, making it suitable for replacing worn, chipped or damaged internal gearbox components where the dimensions and tooth counts match.\u003c\/p\u003e\n\n\u003ch3\u003eVerified Application\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003e\u003cstrong\u003eWelsh Pit Bikes \/ WPB 125 fitted with the GN125 \/ BD125-type 4-speed manual engine\u003c\/strong\u003e\u003c\/li\u003e\n\u003cli\u003e125cc air-cooled pit-bike engine\u003c\/li\u003e\n\u003cli\u003e4-speed manual clutch transmission\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003cp\u003e\u003cstrong\u003eImportant identification note:\u003c\/strong\u003e “GN125” in this listing refers to the GN125-type \u003cem\u003epit-bike engine designation\u003c\/em\u003e. This gearbox is \u003cstrong\u003enot advertised for the genuine Suzuki GN125 motorcycle\u003c\/strong\u003e, which uses a different 5-speed transmission.\u003c\/p\u003e\n\n\u003ch3\u003eGearbox Specifications\u003c\/h3\u003e\n\u003ch4\u003eOutput Shaft Assembly\u003c\/h4\u003e\n\u003cul\u003e\n\u003cli\u003eOverall shaft length: \u003cstrong\u003e119.5 mm\u003c\/strong\u003e\n\u003c\/li\u003e\n\u003cli\u003eOutput \/ sprocket-side section diameter: \u003cstrong\u003e17 mm\u003c\/strong\u003e\n\u003c\/li\u003e\n\u003cli\u003eBearing-end diameter: \u003cstrong\u003e12 mm\u003c\/strong\u003e\n\u003c\/li\u003e\n\u003cli\u003eGear tooth counts: \u003cstrong\u003e23T \/ 20T \/ 16T \/ 11T\u003c\/strong\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch4\u003eInput Shaft Assembly\u003c\/h4\u003e\n\u003cul\u003e\n\u003cli\u003eOverall shaft length: \u003cstrong\u003e116.5 mm\u003c\/strong\u003e\n\u003c\/li\u003e\n\u003cli\u003eSpline diameter: \u003cstrong\u003e17 mm\u003c\/strong\u003e\n\u003c\/li\u003e\n\u003cli\u003eBearing section diameter: \u003cstrong\u003e12 mm\u003c\/strong\u003e\n\u003c\/li\u003e\n\u003cli\u003eGear tooth counts: \u003cstrong\u003e36T \/ 31T \/ 27T \/ 24T\u003c\/strong\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003eComponents Identified From the Product Photos\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003eComplete input \/ main-shaft gear assembly\u003c\/li\u003e\n\u003cli\u003eComplete output \/ countershaft gear assembly\u003c\/li\u003e\n\u003cli\u003eFour transmission gears on each shaft\u003c\/li\u003e\n\u003cli\u003eSplined shaft ends for transmission \/ drive engagement\u003c\/li\u003e\n\u003cli\u003eMachined bearing journals at the shaft ends\u003c\/li\u003e\n\u003cli\u003eSliding and fixed transmission gears with engagement dogs \/ selector features\u003c\/li\u003e\n\u003cli\u003eFactory-assembled spacers \/ retaining hardware visible on the shafts\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003eOE \u0026amp; Manufacturer Part Number Information\u003c\/h3\u003e\n\u003cp\u003eNo genuine motorcycle OE number or verified manufacturer MPN could be established for this gearbox. Matching aftermarket examples are sold as \u003cstrong\u003eUnbranded\u003c\/strong\u003e with manufacturer part number listed as \u003cstrong\u003eDoes Not Apply\u003c\/strong\u003e. Your Moto Mania UK stock SKU is \u003cstrong\u003e02289-ENG\u003c\/strong\u003e; this is a shop SKU rather than an OE or manufacturer part number.\u003c\/p\u003e\n\n\u003ch3\u003eCompatibility Check — Please Measure Before Ordering\u003c\/h3\u003e\n\u003cp\u003eSeveral visually similar 4-speed 125cc pit-bike gearboxes exist and they are not automatically interchangeable. Before ordering, compare your original gearbox against \u003cstrong\u003eall\u003c\/strong\u003e of the following: shaft lengths, 17 mm splined\/output sections, 12 mm bearing journals, gear tooth counts, selector-dog positions, gear widths and the photographs in this listing.\u003c\/p\u003e\n\u003cp\u003eDo not order by engine capacity, bike colour or model name alone. Engine suppliers changed internal gearbox designs during production, so the physical measurements and tooth counts are the most reliable identification method.\u003c\/p\u003e\n\n\u003ch3\u003eInstallation Notes\u003c\/h3\u003e\n\u003cp\u003eGearbox replacement requires complete engine disassembly and crankcase splitting. Inspect the selector drum, selector forks, bearings, bushes, thrust washers, circlips and crankcases before reassembly. Any worn selector or bearing components should be replaced at the same time. Reassemble using the correct workshop procedure, gasket\/seal components, lubrication and fastener torque settings.\u003c\/p\u003e\n\n\u003ch3\u003eWhat's Included\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003e1 x complete input-shaft gear assembly\u003c\/li\u003e\n\u003cli\u003e1 x complete output-shaft gear assembly\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003eSelector drum, selector forks, bearings, crankcases, gaskets and other engine components are not included unless clearly shown in the photographs.\u003c\/p\u003e\n\n\u003ch3\u003eDelivery \u0026amp; Returns\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003eUK-stock replacement engine component\u003c\/li\u003e\n\u003cli\u003e30-day returns, subject to the item being returned in its original condition\u003c\/li\u003e\n\u003c\/ul\u003e","brand":"Moto Mania UK","offers":[{"title":"Default Title","offer_id":57393246470519,"sku":"02289-ENG","price":36.0,"currency_code":"SHP","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0528\/8771\/6007\/files\/20260806_122457.png?v=1787125681","url":"https:\/\/www.motomaniauk.com\/products\/wpb-welsh-pit-bikes-125-4-speed-gearbox-gn125-bd125-manual-engine","provider":"Moto Mania UK","version":"1.0","type":"link"}